Expect the byte range of the root in the json_view boolean get<T>() test

With JSON_DIAGNOSTIC_POSITIONS, the type_error.302 message starts with
"(bytes 0-4)"; build the expected text with json_view_test::message(),
as the other tests of the root value do.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N5NasAgbDGG28MqXjQvLqp
Signed-off-by: Claude <noreply@anthropic.com>

docs/mkdocs/docs/api/basic_json/get.md

@@ -120,6 +120,16 @@ overload (3).
     See [Number conversion](../../features/types/number_handling.md#number-conversion)
     for more information.
 
+!!! note "Booleans as numbers"
+
+    A JSON boolean converts to `#!cpp 0` or `#!cpp 1` for every arithmetic type **except** [`number_integer_t`](number_integer_t.md),
+    [`number_unsigned_t`](number_unsigned_t.md) and [`number_float_t`](number_float_t.md) (by default `#!cpp std::int64_t`,
+    `#!cpp std::uint64_t`, and `#!cpp double`), for which `#!cpp get<T>()` throws
+    [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) ("type must be number, but is boolean"). So
+    `#!cpp json(true).get<int>()` is `#!cpp 1`, while `#!cpp json(true).get<std::int64_t>()` and
+    `#!cpp json(true).get<double>()` throw. This is the behavior of all 3.x versions;
+    [`basic_json_view::get<T>()`](../basic_json_view/get.md) behaves the same.
+
 !!! note "`std::optional` conversions"
 
     Prior to version 3.13.0, `#!cpp get<std::optional<T>>()` (and other conversions to `std::optional<T>`) failed to

docs/mkdocs/docs/api/basic_json_document/accept.md

@@ -13,9 +13,15 @@ function never throws an exception for invalid input, and the returned `#!cpp bo
 is returned.
 
 The result is the same as that of `BasicJsonType::accept()` by design; the difference is how the check is made. This
-function runs the document's index builder (and discards the index), while `BasicJsonType::accept()` runs the SAX
+function runs the document's builder, which checks the text as [`parse()`](parse.md) does, while
-parser with a handler that ignores every event. Use this one if you go on to parse the same input with
+`BasicJsonType::accept()` runs the SAX parser with a handler that ignores every event. Use this one if you go on to
-[`parse()`](parse.md) anyway, so that both use the same code; either is fine for a plain yes/no answer.
+parse the same input with [`parse()`](parse.md) anyway, so that both use the same code; either is fine for a plain
+yes/no answer.
+
+When both `ignore_comments` and `ignore_trailing_commas` are `#!cpp false` (the default), the builder writes no index.
+With either option set, it builds the index as [`parse()`](parse.md) does and discards it: the result is the same, only
+the time differs. (Neither option needs the index; the variant that skips it exists only for the default options to
+keep the code size down.)
 
 ## Template parameters
 

docs/mkdocs/docs/api/basic_json_view/at.md

@@ -68,9 +68,10 @@ Strong guarantee: there are no changes to the view or the document it refers to.
     - Throws [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) if `ptr` cannot be resolved
       because a reference token is used on a primitive value.
 
-None of these exceptions carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) these exceptions name the JSON
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
+Pointer path of the value within the document, and with
-`JSON_DIAGNOSTICS` enabled.
+[`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) its bytes in the source text (when
+[`materialize()`](materialize.md) sets them).
 
 ## Complexity
 

docs/mkdocs/docs/api/basic_json_view/back.md

@@ -20,9 +20,9 @@ Strong guarantee: there are no changes to the view or the document it refers to.
 Throws [`invalid_iterator.214`](../../home/exceptions.md#jsonexceptioninvalid_iterator214) if the view is
 [null](is_null.md) or [discarded](is_discarded.md), or if it is an empty array or object.
 
-This exception does not carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the exception names the JSON Pointer
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
+path of the value within the document, and with [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md)
-`JSON_DIAGNOSTICS` enabled.
+its bytes in the source text (when [`materialize()`](materialize.md) sets them).
 
 ## Complexity
 

docs/mkdocs/docs/api/basic_json_view/front.md

@@ -20,9 +20,9 @@ Strong guarantee: there are no changes to the view or the document it refers to.
 Throws [`invalid_iterator.214`](../../home/exceptions.md#jsonexceptioninvalid_iterator214) if the view is
 [null](is_null.md) or [discarded](is_discarded.md), or if it is an empty array or object.
 
-This exception does not carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the exception names the JSON Pointer
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
+path of the value within the document, and with [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md)
-`JSON_DIAGNOSTICS` enabled.
+its bytes in the source text (when [`materialize()`](materialize.md) sets them).
 
 ## Complexity
 

docs/mkdocs/docs/api/basic_json_view/get.md

@@ -11,7 +11,8 @@ For the types below, the conversion works directly on the flat index — no `Bas
 
 - `#!cpp bool`
 - arithmetic types other than `#!cpp bool` (for a boolean, `#!cpp 0`/`#!cpp 1`, exactly as for
-  [`BasicJsonType::get<T>()`](../basic_json/get.md))
+  [`BasicJsonType::get<T>()`](../basic_json/get.md#notes), except for `number_integer_t`, `number_unsigned_t` and
+  `number_float_t`, which throw `type_error.302` for a boolean, as `BasicJsonType::get<T>()` does)
 - `#!cpp std::nullptr_t`
 - `#!cpp std::basic_string<char, Traits, Alloc>` (including `string_t`) — a copy of the string
 - [`string_view_t`](index.md#member-types) — **no copy**: the returned view points into the document's
@@ -80,14 +81,13 @@ Strong guarantee: there are no changes to the view or the document it refers to.
 - For every other `T`: whatever [`materialize().get<T>()`](../basic_json/get.md) throws — typically `type_error.302`,
   or whatever a user-provided `from_json()` throws.
 
-None of the exceptions thrown directly by this function or by a `from_json()` that reads the view (the first four
+The exceptions thrown directly by this function or by a `from_json()` that reads the view (the first four bullets
-bullets above) carry a
+above) carry the context of those of `BasicJsonType`: with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the
-[`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no `BasicJsonType` value to point at. An
+JSON Pointer path of the value within the document, and with
-exception thrown while converting through `materialize()` (the last bullet) is different: it is thrown by a real
+[`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) its bytes in the source text. An exception
-`BasicJsonType` value, so it **does** carry a `JSON_DIAGNOSTICS` path if `BasicJsonType` was built with it enabled.
+thrown while converting through `materialize()` (the last bullet) is thrown by the materialized `BasicJsonType` value
-That path is relative to the root of the view's subtree, because `materialize()` builds only the subtree (with parent
+instead: its path is relative to the root of the view's subtree, because `materialize()` builds only the subtree
-pointers): it is empty if the failing value is the subtree's root itself, and it never is the path within the whole
+(with parent pointers), so it is empty if the failing value is the subtree's root itself.
-document.
 
 ## Complexity
 

docs/mkdocs/docs/api/basic_json_view/get_string.md

@@ -22,9 +22,9 @@ Strong guarantee: there are no changes to the view or the document it refers to.
 Throws [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) if the value is not a string; example:
 `"type must be string, but is array"`.
 
-This exception does not carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the exception names the JSON Pointer
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
+path of the value within the document, and with [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md)
-`JSON_DIAGNOSTICS` enabled.
+its bytes in the source text (when [`materialize()`](materialize.md) sets them).
 
 ## Complexity
 

docs/mkdocs/docs/api/basic_json_view/number_token.md

@@ -22,9 +22,9 @@ Strong guarantee: there are no changes to the view or the document it refers to.
 Throws [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) if the value is not a number; example:
 `"type must be number, but is string"`.
 
-This exception does not carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the exception names the JSON Pointer
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
+path of the value within the document, and with [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md)
-`JSON_DIAGNOSTICS` enabled.
+its bytes in the source text (when [`materialize()`](materialize.md) sets them).
 
 ## Complexity
 

docs/mkdocs/docs/api/basic_json_view/operator[].md

@@ -73,9 +73,10 @@ Strong guarantee: there are no changes to the view or the document it refers to.
     - [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) if an array index in `ptr` is not a
       number.
 
-None of these exceptions carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) these exceptions name the JSON
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
+Pointer path of the value within the document, and with
-`JSON_DIAGNOSTICS` enabled.
+[`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) its bytes in the source text (when
+[`materialize()`](materialize.md) sets them).
 
 ## Complexity
 

docs/mkdocs/docs/api/basic_json_view/value.md

@@ -61,9 +61,10 @@ Strong guarantee: there are no changes to the view or the document it refers to.
    `default_value` instead of throwing, exactly as [`BasicJsonType::value`](../basic_json/value.md) catches
    `out_of_range` and returns `default_value`.
 
-None of these exceptions carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) these exceptions name the JSON
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
+Pointer path of the value within the document, and with
-`JSON_DIAGNOSTICS` enabled.
+[`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) its bytes in the source text (when
+[`materialize()`](materialize.md) sets them).
 
 ## Complexity
 

docs/mkdocs/docs/features/json_view.md

@@ -134,9 +134,21 @@ document: `#!cpp auto v = json_document::parse(text).root();` does not compile.
 - **Macros.** [`JSON_STRICT_NUL_HANDLING`](../api/macros/json_strict_nul_handling.md) and
   [`JSON_NOEXCEPTION`](../api/macros/json_noexception.md)/[`JSON_THROW_USER`](../api/macros/json_throw_user.md)
   behave the same way they do for `<nlohmann/json.hpp>`. These are the macros that change what the parser accepts or
-  how it reports errors. The others either do not apply ([`JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md)
+  how it reports errors. Two more macros add context to the exceptions of views, as they do for those of
-  needs parent pointers in `basic_json` values) or only affect the values `materialize()` produces, through
+  `#!cpp basic_json`:
-  `BasicJsonType`.
+
+    - With [`JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md), an exception names the JSON Pointer path of the
+      value within the document.
+    - With [`JSON_DIAGNOSTIC_POSITIONS`](../api/macros/json_diagnostic_positions.md), an exception names the bytes of
+      the value in the source text.
+
+    A view has neither parent pointers nor stored positions, so both are found from the document's index when the
+    exception is thrown. This takes time linear in the size of the document. One exception has neither:
+    `key()` of an iterator over an array or a primitive value
+    ([`invalid_iterator.207`](../home/exceptions.md#jsonexceptioninvalid_iterator207)), because a view's iterator does
+    not know the value it iterates over.
+
+    The other macros only affect the values `materialize()` produces, through `BasicJsonType`.
 
 ## What is different
 
@@ -167,10 +179,6 @@ document: `#!cpp auto v = json_document::parse(text).root();` does not compile.
   [`at`](../api/basic_json_view/at.md) throws for every missing value.
 - **Duplicate keys: lookups find the first member, `parse()` keeps the last.** See [Duplicate keys](#duplicate-keys)
   below.
-- **No [`JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md) path.** Exceptions thrown by `basic_json_view`'s own
-  element access and lookup functions never carry the JSON Pointer path `JSON_DIAGNOSTICS` would otherwise add: the
-  view has no `basic_json` value to point at, so the exception is created without one, regardless of how
-  `BasicJsonType` was built.
 - **Ordering comparisons are not provided** by `basic_json_view` — there is no `#!cpp operator<`.
   [`operator==`](../api/basic_json_view/operator_eq.md) and [`operator!=`](../api/basic_json_view/operator_ne.md) are
   provided, though: two views, or a view and a `BasicJsonType` value, compare equal exactly when
@@ -253,6 +261,34 @@ Two conversions never copy at all:
 
 Both results are only valid as long as the view — and, for a string with no escapes, the borrowed source text — is.
 
+### `string_view` members
+
+A struct whose member is a `#!cpp std::string_view` (C++17) can be decoded from a view with the
+`NLOHMANN_DEFINE_TYPE_*` macros, and the member is not copied either: for a string without escape sequences it points
+into the document's source text, and for a string with escape sequences into the document's buffer of decoded strings.
+The member is valid as long as the document is alive and, for a document that
+[borrows its source text](#ownership-and-lifetime) (as [`parse()`](../api/basic_json_document/parse.md) does for
+an lvalue `#!cpp std::string`, a `#!cpp std::string_view`, or a C string), as long as that text is.
+
+```cpp
+struct record
+{
+    std::string_view name;
+    int count;
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(record, name, count)
+};
+
+const std::string text = R"({"name": "widget", "count": 3})";
+const json_document doc = json_document::parse(text);  // borrows text
+const record r = doc.root().get<record>();             // r.name points into text, valid while text and doc are
+```
+
+!!! warning "Decoding into a `string_view` from a `json` value dangles at once"
+
+    The same struct also compiles with `#!cpp json::parse(text).get<record>()`, but there `name` points into the
+    temporary `json` value, which is destroyed at the end of the statement. Use a named
+    [`json_document`](../api/json_document.md), as above, to decode such a struct.
+
 ## Writing generic code
 
 A view's type names its `BasicJsonType` and its [`view_mode`](../api/view_mode.md):
@@ -329,14 +365,10 @@ Its body may only use what views and `basic_json` have in common: the type check
 a view does not have; such a type is converted through `materialize()`. A `from_json()` for `json` only is
 converted through `materialize()` as well.
 
-Two things differ when a `from_json()` reads the view:
+One thing differs when a `from_json()` reads the view: members looked up by name (`at()`, `value()`, ... and thus
-
+the macros) find the **first** member with a repeated key, see [Duplicate keys](#duplicate-keys);
-- **Duplicate keys.** Members looked up by name (`at()`, `value()`, ... and thus the macros) find the **first** member
+`#!cpp materialize().get<T>()` would see the last one. Containers built from an object, such as `#!cpp std::map`,
-  with a repeated key, see [Duplicate keys](#duplicate-keys); `#!cpp materialize().get<T>()` would see the last one.
+keep the **last** value either way, as [`parse()`](../api/basic_json/parse.md) does.
-  Containers built from an object, such as `#!cpp std::map`, keep the **last** value either way, as
-  [`parse()`](../api/basic_json/parse.md) does.
-- **[`JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md).** Exceptions thrown by the view carry no path to the
-  value.
 
 `to_json()` is unaffected: it writes `basic_json` values, never views.
 

docs/mkdocs/docs/home/debugging.md

@@ -10,6 +10,13 @@ at its root, a [Natvis](https://learn.microsoft.com/en-us/visualstudio/debugger/
 file that gives `json`/`ordered_json` values a friendly, key/value debugger view instead of showing raw internal
 fields, when debugging with the MSVC debug engine (`cppvsdbg`) in Visual Studio or VS Code.
 
+The file also has visualizers for `json_document` and `json_view` (and their `ordered_json`/editable variants). They
+show the value of the document or view, and its elements as an expandable list. Because a document is only a flat index
+into the source text, the strings of the direct elements are shown, but the elements of nested arrays and objects are
+shown as index nodes (their kind, size, and numbers; strings only by length). Arrays and objects that have been edited
+in a `json_editable_document` are not expanded. The visualizers read the internal layout of the MSVC STL (`std::array`,
+`std::unique_ptr`).
+
 The checked-in visualizers cover namespace variants with zero, one, or two ABI tags. Configurations with three or more
 ABI tags are not covered and may show raw internal fields instead. To generate a Natvis file for such a configuration:
 
@@ -29,7 +36,7 @@ ABI tags are not covered and may show raw internal fields instead. To generate a
 
 4. Use the generated file instead of `nlohmann_json.natvis`.
 
-`--abi-tags` can be repeated for several configurations, and `--all` generates every combination (about 60 MB for 12
+`--abi-tags` can be repeated for several configurations, and `--all` generates every combination (about 60 MB for 11
 ABI tags, doubling with each further tag). See
 [`tools/generate_natvis`](https://github.com/nlohmann/json/tree/develop/tools/generate_natvis) for all options.
 

include/nlohmann/detail/exceptions.hpp

@@ -431,6 +431,28 @@ std::nullptr_t exception_context(const View& /*unused*/) noexcept
     return nullptr;
 }
 
+namespace view
+{
+// the path and bytes of the value of a view (defined in <nlohmann/detail/view/errors.hpp>)
+template<typename View>
+std::string diagnostics_of(const View& v);
+}  // namespace view
+
+// what goes in front of the message of an exception about j: nothing for a
+// basic_json value (exception_context() passes the value itself), the context
+// basic_json would add (JSON_DIAGNOSTICS, JSON_DIAGNOSTIC_POSITIONS) for a view
+template<typename BasicJsonType, enable_if_t<is_basic_json<BasicJsonType>::value, int> = 0>
+const char* exception_prefix(const BasicJsonType& /*unused*/) noexcept
+{
+    return "";
+}
+
+template<typename View, enable_if_t<is_json_view<View>::value, int> = 0>
+std::string exception_prefix(const View& v)
+{
+    return view::diagnostics_of(v);
+}
+
 /*!
 @brief throws because @a j does not have the type a conversion expects
 @param[in] expected  the expected type(s), e.g. "array" or "binary or array"
@@ -442,7 +464,7 @@ JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_type_must_be(const cha
 {
     static_cast<void>(expected); // unused when JSON_NOEXCEPTION is defined
     static_cast<void>(j);
-    JSON_THROW(type_error::create(exception_id::type_mismatch, concat("type must be ", expected, ", but is ", j.type_name()), exception_context(j)));
+    JSON_THROW(type_error::create(exception_id::type_mismatch, concat(exception_prefix(j), "type must be ", expected, ", but is ", j.type_name()), exception_context(j)));
 }
 
 /*!

include/nlohmann/detail/input/binary_reader.hpp

@@ -22,6 +22,7 @@
     #include <bit>  //byteswap
 #endif
 
+#include <nlohmann/detail/bit_ops.hpp>
 #include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/input/input_adapters.hpp>
 #include <nlohmann/detail/input/json_sax.hpp>
@@ -465,15 +466,17 @@ class binary_reader
             }
 
             const std::size_t element_type_parse_position = chars_read;
+            // an array's elements are named "0", "1", ... in the wire format,
+            // and those names are not passed on: they are skipped unless
+            // error_handler_t::strict must reject ill-formed UTF-8 in them
+            const bool is_object = container_stack.back().is_object;
             key.clear();
-            if (JSON_HEDLEY_UNLIKELY(!get_bson_cstr(key)))
+            if (JSON_HEDLEY_UNLIKELY(!get_bson_cstr(key, is_object || error_handler == error_handler_t::strict)))
             {
                 return false;
             }
 
-            // an array's elements are named "0", "1", ... in the wire format,
+            if (is_object && !sax->key(key))
-            // and those names are not passed on
-            if (container_stack.back().is_object && !sax->key(key))
             {
                 return false;
             }
@@ -489,14 +492,18 @@ class binary_reader
     @brief Parses a C-style string from the BSON input.
     @param[in,out] result  A reference to the string variable where the read
                             string is to be stored.
+    @param[in] store  whether the characters are needed; if not (the names of
+                      an array's elements), they are skipped and @a result may
+                      be left unchanged, and they are not checked against
+                      @ref error_handler
     @return `true` if the \\x00-byte indicating the end of the string was
              encountered before the EOF; false` indicates an unexpected EOF.
     */
-    bool get_bson_cstr(string_t& result)
+    bool get_bson_cstr(string_t& result, const bool store = true)
     {
-        if (get_bson_cstr_bulk(result, std::integral_constant<bool, bulk_scan> {}))
+        if (get_bson_cstr_bulk(result, store, std::integral_constant<bool, bulk_scan> {}))
         {
-            return check_string_utf8(result, "key");
+            return !store || check_string_utf8(result, "key");
         }
 
         auto out = std::back_inserter(result);
@@ -509,7 +516,7 @@ class binary_reader
             }
             if (current == 0x00)
             {
-                return check_string_utf8(result, "key");
+                return !store || check_string_utf8(result, "key");
             }
             *out++ = static_cast<typename string_t::value_type>(current);
         }
@@ -519,10 +526,11 @@ class binary_reader
     @brief read a C-style string from contiguous input in one step
 
     @param[in,out] result  the string to append to
+    @param[in] store  whether to append the characters to @a result
     @return whether the string was read; if the input has no \\x00-byte, nothing
             is read, and @ref get_bson_cstr reports the end of the input
     */
-    bool get_bson_cstr_bulk(string_t& result, std::true_type /*bulk*/)
+    bool get_bson_cstr_bulk(string_t& result, const bool store, std::true_type /*bulk*/)
     {
         const std::size_t remaining = ia.bulk_remaining();
         if (remaining == 0)
@@ -530,18 +538,15 @@ class binary_reader
             return false;
         }
         const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
-        // a plain loop rather than std::memchr: most keys are short (array
+        const std::size_t length = find_zero_byte(data, remaining);
-        // indices are keys, too), and the call would cost more than it saves
-        std::size_t length = 0;
-        while (length < remaining && data[length] != 0x00)
-        {
-            ++length;
-        }
         if (length == remaining)
         {
             return false;
         }
-        result.append(reinterpret_cast<const typename string_t::value_type*>(data), length);
+        if (store)
+        {
+            result.append(reinterpret_cast<const typename string_t::value_type*>(data), length);
+        }
         // consume the string and its \x00-byte, as the byte-wise path does
         ia.bulk_skip(length + 1);
         chars_read += length + 1;
@@ -550,7 +555,7 @@ class binary_reader
     }
 
     /// input that is not contiguous: C-style strings are read byte by byte
-    bool get_bson_cstr_bulk(string_t& /*result*/, std::false_type /*bulk*/) const noexcept
+    bool get_bson_cstr_bulk(string_t& /*result*/, const bool /*store*/, std::false_type /*bulk*/) const noexcept
     {
         return false;
     }
@@ -741,11 +746,13 @@ class binary_reader
     bool get_cbor_negative_integer()
     {
         NumberType number{};
-        if (JSON_HEDLEY_UNLIKELY(!get_number(number)))
+        return get_number(number) && emit_cbor_negative_integer(number);
-        {
+    }
-            return false;
-        }
 
+    /// pass the CBOR negative integer -1 - @a number to the SAX parser
+    template<typename NumberType>
+    bool emit_cbor_negative_integer(const NumberType number)
+    {
         // the value is -1 - number, which fits into number_integer_t
         // whenever number does; the outer cast undoes the integral promotion
         // for number_integer_t types narrower than int
@@ -970,7 +977,7 @@ class binary_reader
             case 0x95:
             case 0x96:
             case 0x97:
-                return enter_array(conditional_static_cast<std::size_t>(static_cast<unsigned int>(current) & 0x1Fu));
+                return enter_cbor_array(conditional_static_cast<std::size_t>(static_cast<unsigned int>(current) & 0x1Fu));
 
             case 0x98: // array (one-byte uint8_t for n follows)
             case 0x99: // array (two-byte uint16_t for n follow)
@@ -979,7 +986,7 @@ class binary_reader
             {
                 std::uint64_t len{};
                 std::size_t size{};
-                return get_cbor_argument(len) && get_cbor_container_size(len, size, "array") && enter_array(size);
+                return get_cbor_argument(len) && get_cbor_container_size(len, size, "array") && enter_cbor_array(size);
             }
 
             case 0x9F: // array (indefinite length)
@@ -1133,16 +1140,10 @@ class binary_reader
                 return get_half_float(false);
 
             case 0xFA: // Single-Precision Float (four-byte IEEE 754)
-            {
+                return get_cbor_float<float>();
-                float number{};
-                return get_number(number) && emit_float(number);
-            }
 
             case 0xFB: // Double-Precision Float (eight-byte IEEE 754)
-            {
+                return get_cbor_float<double>();
-                double number{};
-                return get_number(number) && emit_float(number);
-            }
 
             default: // anything else (0xFF is handled inside the other types)
             {
@@ -1151,6 +1152,14 @@ class binary_reader
         }
     }
 
+    /// read a single- or double-precision float
+    template<typename NumberType>
+    bool get_cbor_float()
+    {
+        NumberType number{};
+        return get_number(number) && emit_float(number);
+    }
+
     /*!
     @brief reports a nested indefinite-length CBOR string or byte array
     @param[in] type_name  name of the rejected string type
@@ -1676,6 +1685,155 @@ class binary_reader
         return true;
     }
 
+    /*!
+    @brief read a big-endian number of type @a NumberType at @a data
+    */
+    template<typename NumberType>
+    NumberType load_big_endian(const unsigned char* data) const noexcept
+    {
+        NumberType result{};
+        std::memcpy(&result, data, sizeof(NumberType));
+        if (is_little_endian)
+        {
+            byte_swap(result);
+        }
+        return result;
+    }
+
+    /*!
+    @brief read the integers, floats, booleans, and nulls that follow in a
+           definite-length array, without the per-element bookkeeping of
+           @ref parse_cbor_internal
+
+    Stops at the end of the array, at any other kind of value, and when fewer
+    than 9 bytes (the longest of these values) are left in the input, leaving
+    those to @ref parse_cbor_value, which reads them the same way.
+
+    Out of line, so that @ref parse_cbor_value stays small enough to be inlined.
+
+    The array is the one on top of @ref container_stack; its count of
+    elements not yet read is updated.
+
+    @return whether the SAX parser accepted the values
+    */
+    JSON_HEDLEY_NEVER_INLINE
+    bool parse_cbor_scalar_run(std::true_type /*bulk*/)
+    {
+        // nothing pushes onto the stack while the run reads scalars
+        std::size_t& remaining = container_stack.back().remaining;
+        while (remaining != 0 && ia.bulk_remaining() >= 9)
+        {
+            const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
+            const unsigned char head = data[0];
+            std::size_t size = 0;
+            bool accepted = false;
+            switch (head)
+            {
+                case 0x18:
+                    size = 2;
+                    accepted = emit_unsigned(data[1]);
+                    break;
+                case 0x19:
+                    size = 3;
+                    accepted = emit_unsigned(load_big_endian<std::uint16_t>(data + 1));
+                    break;
+                case 0x1A:
+                    size = 5;
+                    accepted = emit_unsigned(load_big_endian<std::uint32_t>(data + 1));
+                    break;
+                case 0x1B:
+                    size = 9;
+                    accepted = emit_unsigned(load_big_endian<std::uint64_t>(data + 1));
+                    break;
+                case 0x38:
+                    size = 2;
+                    accepted = emit_cbor_negative_integer(data[1]);
+                    break;
+                case 0x39:
+                    size = 3;
+                    accepted = emit_cbor_negative_integer(load_big_endian<std::uint16_t>(data + 1));
+                    break;
+                case 0x3A:
+                    size = 5;
+                    accepted = emit_cbor_negative_integer(load_big_endian<std::uint32_t>(data + 1));
+                    break;
+                case 0x3B:
+                    size = 9;
+                    accepted = emit_cbor_negative_integer(load_big_endian<std::uint64_t>(data + 1));
+                    break;
+                case 0xF4:
+                    size = 1;
+                    accepted = sax->boolean(false);
+                    break;
+                case 0xF5:
+                    size = 1;
+                    accepted = sax->boolean(true);
+                    break;
+                case 0xF6:
+                    size = 1;
+                    accepted = sax->null();
+                    break;
+                case 0xFA:
+                    size = 5;
+                    accepted = emit_float(load_big_endian<float>(data + 1));
+                    break;
+                case 0xFB:
+                    size = 9;
+                    accepted = emit_float(load_big_endian<double>(data + 1));
+                    break;
+                default:
+                    if (head <= 0x17)
+                    {
+                        size = 1;
+                        accepted = sax->number_unsigned(static_cast<number_unsigned_t>(head));
+                    }
+                    else if (head >= 0x20 && head <= 0x37)
+                    {
+                        size = 1;
+                        accepted = sax->number_integer(static_cast<std::int8_t>(0x20 - 1 - head));
+                    }
+                    else
+                    {
+                        // any other value is read by parse_cbor_value
+                        return true;
+                    }
+                    break;
+            }
+            // as if read by get() and get_number(): current is the head byte
+            ia.bulk_skip(size);
+            chars_read += size;
+            current = head;
+            --remaining;
+            if (JSON_HEDLEY_UNLIKELY(!accepted))
+            {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /*!
+    @brief open a definite-length array and read the scalars it begins with
+           (see @ref parse_cbor_scalar_run)
+
+    Only the start of an array is tried, which covers arrays of numbers
+    (e.g. coordinates) but costs arrays of other values only one call, not one
+    per element.
+
+    @param[in] len  the number of elements
+    @return whether the SAX parser accepted the array and the values read
+    */
+    bool enter_cbor_array(const std::size_t len)
+    {
+        return enter_array(len) && (len == 0 || parse_cbor_scalar_run(std::integral_constant<bool, bulk_scan> {}));
+    }
+
+    /// input that is not contiguous: every value is read by parse_cbor_value
+    bool parse_cbor_scalar_run(std::false_type /*bulk*/) const noexcept
+    {
+        return true;
+    }
+
     /*!
     @brief read a CBOR value and everything nested inside it
 
@@ -1705,6 +1863,7 @@ class binary_reader
                 // pop_back() below, which destroys the container_stack element
                 // it would otherwise alias
                 const container_frame top = container_stack.back();
+                const bool is_object = top.is_object;
                 bool at_end = false;
 
                 if (top.remaining != npos)
@@ -1716,7 +1875,7 @@ class binary_reader
                     {
                         // claim the element about to be read
                         --container_stack.back().remaining;
-                        if (top.is_object)
+                        if (is_object)
                         {
                             get();
                         }
@@ -1729,7 +1888,7 @@ class binary_reader
                     // Testing for it consumes a byte, which is the first byte
                     // of the next element when it is not one.
                     at_end = (get() == 0xFF);
-                    fetch = top.is_object;
+                    fetch = is_object;
                 }
 
                 if (at_end)
@@ -1746,7 +1905,7 @@ class binary_reader
                     continue;
                 }
 
-                if (top.is_object)
+                if (is_object)
                 {
                     if (JSON_HEDLEY_UNLIKELY(!skip_cbor_key_tags(tag_handler)))
                     {
@@ -1971,7 +2130,7 @@ class binary_reader
             case 0x9D:
             case 0x9E:
             case 0x9F:
-                return enter_array(conditional_static_cast<std::size_t>(static_cast<unsigned int>(current) & 0x0Fu));
+                return enter_msgpack_array(conditional_static_cast<std::size_t>(static_cast<unsigned int>(current) & 0x0Fu));
 
             // fixstr
             case 0xA0:
@@ -2102,13 +2261,13 @@ class binary_reader
             case 0xDC: // array 16
             {
                 std::uint16_t len{};
-                return get_number(len) && enter_array(static_cast<std::size_t>(len));
+                return get_number(len) && enter_msgpack_array(static_cast<std::size_t>(len));
             }
 
             case 0xDD: // array 32
             {
                 std::uint32_t len{};
-                return get_number(len) && enter_array(conditional_static_cast<std::size_t>(len));
+                return get_number(len) && enter_msgpack_array(conditional_static_cast<std::size_t>(len));
             }
 
             case 0xDE: // map 16
@@ -2450,6 +2609,137 @@ class binary_reader
         }
     }
 
+    /*!
+    @brief read the integers, floats, booleans, and nils that follow in a
+           MessagePack array, without the per-element bookkeeping of
+           @ref parse_msgpack_internal
+
+    Stops at the end of the array, at any other kind of value, and when fewer
+    than 9 bytes (the longest of these values) are left in the input, leaving
+    those to @ref parse_msgpack_value, which reads them the same way.
+
+    Out of line, so that @ref parse_msgpack_value stays small enough to be inlined.
+
+    The array is the one on top of @ref container_stack; its count of
+    elements not yet read is updated.
+
+    @return whether the SAX parser accepted the values
+    */
+    JSON_HEDLEY_NEVER_INLINE
+    bool parse_msgpack_scalar_run(std::true_type /*bulk*/)
+    {
+        // nothing pushes onto the stack while the run reads scalars
+        std::size_t& remaining = container_stack.back().remaining;
+        while (remaining != 0 && ia.bulk_remaining() >= 9)
+        {
+            const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
+            const unsigned char head = data[0];
+            std::size_t size = 0;
+            bool accepted = false;
+            switch (head)
+            {
+                case 0xC0: // nil
+                    size = 1;
+                    accepted = sax->null();
+                    break;
+                case 0xC2: // false
+                    size = 1;
+                    accepted = sax->boolean(false);
+                    break;
+                case 0xC3: // true
+                    size = 1;
+                    accepted = sax->boolean(true);
+                    break;
+                case 0xCA: // float 32
+                    size = 5;
+                    accepted = emit_float(load_big_endian<float>(data + 1));
+                    break;
+                case 0xCB: // float 64
+                    size = 9;
+                    accepted = emit_float(load_big_endian<double>(data + 1));
+                    break;
+                case 0xCC: // uint 8
+                    size = 2;
+                    accepted = emit_unsigned(data[1]);
+                    break;
+                case 0xCD: // uint 16
+                    size = 3;
+                    accepted = emit_unsigned(load_big_endian<std::uint16_t>(data + 1));
+                    break;
+                case 0xCE: // uint 32
+                    size = 5;
+                    accepted = emit_unsigned(load_big_endian<std::uint32_t>(data + 1));
+                    break;
+                case 0xCF: // uint 64
+                    size = 9;
+                    accepted = emit_unsigned(load_big_endian<std::uint64_t>(data + 1));
+                    break;
+                case 0xD0: // int 8
+                    size = 2;
+                    accepted = emit_signed(static_cast<std::int8_t>(data[1]));
+                    break;
+                case 0xD1: // int 16
+                    size = 3;
+                    accepted = emit_signed(load_big_endian<std::int16_t>(data + 1));
+                    break;
+                case 0xD2: // int 32
+                    size = 5;
+                    accepted = emit_signed(load_big_endian<std::int32_t>(data + 1));
+                    break;
+                case 0xD3: // int 64
+                    size = 9;
+                    accepted = emit_signed(load_big_endian<std::int64_t>(data + 1));
+                    break;
+                default:
+                    if (head <= 0x7F)
+                    {
+                        // positive fixint
+                        size = 1;
+                        accepted = sax->number_unsigned(static_cast<number_unsigned_t>(head));
+                    }
+                    else if (head >= 0xE0)
+                    {
+                        // negative fixint
+                        size = 1;
+                        accepted = sax->number_integer(static_cast<std::int8_t>(head));
+                    }
+                    else
+                    {
+                        // any other value is read by parse_msgpack_value
+                        return true;
+                    }
+                    break;
+            }
+            // as if read by get() and get_number(): current is the last byte
+            ia.bulk_skip(size);
+            chars_read += size;
+            current = data[size - 1];
+            --remaining;
+            if (JSON_HEDLEY_UNLIKELY(!accepted))
+            {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /*!
+    @brief open a MessagePack array and read the scalars it begins with (see
+           @ref parse_msgpack_scalar_run)
+    @param[in] len  the number of elements
+    @return whether the SAX parser accepted the array and the values read
+    */
+    bool enter_msgpack_array(const std::size_t len)
+    {
+        return enter_array(len) && (len == 0 || parse_msgpack_scalar_run(std::integral_constant<bool, bulk_scan> {}));
+    }
+
+    /// input that is not contiguous: every value is read by parse_msgpack_value
+    bool parse_msgpack_scalar_run(std::false_type /*bulk*/) const noexcept
+    {
+        return true;
+    }
+
     /*!
     @brief read a MessagePack value and everything nested inside it
 
@@ -3255,6 +3545,107 @@ class binary_reader
         return unexpected_byte("invalid byte", "value");
     }
 
+    /*!
+    @brief read the elements of an optimized array of numbers (type marker
+           @a type) that are in the input, in one loop, without the
+           per-element bookkeeping of @ref parse_ubjson_internal
+
+    Values are emitted as @ref get_ubjson_value emits them. Types other than
+    the fixed-size integers and floats are left to @ref get_ubjson_value, as
+    are the elements the input ends before.
+
+    @param[in,out] remaining  the number of elements not yet read
+    @param[in] type  the type marker of the elements
+    @return whether the SAX parser accepted the values
+    */
+    JSON_HEDLEY_NEVER_INLINE
+    bool parse_ubjson_typed_run(std::size_t& remaining, const char_int_type type, std::true_type /*bulk*/)
+    {
+        const bool bjdata = input_format == input_format_t::bjdata;
+        switch (type)
+        {
+            case 'U':
+                return parse_ubjson_typed_run<std::uint8_t>(remaining);
+            case 'i':
+                return parse_ubjson_typed_run<std::int8_t>(remaining);
+            case 'I':
+                return parse_ubjson_typed_run<std::int16_t>(remaining);
+            case 'l':
+                return parse_ubjson_typed_run<std::int32_t>(remaining);
+            case 'L':
+                return parse_ubjson_typed_run<std::int64_t>(remaining);
+            case 'u':
+                return !bjdata || parse_ubjson_typed_run<std::uint16_t>(remaining);
+            case 'm':
+                return !bjdata || parse_ubjson_typed_run<std::uint32_t>(remaining);
+            case 'M':
+                return !bjdata || parse_ubjson_typed_run<std::uint64_t>(remaining);
+            case 'd':
+                return parse_ubjson_typed_run<float>(remaining);
+            case 'D':
+                return parse_ubjson_typed_run<double>(remaining);
+            default:
+                return true;
+        }
+    }
+
+    /// input that is not contiguous: every element is read by get_ubjson_value
+    bool parse_ubjson_typed_run(std::size_t& /*remaining*/, const char_int_type /*type*/, std::false_type /*bulk*/) const noexcept
+    {
+        return true;
+    }
+
+    template<typename NumberType>
+    bool parse_ubjson_typed_run(std::size_t& remaining)
+    {
+        constexpr std::size_t size = sizeof(NumberType);
+        const std::size_t count = (std::min)(remaining, ia.bulk_remaining() / size);
+        if (count == 0)
+        {
+            return true;
+        }
+        const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
+        // UBJSON stores numbers big-endian, BJData little-endian
+        const bool swap = is_little_endian != (input_format == input_format_t::bjdata);
+        std::size_t read = 0;
+        bool accepted = true;
+        while (read < count && accepted)
+        {
+            NumberType number{};
+            std::memcpy(&number, data + (read * size), size);
+            if (swap)
+            {
+                byte_swap(number);
+            }
+            ++read;
+            accepted = emit_ubjson_number(number);
+        }
+        // as if read by get_number(): current is the last byte read
+        ia.bulk_skip(read * size);
+        chars_read += read * size;
+        current = data[(read * size) - 1];
+        remaining -= read;
+        return accepted;
+    }
+
+    template<typename NumberType, enable_if_t<std::is_floating_point<NumberType>::value, int> = 0>
+    bool emit_ubjson_number(const NumberType number)
+    {
+        return emit_float(number);
+    }
+
+    template < typename NumberType, enable_if_t < std::is_integral<NumberType>::value&& std::is_signed<NumberType>::value, int > = 0 >
+    bool emit_ubjson_number(const NumberType number)
+    {
+        return emit_signed(number);
+    }
+
+    template < typename NumberType, enable_if_t < std::is_integral<NumberType>::value&& !std::is_signed<NumberType>::value, int > = 0 >
+    bool emit_ubjson_number(const NumberType number)
+    {
+        return emit_unsigned(number);
+    }
+
     /*!
     @return whether array creation completed
     */
@@ -3290,7 +3681,15 @@ class binary_reader
                 return false;
             }
 
-            for (std::size_t i = 0; i < size_and_type.first; ++i)
+            // the numbers that are in the input, in one loop; the rest (if
+            // the input ends early) one by one below
+            std::size_t remaining = size_and_type.first;
+            if (!nd_is_char && JSON_HEDLEY_UNLIKELY(!parse_ubjson_typed_run(remaining, size_and_type.second, std::integral_constant<bool, bulk_scan> {})))
+            {
+                return false;
+            }
+
+            for (std::size_t i = size_and_type.first - remaining; i < size_and_type.first; ++i)
             {
                 if (nd_is_char)
                 {
@@ -3350,7 +3749,8 @@ class binary_reader
                 container_stack.back().remaining = 0;
             }
 
-            return true;
+            return size_and_type.second == 0
+                   || parse_ubjson_typed_run(container_stack.back().remaining, size_and_type.second, std::integral_constant<bool, bulk_scan> {});
         }
 
         return enter_array(detail::unknown_size());
@@ -3691,13 +4091,13 @@ class binary_reader
                 return sax->null();
 
             case 0xFB:
-                return sax->number_float(static_cast<number_float_t>(-1.0), "");
+                return sax->number_float(static_cast<number_float_t>(-1.0), no_source);
 
             case 0xFC:
-                return sax->number_float(static_cast<number_float_t>(0.0), "");
+                return sax->number_float(static_cast<number_float_t>(0.0), no_source);
 
             case 0xFD:
-                return sax->number_float(static_cast<number_float_t>(1.0), "");
+                return sax->number_float(static_cast<number_float_t>(1.0), no_source);
 
             case 0xFF: // empty string
             {
@@ -4020,7 +4420,12 @@ class binary_reader
     `char_traits<char_type>::eof()` in that case.
 
     @return character read from the input
+
+    @note always inlined: GCC otherwise stops inlining the stream adapter's
+          get_character() into parse_cbor_internal once that function grows
+          (+0.45 % instructions for CBOR from a std::istringstream with GCC 13)
     */
+    JSON_HEDLEY_ALWAYS_INLINE
     char_int_type get()
     {
         ++chars_read;
@@ -4066,6 +4471,27 @@ class binary_reader
         return current;
     }
 
+    /// reverse the byte order of a double with a single byteswap(): GCC does
+    /// not merge the byte-wise swap of the generic version into one
+    static void byte_swap(double& number) noexcept
+    {
+        static_assert(sizeof(double) == sizeof(std::uint64_t), "double must have 64 bits");
+        std::uint64_t bits{};
+        std::memcpy(&bits, &number, sizeof(bits));
+        bits = byteswap(bits);
+        std::memcpy(&number, &bits, sizeof(bits));
+    }
+
+    /// reverse the byte order of a float with a single byteswap()
+    static void byte_swap(float& number) noexcept
+    {
+        static_assert(sizeof(float) == sizeof(std::uint32_t), "float must have 32 bits");
+        std::uint32_t bits{};
+        std::memcpy(&bits, &number, sizeof(bits));
+        bits = byteswap(bits);
+        std::memcpy(&number, &bits, sizeof(bits));
+    }
+
     template<class NumberType>
     static void byte_swap(NumberType& number)
     {
@@ -4201,7 +4627,7 @@ class binary_reader
         {
             return out_of_range_error(exception_id::number_overflow, "number overflow", "value");
         }
-        return sax->number_float(result, "");
+        return sax->number_float(result, no_source);
     }
 
     /*!
@@ -4261,7 +4687,7 @@ class binary_reader
         }();
         return sax->number_float((half & 0x8000u) != 0
                                  ? static_cast<number_float_t>(-val)
-                                 : static_cast<number_float_t>(val), "");
+                                 : static_cast<number_float_t>(val), no_source);
     }
 
     /*!
@@ -4293,6 +4719,19 @@ class binary_reader
         return get_bytes(len, "string", result);
     }
 
+    /// whether @a s is valid UTF-8: ASCII eight bytes at a time, the rest
+    /// sequence by sequence (as the binary writers check strings)
+    static bool is_valid_utf8_string(const string_t& s, std::true_type /*is_byte*/) noexcept
+    {
+        return valid_utf8_string(reinterpret_cast<const unsigned char*>(s.data()), s.size());
+    }
+
+    /// whether @a s, of a character type wider than a byte, is valid UTF-8
+    static bool is_valid_utf8_string(const string_t& s, std::false_type /*is_byte*/) noexcept
+    {
+        return is_valid_utf8(s);
+    }
+
     /*!
     @brief validate a decoded text string (value or object key) against @ref error_handler
 
@@ -4312,7 +4751,16 @@ class binary_reader
     */
     bool check_string_utf8(string_t& result, const char* context)
     {
-        if (error_handler == error_handler_t::keep || is_valid_utf8(result))
+        return error_handler == error_handler_t::keep || check_string_utf8_handler(result, context);
+    }
+
+    /// @ref check_string_utf8 for an error handler other than @ref
+    /// error_handler_t::keep; out of line, so that reading strings without a
+    /// check does not pay for the code of the check
+    JSON_HEDLEY_NEVER_INLINE
+    bool check_string_utf8_handler(string_t& result, const char* context)
+    {
+        if (is_valid_utf8_string(result, std::integral_constant<bool, sizeof(typename string_t::value_type) == 1>()))
         {
             return true;
         }
@@ -4586,6 +5034,10 @@ class binary_reader
     /// the SAX parser
     json_sax_t* sax = nullptr;
 
+    /// the (empty) source text of every number_float event: binary formats
+    /// have none, and a string_t built for each float would cost more
+    const string_t no_source{};
+
     /// the containers that have been opened and not closed yet; see @ref container_frame
     std::vector<container_frame> container_stack{};
 

include/nlohmann/detail/input/lexer.hpp

@@ -209,8 +209,13 @@ constexpr bool input_adapter_bulk_window(std::false_type /*detected*/)
 @brief lexical analysis
 
 This class organizes the lexical analysis during JSON deserialization.
+
+DiscardValues: the caller only needs the token types and never looks at the values of number and string tokens (only
+accept(), which parses through json_sax_acceptor). A template parameter rather than a member, so that the lexer of
+parse() is compiled without the paths of accept(): with both string scans in one scan(), parse() was up to 2 % slower
+on Apple M1.
 */
-template<typename BasicJsonType, typename InputAdapterType>
+template<typename BasicJsonType, typename InputAdapterType, bool DiscardValues = false>
 class lexer : public lexer_base<BasicJsonType>
 {
     using number_integer_t = typename BasicJsonType::number_integer_t;
@@ -268,10 +273,9 @@ class lexer : public lexer_base<BasicJsonType>
   public:
     using token_type = typename lexer_base<BasicJsonType>::token_type;
 
-    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false, bool discard_number_values_ = false) noexcept
+    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false) noexcept
         : ia(std::move(adapter))
         , ignore_comments(ignore_comments_)
-        , discard_number_values(discard_number_values_)
     {
         // the token string of an error before the first token is everything
         // read so far
@@ -388,6 +392,8 @@ class lexer : public lexer_base<BasicJsonType>
     checks if it is inside the range. If a violation was detected, set up an
     error message and return false. Otherwise, return true.
 
+    @param[in] keep    whether the bytes are added to token_buffer (false for
+                       accept(), see scan())
     @param[in] ranges  list of integers; interpreted as list of pairs of
                        inclusive lower and upper bound, respectively
 
@@ -396,17 +402,18 @@ class lexer : public lexer_base<BasicJsonType>
 
     @return true if and only if no range violation was detected
     */
-    bool next_byte_in_range(std::initializer_list<char_int_type> ranges)
+    template<bool Keep>
+    bool next_byte_in_range(std::integral_constant<bool, Keep> keep, std::initializer_list<char_int_type> ranges)
     {
         JSON_ASSERT(ranges.size() == 2 || ranges.size() == 4 || ranges.size() == 6);
-        add(current);
+        add_string_char(keep, current);
 
         for (auto range = ranges.begin(); range != ranges.end(); ++range)
         {
             get();
             if (JSON_HEDLEY_LIKELY(*range <= current && current <= *(++range))) // NOLINT(bugprone-inc-dec-in-conditions)
             {
-                add(current);
+                add_string_char(keep, current);
             }
             else
             {
@@ -419,14 +426,16 @@ class lexer : public lexer_base<BasicJsonType>
     }
 
     /// contiguous input: bulk-append the run of ordinary characters and complete
-    /// well-formed UTF-8 sequences starting at the current read position, then
+    /// well-formed UTF-8 sequences starting at the current read position (only
+    /// skip it if @a keep is false), then
     /// read the first byte that needs individual handling (the closing quote, an
     /// escape, a control character, or an ill-formed UTF-8 byte) like get().
     /// That byte is taken from the buffer that was just scanned. Through get(),
     /// Apple Clang merged this read with the other get() calls of the scan
     /// function, which load the read position again right after it was stored
     /// (3% of json::accept() on jeopardy.json on Apple M1).
-    char_int_type get_after_string_run(std::true_type /*bulk*/)
+    template<bool Keep>
+    char_int_type get_after_string_run(std::true_type /*bulk*/, std::integral_constant<bool, Keep> keep)
     {
         // a pending unget must be consumed through the normal path first
         if (next_unget)
@@ -444,7 +453,7 @@ class lexer : public lexer_base<BasicJsonType>
         const std::size_t pos = lexer_string_bulk_run(data, remaining);
         if (pos != 0)
         {
-            token_buffer.append(reinterpret_cast<const typename string_t::value_type*>(data), pos);
+            append_string_run(keep, data, pos);
             bulk_consume(reinterpret_cast<const char*>(data), pos);
         }
         if (pos == remaining)
@@ -488,7 +497,8 @@ class lexer : public lexer_base<BasicJsonType>
     }
 
     /// streaming input: no bulk fast path
-    char_int_type get_after_string_run(std::false_type /*bulk*/)
+    template<bool Keep>
+    char_int_type get_after_string_run(std::false_type /*bulk*/, std::integral_constant<bool, Keep> /*keep*/)
     {
         return get();
     }
@@ -502,13 +512,18 @@ class lexer : public lexer_base<BasicJsonType>
     may contain \0 bytes), and token_buffer.size() is the number of bytes in the
     string.
 
+    @param[in] keep  whether the string is copied into token_buffer; if false
+                     (accept(), see scan()), it is only checked, with the same
+                     errors, and token_buffer stays empty
+
     @return token_type::value_string if string could be successfully scanned,
             token_type::parse_error otherwise
 
     @note In case of errors, variable error_message contains a textual
           description.
     */
-    token_type scan_string()
+    template<bool Keep>
+    token_type scan_string(std::integral_constant<bool, Keep> keep)
     {
         // reset token_buffer (ignore opening quote)
         reset();
@@ -520,7 +535,7 @@ class lexer : public lexer_base<BasicJsonType>
         {
             // bulk-consume ordinary characters from contiguous input, then
             // get the next character, the one that ends the run
-            switch (get_after_string_run(std::integral_constant<bool, bulk_scan>()))
+            switch (get_after_string_run(std::integral_constant<bool, bulk_scan>(), keep))
             {
                 // end of file while parsing the string
                 case char_traits<char_type>::eof():
@@ -542,35 +557,35 @@ class lexer : public lexer_base<BasicJsonType>
                     {
                         // quotation mark
                         case '\"':
-                            add('\"');
+                            add_string_char(keep, '\"');
                             break;
                         // reverse solidus
                         case '\\':
-                            add('\\');
+                            add_string_char(keep, '\\');
                             break;
                         // solidus
                         case '/':
-                            add('/');
+                            add_string_char(keep, '/');
                             break;
                         // backspace
                         case 'b':
-                            add('\b');
+                            add_string_char(keep, '\b');
                             break;
                         // form feed
                         case 'f':
-                            add('\f');
+                            add_string_char(keep, '\f');
                             break;
                         // line feed
                         case 'n':
-                            add('\n');
+                            add_string_char(keep, '\n');
                             break;
                         // carriage return
                         case 'r':
-                            add('\r');
+                            add_string_char(keep, '\r');
                             break;
                         // tab
                         case 't':
-                            add('\t');
+                            add_string_char(keep, '\t');
                             break;
 
                         // unicode escapes
@@ -638,10 +653,7 @@ class lexer : public lexer_base<BasicJsonType>
                             JSON_ASSERT(0x00 <= codepoint && codepoint <= 0x10FFFF);
 
                             // translate codepoint into bytes
-                            encode_utf8(static_cast<std::uint32_t>(codepoint), [this](std::uint32_t byte)
+                            add_codepoint(keep, codepoint);
-                            {
-                                add(static_cast<char_int_type>(byte));
-                            });
 
                             break;
                         }
@@ -824,7 +836,7 @@ class lexer : public lexer_base<BasicJsonType>
                 case 0x7E:
                 case 0x7F:
                 {
-                    add(current);
+                    add_string_char(keep, current);
                     break;
                 }
 
@@ -860,7 +872,7 @@ class lexer : public lexer_base<BasicJsonType>
                 case 0xDE:
                 case 0xDF:
                 {
-                    if (JSON_HEDLEY_UNLIKELY(!next_byte_in_range({0x80, 0xBF})))
+                    if (JSON_HEDLEY_UNLIKELY(!next_byte_in_range(keep, {0x80, 0xBF})))
                     {
                         return token_type::parse_error;
                     }
@@ -870,7 +882,7 @@ class lexer : public lexer_base<BasicJsonType>
                 // U+0800..U+0FFF: bytes E0 A0..BF 80..BF
                 case 0xE0:
                 {
-                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0xA0, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range(keep, {0xA0, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -894,7 +906,7 @@ class lexer : public lexer_base<BasicJsonType>
                 case 0xEE:
                 case 0xEF:
                 {
-                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x80, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range(keep, {0x80, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -904,7 +916,7 @@ class lexer : public lexer_base<BasicJsonType>
                 // U+D000..U+D7FF: bytes ED 80..9F 80..BF
                 case 0xED:
                 {
-                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x80, 0x9F, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range(keep, {0x80, 0x9F, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -914,7 +926,7 @@ class lexer : public lexer_base<BasicJsonType>
                 // U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
                 case 0xF0:
                 {
-                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x90, 0xBF, 0x80, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range(keep, {0x90, 0xBF, 0x80, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -926,7 +938,7 @@ class lexer : public lexer_base<BasicJsonType>
                 case 0xF2:
                 case 0xF3:
                 {
-                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range(keep, {0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -936,7 +948,7 @@ class lexer : public lexer_base<BasicJsonType>
                 // U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
                 case 0xF4:
                 {
-                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x80, 0x8F, 0x80, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range(keep, {0x80, 0x8F, 0x80, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -1427,7 +1439,7 @@ scan_number_done:
     token_type convert_number(token_type number_type, std::size_t mantissa_end)
     {
         // accept() only needs to know whether the input is valid, so it sets
-        // discard_number_values (see json.hpp), and an integer token whose
+        // discard_values (see json.hpp), and an integer token whose
         // digit count shows that it fits is reported without calling
         // convert_integer(). A number with up to 18 digits always fits into
         // both std::uint64_t and std::int64_t (18 nines is about 1e18, below
@@ -1442,7 +1454,7 @@ scan_number_done:
         // json_sax_acceptor, whose number callbacks discard their argument and
         // return true, and the parser rejects neither integers nor finite
         // floats. value_unsigned/value_integer are left unset here, so a caller
-        // that reads the converted value must not set discard_number_values.
+        // that reads the converted value must not set discard_values.
         //
         // On contiguous input, scan_number_bulk_contiguous() converts integer
         // tokens itself and does not pass them to this function, unless
@@ -1450,7 +1462,7 @@ scan_number_done:
         // reached for input without bulk access (e.g. streams), with
         // JSON_DIAGNOSTIC_POSITIONS, or when scan_number_bulk_contiguous()
         // falls back to scan_number().
-        if (discard_number_values)
+        if (discard_values())
         {
             constexpr std::size_t safe_digit_count = 18;
             if (number_type == token_type::value_unsigned && token_buffer.size() <= safe_digit_count)
@@ -1701,7 +1713,7 @@ scan_number_done:
         // w < 10^19, so a value below 10^max_exponent10 cannot overflow, and a
         // value that underflows is a finite number as well. Only a token that
         // may overflow has to be converted to find out.
-        if (JSON_HEDLEY_UNLIKELY(discard_number_values && s.exponent + 19 <= std::numeric_limits<number_float_t>::max_exponent10))
+        if (JSON_HEDLEY_UNLIKELY(discard_values() && s.exponent + 19 <= std::numeric_limits<number_float_t>::max_exponent10))
         {
             value_float = 0;
             return true;
@@ -2033,6 +2045,34 @@ scan_number_done:
         token_buffer.push_back(static_cast<typename string_t::value_type>(c));
     }
 
+    /// add a character of a string token; accept() checks the string but does
+    /// not keep its value (@a keep is false)
+    void add_string_char(std::true_type /*keep*/, char_int_type c)
+    {
+        token_buffer.push_back(static_cast<typename string_t::value_type>(c));
+    }
+
+    static void add_string_char(std::false_type /*keep*/, char_int_type /*c*/) noexcept {}
+
+    /// add the UTF-8 bytes of a code point from a \\u escape to a string token
+    void add_codepoint(std::true_type /*keep*/, int codepoint)
+    {
+        encode_utf8(static_cast<std::uint32_t>(codepoint), [this](std::uint32_t byte)
+        {
+            add(static_cast<char_int_type>(byte));
+        });
+    }
+
+    static void add_codepoint(std::false_type /*keep*/, int /*codepoint*/) noexcept {}
+
+    /// append a run of ordinary string characters (see get_after_string_run())
+    void append_string_run(std::true_type /*keep*/, const unsigned char* data, std::size_t n)
+    {
+        token_buffer.append(reinterpret_cast<const typename string_t::value_type*>(data), n);
+    }
+
+    static void append_string_run(std::false_type /*keep*/, const unsigned char* /*data*/, std::size_t /*n*/) noexcept {}
+
   public:
     /////////////////////
     // value getters
@@ -2427,7 +2467,9 @@ scan_number_done:
 
             // string
             case '\"':
-                return scan_string();
+                // accept() (DiscardValues) checks strings without copying them
+                // into token_buffer
+                return scan_string(keep_strings {});
 
             // number
             case '-':
@@ -2512,11 +2554,19 @@ scan_number_done:
     std::size_t decimal_point_position = std::string::npos;
 
     /// whether the caller only needs the token types and never looks at the
-    /// converted numeric values; set only by accept(), which parses through
+    /// values of number and string tokens; DiscardValues, set only by accept(), which parses
-    /// json_sax_acceptor. When set, convert_number() skips converting integer
+    /// through json_sax_acceptor. When set, convert_number() skips converting
-    /// tokens whose digit count guarantees that they fit into 64 bits (see
+    /// integer tokens whose digit count guarantees that they fit into 64 bits
-    /// there)
+    /// (see there), floats are converted only when they may overflow (see
-    const bool discard_number_values = false;
+    /// convert_accumulated_float()), and strings are checked without being
+    /// copied into token_buffer (see scan())
+    static bool discard_values() noexcept
+    {
+        return DiscardValues;
+    }
+
+    /// the tag of scan_string(): whether string tokens are kept
+    using keep_strings = typename std::conditional<DiscardValues, std::false_type, std::true_type>::type;
 };
 
 }  // namespace detail

include/nlohmann/detail/input/parser.hpp

@@ -72,14 +72,14 @@ This class implements a parser for JSON text. Nested arrays and objects are trac
 stack instead of recursion, so deeply nested input does not exhaust the call stack, and what is read
 is reported as SAX events.
 */
-template<typename BasicJsonType, typename InputAdapterType>
+template<typename BasicJsonType, typename InputAdapterType, bool DiscardValues = false>
 class parser
 {
     using number_integer_t = typename BasicJsonType::number_integer_t;
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
     using number_float_t = typename BasicJsonType::number_float_t;
     using string_t = typename BasicJsonType::string_t;
-    using lexer_t = lexer<BasicJsonType, InputAdapterType>;
+    using lexer_t = lexer<BasicJsonType, InputAdapterType, DiscardValues>;
     using token_type = typename lexer_t::token_type;
 
   public:
@@ -88,10 +88,9 @@ class parser
                     parser_callback_t<BasicJsonType> cb = nullptr,
                     const bool allow_exceptions_ = true,
                     const bool ignore_comments = false,
-                    const bool ignore_trailing_commas_ = false,
+                    const bool ignore_trailing_commas_ = false)
-                    const bool discard_number_values_ = false)
         : callback(std::move(cb))
-        , m_lexer(std::move(adapter), ignore_comments, discard_number_values_)
+        , m_lexer(std::move(adapter), ignore_comments)
         , allow_exceptions(allow_exceptions_)
         , ignore_trailing_commas(ignore_trailing_commas_)
     {

include/nlohmann/detail/input/simd_scan.hpp

@@ -322,6 +322,78 @@ JSON_SCAN_SSSE3_TARGET JSON_HEDLEY_NEVER_INLINE inline bool vector_utf8_run(cons
     block_out = block;
     return false;
 }
+
+/*!
+@brief skip 16-byte blocks of well-formed UTF-8 at p (a character boundary)
+
+Like vector_utf8_run, but quotes, backslashes, and control characters are
+ordinary characters. Returns the start of the first block in which the check
+found an error (which may belong to a sequence begun in the block before) or
+where fewer than 16 bytes are left; a sequence may be cut at that point, so the
+caller resumes at its start, one sequence at a time.
+*/
+JSON_SCAN_SSSE3_TARGET JSON_HEDLEY_NEVER_INLINE inline const unsigned char* vector_utf8_valid_blocks(const unsigned char* block, const unsigned char* e) noexcept
+{
+    using lookup = utf8_lookup4<>;
+#if JSON_SCAN_NEON
+    const uint8x16_t t1h = vld1q_u8(lookup::byte_1_high.data());
+    const uint8x16_t t1l = vld1q_u8(lookup::byte_1_low.data());
+    const uint8x16_t t2h = vld1q_u8(lookup::byte_2_high.data());
+    uint8x16_t prev = vdupq_n_u8(0);
+    while (e - block >= 16)
+    {
+        const uint8x16_t in = vld1q_u8(block);
+        if (vmaxvq_u8(vorrq_u8(in, prev)) < 0x80)
+        {
+            // ASCII here, and no sequence from the block before to finish
+            prev = in;
+            block += 16;
+            continue;
+        }
+        const uint8x16_t prev1 = vextq_u8(prev, in, 15);
+        const uint8x16_t sc = vandq_u8(vandq_u8(vqtbl1q_u8(t1h, vshrq_n_u8(prev1, 4)), vqtbl1q_u8(t1l, vandq_u8(prev1, vdupq_n_u8(0x0F)))), vqtbl1q_u8(t2h, vshrq_n_u8(in, 4)));
+        const uint8x16_t must23 = vorrq_u8(vqsubq_u8(vextq_u8(prev, in, 14), vdupq_n_u8(0xE0 - 0x80)), vqsubq_u8(vextq_u8(prev, in, 13), vdupq_n_u8(0xF0 - 0x80)));
+        const uint8x16_t err = veorq_u8(vandq_u8(must23, vdupq_n_u8(0x80)), sc);
+        if (vmaxvq_u8(err) != 0)
+        {
+            break;
+        }
+        prev = in;
+        block += 16;
+    }
+#else
+    const __m128i t1h = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_1_high.data()))); // NOLINT(bugprone-casting-through-void)
+    const __m128i t1l = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_1_low.data()))); // NOLINT(bugprone-casting-through-void)
+    const __m128i t2h = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_2_high.data()))); // NOLINT(bugprone-casting-through-void)
+    const __m128i nibble = _mm_set1_epi8(0x0F);
+    const __m128i zero = _mm_setzero_si128();
+    __m128i prev = zero;
+    while (e - block >= 16)
+    {
+        const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(block))); // NOLINT(bugprone-casting-through-void)
+        if (_mm_movemask_epi8(_mm_or_si128(in, prev)) == 0)
+        {
+            prev = in;
+            block += 16;
+            continue;
+        }
+        const __m128i prev1 = _mm_alignr_epi8(in, prev, 15);
+        const __m128i sc = _mm_and_si128(_mm_and_si128(_mm_shuffle_epi8(t1h, _mm_and_si128(_mm_srli_epi16(prev1, 4), nibble)),
+                                         _mm_shuffle_epi8(t1l, _mm_and_si128(prev1, nibble))),
+                                         _mm_shuffle_epi8(t2h, _mm_and_si128(_mm_srli_epi16(in, 4), nibble)));
+        const __m128i must23 = _mm_or_si128(_mm_subs_epu8(_mm_alignr_epi8(in, prev, 14), _mm_set1_epi8(0xE0 - 0x80)),
+                                            _mm_subs_epu8(_mm_alignr_epi8(in, prev, 13), _mm_set1_epi8(0xF0 - 0x80)));
+        const __m128i err = _mm_xor_si128(_mm_and_si128(must23, _mm_set1_epi8(static_cast<char>(-128))), sc);
+        if (_mm_movemask_epi8(_mm_cmpeq_epi8(err, zero)) != 0xFFFF)
+        {
+            break;
+        }
+        prev = in;
+        block += 16;
+    }
+#endif
+    return block;
+}
 #endif
 
 }  // namespace detail

include/nlohmann/detail/input/string_scan.hpp

@@ -90,6 +90,34 @@ JSON_HEDLEY_ALWAYS_INLINE std::size_t find_string_special(const unsigned char* d
     return n;
 }
 
+// return the index of the first 0x00 byte in [data, data+n), or n if there is
+// none; scans 8 bytes at a time (BSON's C-style strings)
+JSON_HEDLEY_ALWAYS_INLINE std::size_t find_zero_byte(const unsigned char* data, std::size_t n) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        const std::uint64_t v = read_eight_bytes(data + i);
+        const std::uint64_t zero = (v - ones) & ~v & high;
+        if (zero != 0)
+        {
+            // the lowest flagged byte is the first zero byte (see
+            // find_string_special())
+            return i + (static_cast<std::size_t>(count_trailing_zeros(zero)) / 8);
+        }
+    }
+    for (; i < n; ++i)
+    {
+        if (data[i] == 0x00)
+        {
+            return i;
+        }
+    }
+    return n;
+}
+
 // classify a byte as one the serializer must NOT copy verbatim when
 // ensure_ascii is requested: the closing quote, an escape, a control character
 // (< 0x20), DEL (0x7F), or any non-ASCII byte (>= 0x80). Everything else -
@@ -236,6 +264,64 @@ inline std::size_t valid_utf8_prefix(const unsigned char* data, std::size_t n) n
     return pos;
 }
 
+/*!
+@brief whether [data, data+n) is valid UTF-8, for checking whole strings
+
+The same answer as valid_utf8_prefix(data, n) == n. Short ASCII strings, the
+most common keys and values, are decided in one test, and long strings are
+checked 16 bytes at a time where the vector check is available.
+*/
+inline bool valid_utf8_string(const unsigned char* data, std::size_t n) noexcept
+{
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    if (n <= 16)
+    {
+        // two overlapping words cover 8 to 16 bytes, one partial word fewer
+        std::uint64_t first = 0;
+        std::uint64_t last = 0;
+        if (n >= 8)
+        {
+            std::memcpy(&first, data, sizeof(first));
+            std::memcpy(&last, data + n - 8, sizeof(last));
+        }
+        else if (n != 0)
+        {
+            std::memcpy(&first, data, n);
+        }
+        if (((first | last) & high) == 0)
+        {
+            return true;
+        }
+    }
+#if JSON_SCAN_VECTOR_UTF8
+    else if (n >= 32
+#if JSON_SCAN_SSSE3_DISPATCH
+             && cpu_has_ssse3()
+#endif
+            )
+    {
+        const unsigned char* block = vector_utf8_valid_blocks(data, data + n);
+        // the rest from the start of a sequence that may be cut at block
+        for (int i = 1; i <= 3 && block - i >= data; ++i)
+        {
+            const unsigned char c = block[-i];
+            if (c < 0x80)
+            {
+                break;
+            }
+            if (c >= 0xC0)
+            {
+                block -= i;
+                break;
+            }
+        }
+        const auto checked = static_cast<std::size_t>(block - data);
+        return checked + valid_utf8_prefix(block, n - checked) == n;
+    }
+#endif
+    return valid_utf8_prefix(data, n) == n;
+}
+
 #if JSON_SCAN_VECTOR_UTF8
 /// the end of scan_string_vector from block, where the vector loop stopped
 /// (ill-formed UTF-8, or fewer than 16 bytes left): one byte or sequence at a

include/nlohmann/detail/macro_scope.hpp

@@ -347,7 +347,7 @@
             return ej_pair.second == j;                                                         \
         });                                                                                     \
         if (it != std::end(m)) e = it->first;                                                   \
-        else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(nlohmann::detail::exception_id::value_out_of_range, nlohmann::detail::concat("enum value out of range for " #ENUM_TYPE ": ", nlohmann::detail::from_json_dump(j)), nlohmann::detail::exception_context(j))); \
+        else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(nlohmann::detail::exception_id::value_out_of_range, nlohmann::detail::concat(nlohmann::detail::exception_prefix(j), "enum value out of range for " #ENUM_TYPE ": ", nlohmann::detail::from_json_dump(j)), nlohmann::detail::exception_context(j))); \
     }
 
 // Ugly macros to avoid uglier copy-paste when specializing basic_json. They

include/nlohmann/detail/output/binary_writer.hpp

@@ -2088,7 +2088,8 @@ class binary_writer
         /// arrays: the first index with one more digit; only maintained by
         /// @ref calc_bson_sizes
         std::uint64_t index_boundary = 10;
-        /// @ref calc_bson_sizes only: where its size goes in the table
+        /// @ref calc_bson_sizes: where its size goes in the table; @ref
+        /// write_bson_document_single_pass: the position of its size field
         std::size_t size_slot;
         /// @ref calc_bson_sizes only: the size of its entries seen so far
         std::size_t entries_size = 0;
@@ -2339,6 +2340,199 @@ class binary_writer
         }
     }
 
+    template<typename SinkType>
+    using sink_written_t = decltype(std::declval<const SinkType&>().written());
+
+    /// whether every integer fits the 64 bits BSON has, so that writing an
+    /// array of numbers needs no range check
+    static constexpr bool bson_integers_fit_64_bits =
+        std::numeric_limits<typename BasicJsonType::number_integer_t>::is_specialized
+        && std::numeric_limits<typename BasicJsonType::number_integer_t>::digits <= std::numeric_limits<std::int64_t>::digits
+        && std::numeric_limits<typename BasicJsonType::number_unsigned_t>::is_specialized
+        && std::numeric_limits<typename BasicJsonType::number_unsigned_t>::digits <= std::numeric_limits<std::uint64_t>::digits;
+
+    /*!
+    @brief whether BSON documents can be written in a single pass: the sink
+           can overwrite what it has written (output_vector_sink), and
+           @ref bson_integers_fit_64_bits
+    */
+    using bson_single_pass_sink = conjunction<is_detected<sink_written_t, OutputSinkType>, std::integral_constant<bool, bson_integers_fit_64_bits>>;
+
+    /// write a placeholder for the size of an object or array whose entries
+    /// follow; @return its position, for @ref close_bson_container
+    std::size_t write_bson_size_placeholder()
+    {
+        const std::size_t pos = oa.written();
+        // zero in any byte order
+        const std::array<CharType, sizeof(std::int32_t)> zero{};
+        oa.write_characters(zero.data(), zero.size());
+        return pos;
+    }
+
+    /// end the object or array whose size is at @a pos and write its size
+    /// there: everything from that field to the terminating null byte
+    /// @return false (and the size is not written) if it does not fit
+    bool close_bson_container(const std::size_t pos)
+    {
+        oa.write_character(to_char_type(0x00));
+        const std::size_t size = oa.written() - pos;
+        if (JSON_HEDLEY_UNLIKELY(!value_in_range_of<std::int32_t>(size)))
+        {
+            return false;
+        }
+        const auto le_size = static_cast<std::uint32_t>(size);
+        oa.overwrite(pos, is_little_endian ? le_size : byteswap(le_size));
+        return true;
+    }
+
+    /*!
+    @brief check the value @a j of a BSON entry as @ref calc_bson_value_size
+           does, for @ref write_bson_document_single_pass
+    @return at least the size of the value
+    A number, boolean, or null needs no check there (its integers have at most
+    64 bits) and has at most 8 characters; a discarded value is rejected with
+    the same exception when it is written.
+    */
+    std::size_t check_bson_value(const BasicJsonType& j)
+    {
+        return (j.is_string() || j.is_binary()) ? calc_bson_value_size(j) : 8;
+    }
+
+    /// whether an entry of @a entry_size characters keeps the document that
+    /// begins at @a start, closed by @a open_containers null bytes, within
+    /// the 32-bit size of BSON
+    bool bson_entry_fits(const std::size_t start, const std::size_t entry_size, const std::size_t open_containers) const noexcept
+    {
+        const auto limit = static_cast<std::size_t>((std::numeric_limits<std::int32_t>::max)());
+        const std::size_t written = oa.written() - start;
+        return written <= limit && entry_size <= limit - written && open_containers <= limit - written - entry_size;
+    }
+
+    /*!
+    @brief Serializes the JSON object @a document as a BSON document in a
+           single pass, writing the size of each object and array once it is
+           complete
+
+    Checks every key and value as @ref calc_bson_sizes does, in the same
+    order, so the same exception is thrown; the output written up to then is
+    discarded with the vector it was written to.
+
+    @return false as soon as the document or a string, binary value, object,
+            or array in it would be larger than the 32-bit BSON sizes allow;
+            nothing large has been written then, and the caller writes the
+            document in two passes, which reports that error
+    */
+    template<typename SinkType = OutputSinkType, typename std::enable_if<is_detected<sink_written_t, SinkType>::value, int>::type = 0>
+    bool write_bson_document_single_pass(const BasicJsonType& document)
+    {
+        const std::size_t start = oa.written();
+        // the object or array whose entries are being written (with the
+        // position of its size), and the ones it is in
+        bson_frame current(&document, write_bson_size_placeholder());
+        std::vector<bson_frame> parents;
+
+        while (true)
+        {
+            const BasicJsonType* nested = nullptr;
+            std::size_t nested_size_pos = 0;
+            if (current.value->is_object())
+            {
+                const auto& object = *current.value->m_data.m_value.object;
+                while (nested == nullptr && current.member != object.cend())
+                {
+                    const auto& el = *current.member;
+                    ++current.member;
+                    const std::size_t header_size = calc_bson_entry_header_size(el.first, el.second);
+                    const std::size_t value_size = el.second.is_structured() ? 0 : check_bson_value(el.second);
+                    if (JSON_HEDLEY_UNLIKELY(!bson_entry_fits(start, header_size + value_size, parents.size() + 1)))
+                    {
+                        return false;
+                    }
+                    if (el.second.is_structured())
+                    {
+                        write_bson_entry_header(el.first, el.second.is_object() ? 0x03 : 0x04);
+                        nested_size_pos = write_bson_size_placeholder();
+                        nested = &el.second;
+                    }
+                    else
+                    {
+                        write_bson_value(el.first, el.second);
+                    }
+                }
+            }
+            else
+            {
+                const auto& array = *current.value->m_data.m_value.array;
+                while (nested == nullptr && current.index < array.size())
+                {
+                    if (is_bson_fixed_size(array[current.index]))
+                    {
+                        write_bson_array_fixed_entries(current);
+                        if (current.index == array.size())
+                        {
+                            break;
+                        }
+                    }
+
+                    // a string, binary value, object or array
+                    const BasicJsonType& el = array[current.index];
+                    const string_t index_name(current.index_name.data(), current.index_name_size);
+                    current.next_index();
+                    const std::size_t value_size = el.is_structured() ? 0 : check_bson_value(el);
+                    if (JSON_HEDLEY_UNLIKELY(!bson_entry_fits(start, 2 + index_name.size() + value_size, parents.size() + 1)))
+                    {
+                        return false;
+                    }
+                    if (el.is_structured())
+                    {
+                        write_bson_entry_header(index_name, el.is_object() ? 0x03 : 0x04);
+                        nested_size_pos = write_bson_size_placeholder();
+                        nested = &el;
+                    }
+                    else
+                    {
+                        write_bson_value(index_name, el);
+                    }
+                }
+            }
+
+            if (nested != nullptr)
+            {
+                if (nested->is_array())
+                {
+                    // an array of booleans, numbers and null is written without a frame on the stack
+                    bson_frame leaf(nested, nested_size_pos);
+                    write_bson_array_fixed_entries(leaf);
+                    if (leaf.index == nested->m_data.m_value.array->size())
+                    {
+                        if (JSON_HEDLEY_UNLIKELY(!close_bson_container(nested_size_pos)))
+                        {
+                            return false;
+                        }
+                        continue;
+                    }
+                    parents.push_back(std::move(current));
+                    current = std::move(leaf);
+                    continue;
+                }
+                parents.push_back(std::move(current));
+                current = bson_frame(nested, nested_size_pos);
+                continue;
+            }
+
+            if (JSON_HEDLEY_UNLIKELY(!close_bson_container(current.size_slot)))
+            {
+                return false;
+            }
+            if (parents.empty())
+            {
+                return true;
+            }
+            current = std::move(parents.back());
+            parents.pop_back();
+        }
+    }
+
     /*!
     @brief Serializes the JSON object @a document as a BSON document
 
@@ -2350,6 +2544,39 @@ class binary_writer
     @pre       document.type() == value_t::object
     */
     void write_bson_document(const BasicJsonType& document)
+    {
+        write_bson_document(document, bson_single_pass_sink());
+    }
+
+    /// the sink can overwrite: one pass, unless the error handler replaces or
+    /// drops ill-formed UTF-8, which changes the sizes the checks compute
+    void write_bson_document(const BasicJsonType& document, std::true_type /*single_pass*/)
+    {
+        const std::size_t start = oa.written();
+        if ((error_handler == error_handler_t::keep || error_handler == error_handler_t::strict)
+                && write_bson_document_single_pass(document))
+        {
+            return;
+        }
+        // a length does not fit: start over, so that it is reported as the
+        // two passes report it, before anything is written
+        oa.rewind(start);
+        write_bson_document_two_pass(document);
+    }
+
+    void write_bson_document(const BasicJsonType& document, std::false_type /*single_pass*/)
+    {
+        write_bson_document_two_pass(document);
+    }
+
+    /*!
+    @brief Serializes the JSON object @a document as a BSON document: the
+           sizes of all objects and arrays first, then the entries
+
+    @param[in] document  the JSON object to serialize
+    @pre       document.type() == value_t::object
+    */
+    void write_bson_document_two_pass(const BasicJsonType& document)
     {
         std::vector<std::size_t> nested_sizes;
         const std::size_t document_size = calc_bson_sizes(document, nested_sizes);
@@ -3080,6 +3307,25 @@ class binary_writer
         }
     }
 
+    /// write the head and the characters of @a value, at most
+    /// max_text_in_reservation of them, in one reservation
+    JSON_HEDLEY_ALWAYS_INLINE void write_cbor_string_reserved(const string_t& value)
+    {
+        CharType* const out = oa.reserve(value.size() + 2);
+        CharType* p = out;
+        if (value.size() <= 0x17)
+        {
+            *p++ = to_char_type(static_cast<std::uint8_t>(0x60 + value.size()));
+        }
+        else
+        {
+            *p++ = to_char_type(0x78);
+            *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
+        }
+        copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
+        oa.commit(static_cast<std::size_t>(p - out) + value.size());
+    }
+
     /*!
     @brief write a CBOR text string
 
@@ -3101,19 +3347,7 @@ class binary_writer
             // the string is written as it is: head and characters in one reservation
             if (JSON_HEDLEY_LIKELY(value.size() <= max_text_in_reservation))
             {
-                CharType* const out = oa.reserve(value.size() + 2);
+                write_cbor_string_reserved(value);
-                CharType* p = out;
-                if (value.size() <= 0x17)
-                {
-                    *p++ = to_char_type(static_cast<std::uint8_t>(0x60 + value.size()));
-                }
-                else
-                {
-                    *p++ = to_char_type(0x78);
-                    *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
-                }
-                copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
-                oa.commit(static_cast<std::size_t>(p - out) + value.size());
                 return;
             }
         }
@@ -3127,6 +3361,13 @@ class binary_writer
     JSON_HEDLEY_NEVER_INLINE
     void write_cbor_checked_string(const string_t& value, const BasicJsonType& context)
     {
+        if (error_handler == error_handler_t::strict && value.size() <= max_text_in_reservation)
+        {
+            check_utf8(value, context);
+            write_cbor_string_reserved(value);
+            return;
+        }
+
         string_t storage;
         const string_t& sanitized = sanitize_utf8_for_write(value, context, storage);
 
@@ -3141,6 +3382,27 @@ class binary_writer
     // MsgPack //
     /////////////
 
+    /// write the head and the characters of @a value, at most
+    /// max_text_in_reservation of them, in one reservation
+    JSON_HEDLEY_ALWAYS_INLINE void write_msgpack_string_reserved(const string_t& value)
+    {
+        CharType* const out = oa.reserve(value.size() + 2);
+        CharType* p = out;
+        if (value.size() <= 31)
+        {
+            // fixstr
+            *p++ = to_char_type(static_cast<std::uint8_t>(0xA0 | value.size()));
+        }
+        else
+        {
+            // str 8
+            *p++ = to_char_type(0xD9);
+            *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
+        }
+        copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
+        oa.commit(static_cast<std::size_t>(p - out) + value.size());
+    }
+
     /*!
     @brief write a MessagePack str
 
@@ -3158,21 +3420,7 @@ class binary_writer
             // the string is written as it is: head and characters in one reservation
             if (JSON_HEDLEY_LIKELY(value.size() <= max_text_in_reservation))
             {
-                CharType* const out = oa.reserve(value.size() + 2);
+                write_msgpack_string_reserved(value);
-                CharType* p = out;
-                if (value.size() <= 31)
-                {
-                    // fixstr
-                    *p++ = to_char_type(static_cast<std::uint8_t>(0xA0 | value.size()));
-                }
-                else
-                {
-                    // str 8
-                    *p++ = to_char_type(0xD9);
-                    *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
-                }
-                copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
-                oa.commit(static_cast<std::size_t>(p - out) + value.size());
                 return;
             }
         }
@@ -3185,6 +3433,13 @@ class binary_writer
     JSON_HEDLEY_NEVER_INLINE
     void write_msgpack_checked_string(const string_t& value, const BasicJsonType& context)
     {
+        if (error_handler == error_handler_t::strict && value.size() <= max_text_in_reservation)
+        {
+            check_utf8(value, context);
+            write_msgpack_string_reserved(value);
+            return;
+        }
+
         string_t storage;
         const string_t& sanitized = sanitize_utf8_for_write(value, context, storage);
 
@@ -4794,10 +5049,9 @@ class binary_writer
     static void check_utf8(const string_t& s, const BasicJsonType& context)
     {
         const auto* data = reinterpret_cast<const unsigned char*>(s.data());
-        const std::size_t valid = valid_utf8_prefix(data, s.size());
+        if (JSON_HEDLEY_UNLIKELY(!valid_utf8_string(data, s.size())))
-        if (JSON_HEDLEY_UNLIKELY(valid != s.size()))
         {
-            throw_invalid_utf8(data, valid, context);
+            throw_invalid_utf8(data, valid_utf8_prefix(data, s.size()), context);
         }
     }
 

include/nlohmann/detail/output/output_adapters.hpp

@@ -11,6 +11,7 @@
 #include <algorithm> // max
 #include <array> // array
 #include <cstddef> // size_t
+#include <cstdint> // uint32_t
 #include <cstring> // memcpy
 #include <memory> // shared_ptr, make_shared
 #include <string> // basic_string
@@ -227,6 +228,31 @@ class output_vector_sink
     void flush() noexcept
     {}
 
+    /// the number of characters written so far, the position of the next one
+    std::size_t written() const noexcept
+    {
+        return position();
+    }
+
+    /// @brief replace the 4 bytes written before at position @a pos with
+    ///        those of @a n, in the byte order of the machine
+    ///
+    /// Lets a writer put a length in front of data it has written since, such
+    /// as the size of a BSON document, without computing it in advance.
+    void overwrite(const std::size_t pos, const std::uint32_t n) noexcept
+    {
+        static_assert(sizeof(CharType) == 1, "overwrite() writes bytes");
+        JSON_ASSERT(pos + sizeof(n) <= position());
+        std::memcpy(v->data() + pos, &n, sizeof(n));
+    }
+
+    /// drop the characters written from position @a pos on
+    void rewind(const std::size_t pos) noexcept
+    {
+        JSON_ASSERT(pos <= position());
+        cursor = v->data() + pos;
+    }
+
   private:
     /// number of characters of *v written so far
     std::size_t position() const noexcept

include/nlohmann/detail/output/serializer.hpp

@@ -1977,6 +1977,23 @@ class serializer
             return;
         }
 
+        // 17 to 20 digits: the first one to four, then twice eight
+        if (magnitude_fits_64_bits(abs_value, std::integral_constant<bool, magnitude_has_at_most_64_bits>()))
+        {
+            const auto value = static_cast<std::uint64_t>(abs_value);
+            const std::uint64_t top = value / 10000000000000000u; // 1 to 1844
+            const std::uint64_t low16 = value - (top * 10000000000000000u);
+            const std::uint64_t middle = low16 / 100000000u;
+            const std::uint64_t first = dtoa_impl::eight_digit_bytes(top);
+            const auto leading = static_cast<unsigned>(count_leading_zeros(first) / 8); // (first is not 0)
+            char* const p = buffer_ptr + n_chars;
+            dtoa_impl::store_msb_first(p, (first << (8 * leading)) + 0x3030303030303030u);
+            dtoa_impl::store_msb_first(p + 8 - leading, dtoa_impl::eight_digit_bytes(middle) + 0x3030303030303030u);
+            dtoa_impl::store_msb_first(p + 16 - leading, dtoa_impl::eight_digit_bytes(low16 - (middle * 100000000u)) + 0x3030303030303030u);
+            write_buffer_pos += n_chars + 24 - leading;
+            return;
+        }
+
         n_chars += count_digits(abs_value);
 
         // spare 1 byte for '\0'
@@ -2122,6 +2139,23 @@ class serializer
         }
     }
 
+    /// whether every number_magnitude_t fits 64 bits
+    static constexpr bool magnitude_has_at_most_64_bits = std::numeric_limits<number_magnitude_t>::is_specialized
+        && std::numeric_limits<number_magnitude_t>::digits <= 64;
+
+    /// whether @a x fits 64 bits: always if number_magnitude_t has at most
+    /// 64 bits (selected by type, as the comparison would be reported as
+    /// always true), else compared
+    static bool magnitude_fits_64_bits(const number_magnitude_t& /*unused*/, std::true_type /*unused*/) noexcept
+    {
+        return true;
+    }
+
+    static bool magnitude_fits_64_bits(const number_magnitude_t& x, std::false_type /*unused*/) noexcept
+    {
+        return x <= 18446744073709551615u;
+    }
+
     /*
      * Helper function for dump_integer
      *

include/nlohmann/detail/view/builder.hpp

@@ -69,7 +69,8 @@ struct parse_failure
 };
 
 /// FloatType: the number_float_t of the document, whose overflow parse() rejects
-template<typename FloatType, bool Comments, bool TrailingCommas, bool NulIsEnd, bool Sentinel>
+/// Store: false for accept(): the grammar, number, string and UTF-8 checks run as for parse(), but no node is written
+template<typename FloatType, bool Comments, bool TrailingCommas, bool NulIsEnd, bool Sentinel, bool Store>
 class builder
 {
   public:
@@ -245,11 +246,87 @@ class builder
         return p;
     }
 
+    /// the string from p, the first backslash, control character, ill-formed UTF-8 byte, or the end, checked and not
+    /// decoded (accept() stores nothing, so the arena is not written): the checks, errors and error positions of
+    /// slow_string(), for everything up to the closing quote
+    NLOHMANN_VIEW_NOINLINE decoded check_string(const unsigned char* p)
+    {
+        const unsigned char* const end = m_end;
+        for (;;)
+        {
+            if (p == end)
+            {
+                return failed(error_code::string_missing_quote, p);
+            }
+            const unsigned char c = *p;
+            if (c == '"')
+            {
+                ++p;
+                return decoded{p, 0, 0};
+            }
+            if (c != '\\')
+            {
+                return failed(c < 0x20 ? error_code::string_control_character : error_code::string_utf8, p);
+            }
+            ++p;
+            if (p == end)
+            {
+                return failed(error_code::string_missing_quote, p);
+            }
+            const unsigned char d = *p++;
+            if (d == 'u')
+            {
+                const int cp = hex4(p); // (moves p past the four digits)
+                if (NLOHMANN_VIEW_UNLIKELY(cp < 0))
+                {
+                    return failed(error_code::string_unicode_hex, p);
+                }
+                if (NLOHMANN_VIEW_UNLIKELY((cp & 0xF800) == 0xD800)) // a surrogate
+                {
+                    if (cp >= 0xDC00)
+                    {
+                        return failed(error_code::string_surrogate_low, p);
+                    }
+                    if (end - p < 2 || p[0] != '\\' || p[1] != 'u')
+                    {
+                        return failed(error_code::string_surrogate_high, p);
+                    }
+                    p += 2;
+                    const int lo = hex4(p); // (moves p past the four digits)
+                    if (lo < 0)
+                    {
+                        return failed(error_code::string_unicode_hex, p);
+                    }
+                    if (lo < 0xDC00 || lo > 0xDFFF)
+                    {
+                        return failed(error_code::string_surrogate_high, p);
+                    }
+                }
+            }
+            else if (!(d == '"' || d == '\\' || d == '/' || d == 'b' || d == 'f' || d == 'n' || d == 'r' || d == 't'))
+            {
+                --p;
+                return failed(error_code::string_escape, p);
+            }
+            if (p != end && *p == '\\')
+            {
+                continue; // (escapes in a row: no run of text between them)
+            }
+            p = scan_string_run(p, end); // the text up to the next backslash, quote, control character, or ill-formed UTF-8
+        }
+    }
+
     /// s points to the start of the string, p to a backslash, a control
     /// character, an ill-formed UTF-8 byte, or the end: decode the string into
     /// the arena
     NLOHMANN_VIEW_NOINLINE decoded slow_string(const unsigned char* s, const unsigned char* p)
     {
+        if (!enabled(Store))
+        {
+            // (accept(): the string is checked, not decoded)
+            static_cast<void>(s);
+            return check_string(p);
+        }
         // single-character escapes; 0: invalid (and 'u', handled separately)
         static const std::array<char, 128> simple_escape =
         {
@@ -343,6 +420,21 @@ class builder
                 }
                 arena_ensure(w, w_end, 4);
                 w = put_utf8(w, cp);
+                // A chain of unicode escapes ("\u3042\u3044\u3046", as Python's json.dumps writes non-ASCII text) is
+                // decoded here, without going round the loop above for each of them. Anything else (a surrogate, a
+                // bad digit, fewer than six bytes) leaves p at the backslash: the loop above handles it, and reports
+                // the same error at the same position as it would without this loop.
+                while (end - p >= 6 && p[0] == '\\' && p[1] == 'u')
+                {
+                    const int next = hex_codepoint(p + 2);
+                    if (next < 0 || (next & 0xF800) == 0xD800)
+                    {
+                        break;
+                    }
+                    p += 6;
+                    arena_ensure(w, w_end, 4);
+                    w = put_utf8(w, next);
+                }
             }
             else if (NLOHMANN_VIEW_LIKELY(d < 128 && simple_escape[d] != 0))
             {
@@ -610,10 +702,13 @@ run_found:
 
         NLOHMANN_VIEW_ALWAYS_INLINE bool run()
         {
-            cold.m_doc.reserve(estimate_nodes(reinterpret_cast<const char*>(b), static_cast<std::size_t>(e - b)));
+            if (enabled(Store))
-            base = cold.m_doc.nodes;
+            {
-            out = base;
+                cold.m_doc.reserve(estimate_nodes(reinterpret_cast<const char*>(b), static_cast<std::size_t>(e - b)));
-            cap = base + cold.m_doc.node_capacity;
+                base = cold.m_doc.nodes;
+                out = base;
+                cap = base + cold.m_doc.node_capacity;
+            }
 
             if (e - p >= 3 && p[0] == 0xEF && p[1] == 0xBB && p[2] == 0xBF)
             {
@@ -797,7 +892,10 @@ close_object:
             // an array pays nothing for this)
             if (NLOHMANN_VIEW_UNLIKELY(cur_count >= document_data::index_min_members))
             {
-                cold.note_large_object(cur_idx);
+                if (enabled(Store))
+                {
+                    cold.note_large_object(cur_idx);
+                }
             }
 
 close_container:
@@ -957,6 +1055,12 @@ indent_done:
         /// an integer's value); two stores on little-endian targets
         NLOHMANN_VIEW_ALWAYS_INLINE node* push_node(node_kind k, std::uint8_t flags, std::uint16_t extra, std::size_t off, std::uint64_t second)
         {
+            if (!enabled(Store))
+            {
+                // accept(): nothing is stored, so what computes the arguments is not run either. base and out stay
+                // null: their difference, which open() takes, is 0.
+                return out;
+            }
             if (NLOHMANN_VIEW_UNLIKELY(out == cap))
             {
                 const auto n = static_cast<std::size_t>(out - base);
@@ -1015,9 +1119,12 @@ indent_done:
 
         NLOHMANN_VIEW_ALWAYS_INLINE void close()
         {
-            node& n = base[cur_idx];
+            if (enabled(Store))
-            n.len = cur_count;
+            {
-            n.next = static_cast<std::uint32_t>(out - base) - cur_idx;
+                node& n = base[cur_idx];
+                n.len = cur_count;
+                n.next = static_cast<std::uint32_t>(out - base) - cur_idx;
+            }
             if (--depth != 0)
             {
                 if (NLOHMANN_VIEW_LIKELY(depth <= 64))
@@ -1082,7 +1189,7 @@ indent_done:
             {
                 ++p;
                 const unsigned char* const f0 = p;
-                p = skip_digits(p, e);
+                p = skip_fraction_digits(p, e);
                 if (NLOHMANN_VIEW_UNLIKELY(p == f0))
                 {
                     return fail(error_code::number_after_dot);
@@ -1192,34 +1299,44 @@ indent_done:
 };
 
 /// run the builder with compile-time options
-template<typename FloatType, bool Comments, bool TrailingCommas, bool NulIsEnd>
+template<typename FloatType, bool Comments, bool TrailingCommas, bool NulIsEnd, bool Store>
 inline bool build_with(document_data& d, const char* src, std::size_t size, bool sentinel, parse_failure& failure)
 {
     if (sentinel)
     {
-        builder<FloatType, Comments, TrailingCommas, NulIsEnd, true> bld(d, src, size);
+        builder<FloatType, Comments, TrailingCommas, NulIsEnd, true, Store> bld(d, src, size);
         const bool ok = bld.run();
         failure = bld.failure();
         return ok;
     }
-    builder<FloatType, Comments, TrailingCommas, NulIsEnd, false> bld(d, src, size);
+    builder<FloatType, Comments, TrailingCommas, NulIsEnd, false, Store> bld(d, src, size);
     const bool ok = bld.run();
     failure = bld.failure();
     return ok;
 }
 
 /// sentinel: src[size] is readable and 0 (e.g. std::string); FloatType: the
-/// number_float_t of the document
+/// number_float_t of the document; validate_only: accept(), only the result is
+/// used
 template<typename FloatType, bool NulIsEnd>
-inline bool build(document_data& d, const char* src, std::size_t size, bool comments, bool trailing_commas, bool sentinel, parse_failure& failure)
+inline bool build(document_data& d, const char* src, std::size_t size, bool comments, bool trailing_commas, bool sentinel, bool validate_only,
+                  parse_failure& failure)
 {
+    if (validate_only && !comments && !trailing_commas)
+    {
+        // accept() of plain JSON: nothing is stored. The other option sets
+        // could skip the stores just as well; they keep the builder that
+        // stores only so that there are two more instantiations of the parse
+        // loop, not eight.
+        return build_with<FloatType, false, false, NulIsEnd, false>(d, src, size, sentinel, failure);
+    }
     if (comments)
     {
-        return trailing_commas ? build_with<FloatType, true, true, NulIsEnd>(d, src, size, sentinel, failure)
+        return trailing_commas ? build_with<FloatType, true, true, NulIsEnd, true>(d, src, size, sentinel, failure)
-               : build_with<FloatType, true, false, NulIsEnd>(d, src, size, sentinel, failure);
+               : build_with<FloatType, true, false, NulIsEnd, true>(d, src, size, sentinel, failure);
     }
-    return trailing_commas ? build_with<FloatType, false, true, NulIsEnd>(d, src, size, sentinel, failure)
+    return trailing_commas ? build_with<FloatType, false, true, NulIsEnd, true>(d, src, size, sentinel, failure)
-           : build_with<FloatType, false, false, NulIsEnd>(d, src, size, sentinel, failure);
+           : build_with<FloatType, false, false, NulIsEnd, true>(d, src, size, sentinel, failure);
 }
 
 }  // namespace view

include/nlohmann/detail/view/edit.hpp

@@ -157,7 +157,7 @@ class editor
         node* const o = own(object);
         if (o->kind != node_kind::object && o->kind != node_kind::null)
         {
-            throw_type_error(exception_id::subscript_wrong_type, "cannot use operator[] with a string argument with ", object.type_name());
+            throw_type_error(site_of(object), exception_id::subscript_wrong_type, "cannot use operator[] with a string argument with ", object.type_name());
         }
         check_utf8(key.data(), key.size());
         const encoded e = encode(std::forward<V>(value));
@@ -208,9 +208,9 @@ class editor
         node* const a = own(array);
         if (a->kind != node_kind::array)
         {
-            throw_type_error(exception_id::subscript_wrong_type, "cannot use operator[] with a numeric argument with ", array.type_name());
+            throw_type_error(site_of(array), exception_id::subscript_wrong_type, "cannot use operator[] with a numeric argument with ", array.type_name());
         }
-        check_index(idx, a->len);
+        check_index(a, idx, a->len);
         const encoded e = encode(std::forward<V>(value));
         node* const slot = const_cast<node*>(nav::value(element_at<true>(m_doc, a, idx))); // NOLINT(cppcoreguidelines-pro-type-const-cast)
         assign(slot, e, a, true);
@@ -225,7 +225,7 @@ class editor
         node* const a = own(array);
         if (a->kind != node_kind::array && a->kind != node_kind::null)
         {
-            throw_type_error(exception_id::push_back_wrong_type, "cannot use push_back() with ", array.type_name());
+            throw_type_error(site_of(array), exception_id::push_back_wrong_type, "cannot use push_back() with ", array.type_name());
         }
         const encoded e = encode(std::forward<V>(value));
         if (a->kind == node_kind::null)
@@ -249,9 +249,9 @@ class editor
         node* const a = own(array);
         if (a->kind != node_kind::array)
         {
-            throw_type_error(exception_id::insert_wrong_type, "cannot use insert() with ", array.type_name());
+            throw_type_error(site_of(array), exception_id::insert_wrong_type, "cannot use insert() with ", array.type_name());
         }
-        check_index(idx, a->len + 1);
+        check_index(a, idx, a->len + 1);
         const encoded e = encode(std::forward<V>(value));
         node* const slot = new_slot(e);
         node* const h = block_of(m_doc, a, 1);
@@ -269,7 +269,7 @@ class editor
         node* const o = own(object);
         if (o->kind != node_kind::object)
         {
-            throw_type_error(exception_id::erase_wrong_type, "cannot use erase() with ", object.type_name());
+            throw_type_error(site_of(object), exception_id::erase_wrong_type, "cannot use erase() with ", object.type_name());
         }
         for (const node* k = nav::first(m_doc, o), *end = nav::end(m_doc, o); k != end; k = document_data::after(k + 1))
         {
@@ -287,9 +287,9 @@ class editor
         node* const a = own(array);
         if (a->kind != node_kind::array)
         {
-            throw_type_error(exception_id::erase_wrong_type, "cannot use erase() with ", array.type_name());
+            throw_type_error(site_of(array), exception_id::erase_wrong_type, "cannot use erase() with ", array.type_name());
         }
-        check_index(idx, a->len);
+        check_index(a, idx, a->len);
         node* const h = block_of(m_doc, a, 0);
         std::memmove(h + 1 + idx, h + 2 + idx, (h->next - 2 - idx) * sizeof(node));
         --h->next;
@@ -316,11 +316,11 @@ class editor
         return const_cast<node*>(v.m_node); // NOLINT(cppcoreguidelines-pro-type-const-cast): the nodes belong to this document
     }
 
-    static void check_index(std::size_t idx, std::size_t limit)
+    void check_index(const node* array, std::size_t idx, std::size_t limit) const
     {
         if (idx >= limit)
         {
-            throw_array_index_out_of_range(idx);
+            throw_array_index_out_of_range(error_site(&m_doc, array), idx);
         }
     }
 

include/nlohmann/detail/view/errors.hpp

@@ -10,11 +10,15 @@
 
 #include <algorithm> // min
 #include <cstddef> // size_t
-#include <string> // string
+#include <string> // string, to_string
+#include <vector> // vector
 
 #include <nlohmann/json.hpp>
 #include <nlohmann/detail/view/builder.hpp>
+#include <nlohmann/detail/view/document_data.hpp>
 #include <nlohmann/detail/view/macro_scope.hpp>
+#include <nlohmann/detail/view/materialize.hpp>
+#include <nlohmann/detail/view/node.hpp>
 
 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
@@ -22,8 +26,293 @@ namespace detail
 namespace view
 {
 
+/*!
+@brief the value an exception is about
+
+basic_json passes the value to the exception, which then names its path
+(JSON_DIAGNOSTICS) and its bytes in the source (JSON_DIAGNOSTIC_POSITIONS). A
+view's value has no parent pointer and no stored positions: both are found
+from the document and the node, when the exception is thrown (so only the
+error path pays for them). Without the two macros, a site is empty.
+*/
+class error_site
+{
+  public:
+    error_site() noexcept = default;
+
+#if JSON_DIAGNOSTICS || JSON_DIAGNOSTIC_POSITIONS
+    error_site(const document_data* d, const node* n) noexcept
+        : m_doc(d), m_node(n)
+    {}
+
+    const document_data* doc() const noexcept
+    {
+        return m_doc;
+    }
+    const node* value() const noexcept
+    {
+        return m_node;
+    }
+
+  private:
+    const document_data* m_doc = nullptr;
+    const node* m_node = nullptr;
+#else
+    error_site(const document_data* /*d*/, const node* /*n*/) noexcept {}
+#endif
+};
+
+/// the site of a view's value (the views make this a friend)
+struct view_access
+{
+    template<typename View>
+    static error_site site(const View& v) noexcept
+    {
+        return {v.m_doc, v.m_node};
+    }
+};
+
+template<typename View>
+error_site site_of(const View& v) noexcept
+{
+    static_assert(is_json_view<View>::value, "the site of a value is only defined for views");
+    return view_access::site(v);
+}
+
+#if JSON_DIAGNOSTICS
+/*!
+@brief the JSON pointer tokens from the root of document @a d to node @a target
+
+Nodes have no parent index, so the path is found by descending from the root:
+before the first edit, only into the subtree that contains the target (a
+container spans the next `next` nodes); after edits, elements can live in
+other sequences, so every container is searched. Iterative (the nesting depth
+is limited by memory only). False if the target is not found (then tokens is
+unspecified).
+*/
+template<bool Editable>
+bool value_path(const document_data& d, const node* target, std::vector<std::string>& tokens)
+{
+    using nav = navigation<Editable>;
+    struct frame
+    {
+        const node* pos;
+        const node* end;
+        std::size_t index;
+        bool object;
+    };
+    const node* const root = d.nodes;
+    if (target == root)
+    {
+        return true;
+    }
+    if (!is_container(*root))
+    {
+        return false;
+    }
+    std::vector<frame> stack;
+    stack.push_back(frame{nav::first(d, root), nav::end(d, root), 0, root->kind == node_kind::object});
+    // (tokens[i] leads from stack[i] to stack[i + 1], or to the target)
+    for (;;)
+    {
+        // a copy: pop_back() and push_back() below change the stack
+        const frame f = stack.back();
+        if (f.pos == f.end)
+        {
+            stack.pop_back();
+            if (stack.empty())
+            {
+                return false;
+            }
+            tokens.pop_back();
+            continue;
+        }
+        const node* entry = f.pos;
+        std::string token;
+        if (f.object)
+        {
+            // (as basic_json: the key up to a null byte)
+            token.assign(d.str(*entry), entry->len);
+            const std::size_t nul = token.find('\0');
+            if (nul != std::string::npos)
+            {
+                token.resize(nul);
+            }
+            ++entry;
+        }
+        else
+        {
+            token = std::to_string(f.index);
+        }
+        const node* const child = nav::value(entry);
+        if (child == target)
+        {
+            tokens.push_back(token);
+            return true;
+        }
+        stack.back().pos = document_data::after(entry);
+        ++stack.back().index;
+        if (is_container(*child) && (nav::editable() || (target > child && target < child + child->next)))
+        {
+            tokens.push_back(token);
+            stack.push_back(frame{nav::first(d, child), nav::end(d, child), 0, child->kind == node_kind::object});
+        }
+    }
+}
+#endif
+
+#if JSON_DIAGNOSTIC_POSITIONS
+/*!
+@brief the bytes [start, end) of node @a n in the source, as materialize() sets them
+
+Scalars as position_source::set_scalar; an array or object from its opening
+bracket to its closing bracket, which is found by following the chain of last
+elements to a scalar (or an empty container) and scanning from there to the
+closing brackets. None (npos) for values written by edits, and for containers
+whose last element has none, as with materialize().
+*/
+template<bool Editable>
+void value_range(const document_data& d, const node* n, std::size_t& start, std::size_t& end)
+{
+    using nav = navigation<Editable>;
+    position_source p;
+    start = std::string::npos;
+    end = std::string::npos;
+    if (!is_container(*n))
+    {
+        p.set_scalar(d, *n);
+        start = p.start;
+        end = p.end;
+        return;
+    }
+    if ((n->flags & node_flags::is_new) != 0 || n->off >= d.size)
+    {
+        return;
+    }
+    // the open brackets: n, then the last element as long as it is a non-empty container
+    std::size_t closing = 0;
+    std::size_t pos = std::string::npos;
+    for (const node* c = n;;)
+    {
+        if (!is_container(*c))
+        {
+            p.set_scalar(d, *c);
+            pos = p.end;
+            break;
+        }
+        if ((c->flags & node_flags::is_new) != 0 || c->off >= d.size)
+        {
+            return;
+        }
+        ++closing;
+        const node* const first = nav::first(d, c);
+        const node* const last_end = nav::end(d, c);
+        if (first == last_end)
+        {
+            pos = std::size_t{c->off} + 1;
+            break;
+        }
+        const std::size_t value_offset = c->kind == node_kind::object ? 1 : 0;
+        const node* last = first;
+        for (const node* e = document_data::after(first + value_offset); e != last_end; e = document_data::after(e + value_offset))
+        {
+            last = e;
+        }
+        c = nav::value(last + value_offset);
+    }
+    for (; closing != 0 && pos != std::string::npos; --closing)
+    {
+        pos = position_source::container_end(d.base[0], d.size, pos);
+    }
+    if (pos != std::string::npos)
+    {
+        start = n->off;
+        end = pos;
+    }
+}
+#endif
+
+/// the context basic_json puts in front of the message of an exception about
+/// a value: "(/path) " with JSON_DIAGNOSTICS (none for the root), then
+/// "(bytes a-b) " with JSON_DIAGNOSTIC_POSITIONS (with JSON_DIAGNOSTICS, only
+/// if there is a path)
+///
+/// This and the throw helpers that take an error_site are templates, so that
+/// the path and range code is instantiated only where an exception can be
+/// thrown: instantiated in every translation unit (as a non-template inline
+/// function makes it), it changed GCC's early inlining of unrelated view
+/// functions, so that GCC 13 no longer inlined a recursive walk over a view
+/// into itself (2.7 times the instructions).
+#if JSON_DIAGNOSTICS || JSON_DIAGNOSTIC_POSITIONS
+template<typename Unused = void>
+std::string diagnostics(const error_site site)
+{
+    if (site.doc() == nullptr || site.value() == nullptr)
+    {
+        return "";
+    }
+    const document_data& d = *site.doc();
+    const bool edited = d.edits != nullptr;
+    std::string context;
+#if JSON_DIAGNOSTICS
+    std::vector<std::string> tokens;
+    const bool found = edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens);
+    if (!found || tokens.empty())
+    {
+        // context is still empty; returning it keeps the copy elided (-Wnrvo)
+        return context;
+    }
+    std::string path;
+    for (const std::string& token : tokens)
+    {
+        path.push_back('/');
+        path += detail::escape(token);
+    }
+    context = concat('(', path, ") ");
+#endif
+#if JSON_DIAGNOSTIC_POSITIONS
+    std::size_t start = 0;
+    std::size_t end = 0;
+    if (edited)
+    {
+        value_range<true>(d, site.value(), start, end);
+    }
+    else
+    {
+        value_range<false>(d, site.value(), start, end);
+    }
+    if (start != std::string::npos && end != std::string::npos)
+    {
+        context += concat("(bytes ", std::to_string(start), "-", std::to_string(end), ") ");
+    }
+#endif
+    return context;
+}
+#else
+template<typename Unused = void>
+std::string diagnostics(const error_site /*site*/)
+{
+    return "";
+}
+#endif
+
+/// the context of an exception about view @a v (see exception_prefix())
+template<typename View>
+std::string diagnostics_of(const View& v)
+{
+    return diagnostics<>(site_of(v));
+}
+
 // Exceptions are thrown out of line, so that the accessors that may throw stay
-// small enough to be inlined.
+// small enough to be inlined. The overloads with an error_site put its context
+// in front of the message.
+//
+// The overloads without one are for exceptions that are not about a value of a
+// document: limits and invalid input of the editing and image functions, a
+// discarded view (it has no node), a view of another document (its path would
+// be one in that document), and those that basic_json creates without a
+// context too (the errors of json_pointer, invalid UTF-8). The one exception
+// about a value that has no site is key(), see view_iterator::key().
 
 [[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_type_error(exception_id id, const char* prefix, const char* type)
 {
@@ -45,6 +334,24 @@ namespace view
     NLOHMANN_VIEW_THROW(invalid_iterator::create(id, msg, nullptr));
 }
 
+template<typename Unused = void>
+[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_type_error(const error_site site, exception_id id, const char* prefix, const char* type)
+{
+    NLOHMANN_VIEW_THROW(type_error::create(id, concat(diagnostics<>(site), prefix, type), nullptr));
+}
+
+template<typename Unused = void>
+[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_out_of_range(const error_site site, exception_id id, const std::string& msg)
+{
+    NLOHMANN_VIEW_THROW(out_of_range::create(id, concat(diagnostics<>(site), msg), nullptr));
+}
+
+template<typename Unused = void>
+[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_invalid_iterator(const error_site site, exception_id id, const char* msg)
+{
+    NLOHMANN_VIEW_THROW(invalid_iterator::create(id, concat(diagnostics<>(site), msg), nullptr));
+}
+
 /// a parse error without a position (as those of json_pointer)
 [[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_parse_error(exception_id id, const std::string& msg)
 {
@@ -53,22 +360,23 @@ namespace view
 
 /// out_of_range.401: the array index @a idx is not below the size
 template<typename Index>
-[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_array_index_out_of_range(const Index idx)
+[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_array_index_out_of_range(const error_site site, const Index idx)
 {
-    throw_out_of_range(exception_id::array_index_out_of_range, concat("array index ", std::to_string(idx), " is out of range"));
+    throw_out_of_range(site, exception_id::array_index_out_of_range, concat("array index ", std::to_string(idx), " is out of range"));
 }
 
 /// out_of_range.402: the JSON Pointer token '-' of an array of @a size elements
-[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_array_index_past_end(std::size_t size)
+template<typename Unused = void>
+[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_array_index_past_end(const error_site site, std::size_t size)
 {
-    throw_out_of_range(exception_id::pointer_past_the_end_index, concat("array index '-' (", std::to_string(size), ") is out of range"));
+    throw_out_of_range(site, exception_id::pointer_past_the_end_index, concat("array index '-' (", std::to_string(size), ") is out of range"));
 }
 
 /// out_of_range.403: the object has no member @a key
 template<typename Key>
-[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_key_not_found(const Key& key)
+[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_key_not_found(const error_site site, const Key& key)
 {
-    throw_out_of_range(exception_id::key_not_found, concat("key '", key, "' not found"));
+    throw_out_of_range(site, exception_id::key_not_found, concat("key '", key, "' not found"));
 }
 
 /// SAX handler of the error replay: accepts every event without storing it,

include/nlohmann/detail/view/iterator.hpp

@@ -105,7 +105,10 @@ class view_iterator
     }
 
     /// the key of the current object member; throws invalid_iterator.207 for
-    /// other iterators, like basic_json's iterators
+    /// other iterators, like basic_json's iterators (but without the context
+    /// JSON_DIAGNOSTICS and JSON_DIAGNOSTIC_POSITIONS add: the iterator does not
+    /// know the value it iterates over, and keeping it would make iterators
+    /// larger, which keeps GCC from inlining recursive walks)
     string_view_t key() const
     {
         if (NLOHMANN_VIEW_UNLIKELY(m_value_offset == 0))

include/nlohmann/detail/view/macro_scope.hpp

@@ -40,6 +40,15 @@
     #define NLOHMANN_VIEW_NOINLINE
 #endif
 
+// GCC: a function compiled as written, without the clones in which interprocedural
+// constant propagation drops an argument that every caller passes as the same constant
+// (calling such a clone changes the code GCC generates for the parse loop that calls it)
+#if defined(__GNUC__) && !defined(__clang__)
+    #define NLOHMANN_VIEW_NOCLONE __attribute__((noclone))
+#else
+    #define NLOHMANN_VIEW_NOCLONE
+#endif
+
 #if defined(__GNUC__) || defined(__clang__)
     #define NLOHMANN_VIEW_NODISCARD __attribute__((warn_unused_result))
 #elif defined(_MSC_VER)

include/nlohmann/detail/view/macro_unscope.hpp

@@ -15,6 +15,7 @@
 #undef NLOHMANN_VIEW_UNLIKELY
 #undef NLOHMANN_VIEW_ALWAYS_INLINE
 #undef NLOHMANN_VIEW_NOINLINE
+#undef NLOHMANN_VIEW_NOCLONE
 #undef NLOHMANN_VIEW_NODISCARD
 #undef NLOHMANN_VIEW_THROW
 #undef NLOHMANN_VIEW_LITTLE_ENDIAN

include/nlohmann/detail/view/number.hpp

@@ -19,6 +19,7 @@
 #include <nlohmann/detail/view/macro_scope.hpp>
 #include <nlohmann/detail/view/node.hpp>
 #include <nlohmann/detail/view/scan.hpp>
+#include <nlohmann/detail/view/simd.hpp>
 
 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
@@ -103,12 +104,56 @@ NLOHMANN_VIEW_NOINLINE FloatType float_value(const char* first, const node& n)
     return convert_float<FloatType>(first, last, dot, mantissa_end);
 }
 
+#if NLOHMANN_VIEW_VECTOR
+/*!
+@brief the value of the first 16 digits of a run of digits with a point after
+int_digits of them (or none, if int_digits >= 16)
+
+The 17 bytes at p are read at once: the bytes after the point move down by one,
+then pairs, quadruples, and octets of digits are combined by multiplications
+(after simdjson). The bytes [p, p + 32) must be readable. Bytes that are not
+digits (only in a damaged image loaded with image_check::bounds) give a wrong
+value, but no undefined behavior.
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t sixteen_digits(const unsigned char* p, unsigned int_digits) noexcept
+{
+#if NLOHMANN_VIEW_NEON
+    const uint8x16_t low = vld1q_u8(p);
+    const uint8x16_t index = vcombine_u8(vcreate_u8(0x0706050403020100u), vcreate_u8(0x0F0E0D0C0B0A0908u));
+    const uint8x16_t before_point = vcltq_u8(index, vdupq_n_u8(static_cast<std::uint8_t>(int_digits)));
+    const uint8x16_t digits = vsubq_u8(vbslq_u8(before_point, low, vextq_u8(low, vld1q_u8(p + 16), 1)), vdupq_n_u8('0'));
+    const uint16x8_t twos = vpaddlq_u8(vmulq_u8(digits, vreinterpretq_u8_u16(vdupq_n_u16(0x010A))));
+    const uint32x4_t fours = vpaddlq_u16(vmulq_u16(twos, vreinterpretq_u16_u32(vdupq_n_u32(0x00010064))));
+    const uint64x2_t eights = vpaddlq_u32(vmulq_u32(fours, vreinterpretq_u32_u64(vdupq_n_u64(0x0000000100002710u))));
+    return (vgetq_lane_u64(eights, 0) * 100000000u) + vgetq_lane_u64(eights, 1);
+#else
+    // NOLINTBEGIN(portability-simd-intrinsics)
+    const __m128i low = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
+    const __m128i high = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p + 16))); // NOLINT(bugprone-casting-through-void)
+    const __m128i before_point = _mm_cmpgt_epi8(_mm_set1_epi8(static_cast<char>(int_digits)), _mm_setr_epi8(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15));
+    const __m128i moved = _mm_or_si128(_mm_srli_si128(low, 1), _mm_slli_si128(high, 15));
+    const __m128i digits = _mm_sub_epi8(_mm_or_si128(_mm_and_si128(before_point, low), _mm_andnot_si128(before_point, moved)), _mm_set1_epi8('0'));
+    // (16-bit lanes: SSE2 has no multiply-add of bytes)
+    const __m128i tens = _mm_setr_epi16(10, 1, 10, 1, 10, 1, 10, 1);
+    const __m128i twos = _mm_packs_epi32(_mm_madd_epi16(_mm_unpacklo_epi8(digits, _mm_setzero_si128()), tens),
+                                         _mm_madd_epi16(_mm_unpackhi_epi8(digits, _mm_setzero_si128()), tens));
+    const __m128i fours = _mm_madd_epi16(twos, _mm_setr_epi16(100, 1, 100, 1, 100, 1, 100, 1));
+    const __m128i eights = _mm_madd_epi16(_mm_packs_epi32(fours, fours), _mm_setr_epi16(10000, 1, 10000, 1, 10000, 1, 10000, 1));
+    const auto upper = static_cast<std::uint32_t>(_mm_cvtsi128_si32(eights));
+    const auto lower = static_cast<std::uint32_t>(_mm_cvtsi128_si32(_mm_srli_si128(eights, 4)));
+    // NOLINTEND(portability-simd-intrinsics)
+    return (std::uint64_t{upper} * 100000000u) + lower;
+#endif
+}
+#endif
+
 /*!
 @brief the digits of a float token with at most 19 digits, from its layout
 
 The digit layout recorded while parsing says where the integer digits, the
 fraction digits, and the exponent are, so the digits are read eight at a
-time without scanning.
+time without scanning (with SIMD, a token of 16 to 19 digits sixteen at a
+time).
 
 @param[in] p  first character of the token
 @param[in] e  end of the token
@@ -118,15 +163,34 @@ NLOHMANN_VIEW_ALWAYS_INLINE float_significand layout_decimal(const unsigned char
 {
     const bool negative = *p == '-';
     p += negative ? 1 : 0;
-    std::uint64_t w = parse_upto19(p, int_digits, limit);
+    std::uint64_t w = 0;
-    p += int_digits;
     std::int64_t q = 0;
-    if (frac_digits != 0)
+#if NLOHMANN_VIEW_VECTOR
+    const unsigned count = int_digits + frac_digits;
+    if (count >= 16 && limit - p >= 32)
     {
-        w = (w * int_pow10(frac_digits)) + parse_upto19(p + 1, frac_digits, limit);
+        // (the point, if any, follows the integer digits; the digits after
-        p += 1 + frac_digits;
+        // the first 16 are at most three)
+        w = sixteen_digits(p, int_digits);
+        for (unsigned i = 16; i < count; ++i)
+        {
+            w = (w * 10) + static_cast<std::uint64_t>(p[i + (i >= int_digits ? 1 : 0)] - '0');
+        }
+        p += count + (frac_digits != 0 ? 1 : 0);
         q = -static_cast<std::int64_t>(frac_digits);
     }
+    else /* NOLINT(readability/braces) */
+#endif
+    {
+        w = parse_upto19(p, int_digits, limit);
+        p += int_digits;
+        if (frac_digits != 0)
+        {
+            w = (w * int_pow10(frac_digits)) + parse_upto19(p + 1, frac_digits, limit);
+            p += 1 + frac_digits;
+            q = -static_cast<std::int64_t>(frac_digits);
+        }
+    }
     if (p != e)
     {
         // [eE][+-]digits; huge exponents saturate (the parser rejected
@@ -161,12 +225,22 @@ NLOHMANN_VIEW_ALWAYS_INLINE float_significand layout_decimal(const unsigned char
 The result is correctly rounded by the lexer's conversion
 (detail::decimal_to_float(): Clinger's fast path where both operands are
 exact, else the Eisel-Lemire algorithm, which needs no fallback for up to 19
-digits), so it is the value parse() produces.
+digits), so it is the value parse() produces. Tokens of 16 or more digits go
+to Eisel-Lemire directly: the fast path takes few of them (none of 17 digits),
+and its check is a branch that data like GeoJSON coordinates mispredicts.
 */
 template<typename FloatType>
 NLOHMANN_VIEW_ALWAYS_INLINE FloatType layout_float(const unsigned char* p, const unsigned char* e, unsigned int_digits, unsigned frac_digits, const unsigned char* limit) noexcept
 {
-    return decimal_to_float<FloatType>(layout_decimal(p, e, int_digits, frac_digits, limit));
+    const float_significand d = layout_decimal(p, e, int_digits, frac_digits, limit);
+    if (int_digits + frac_digits >= 16)
+    {
+        using format = ieee_binary_format<std::numeric_limits<FloatType>::digits>;
+        native_float_t<FloatType> value{};
+        float_from_bits(eisel_lemire<format>(d.exponent, d.w) | (d.negative ? (std::uint64_t{1} << format::sign_bit()) : 0u), value);
+        return value;
+    }
+    return decimal_to_float<FloatType>(d);
 }
 
 /// the value of a float set by an edit: its token (the shortest round-trip
@@ -185,6 +259,80 @@ NLOHMANN_VIEW_NOINLINE FloatType edited_float(const char* token, const node& n)
     return float_value<FloatType>(token, n);
 }
 
+#if NLOHMANN_VIEW_VECTOR
+/// eisel_lemire() for the token w * 10^q of coordinate_float()
+template<typename Format>
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t coordinate_bits(std::int64_t q, std::uint64_t w, Format /*format*/) noexcept
+{
+    return eisel_lemire<Format>(q, w);
+}
+
+/*!
+@brief (binary64) eisel_lemire() without the cases that tokens of 16 or 17
+digits with 5 or more after the point cannot reach: a value of 0, a
+subnormal, an infinity, or a tie (q < -4)
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t coordinate_bits(std::int64_t q, std::uint64_t w, ieee_binary_format<53> format) noexcept
+{
+    if (NLOHMANN_VIEW_UNLIKELY(w == 0 || q > -5))
+    {
+        return eisel_lemire<ieee_binary_format<53>>(q, w);
+    }
+    static_cast<void>(format);
+    const int lz = count_leading_zeros(w);
+    const std::uint64_t normalized = w << static_cast<unsigned>(lz);
+    const auto index = static_cast<std::size_t>(2 * (q - pow5_128_smallest_power));
+    const uint128_parts product = full_multiplication(normalized, pow5_128()[index]);
+    std::uint64_t high = product.high;
+    if (NLOHMANN_VIEW_UNLIKELY((high & 0x1FFu) == 0x1FFu))
+    {
+        // (the lower bits may carry into the result)
+        const std::uint64_t second = full_multiplication(normalized, pow5_128()[index + 1]).high;
+        high += product.low + second < product.low ? 1u : 0u;
+    }
+    const auto upperbit = static_cast<unsigned>(high >> 63u);
+    std::uint64_t mantissa = high >> (upperbit + 9);
+    auto power2 = static_cast<std::uint64_t>(((217706 * q) >> 16) + 63 + static_cast<std::int64_t>(upperbit) - lz + 1023);
+    mantissa = (mantissa + (mantissa & 1u)) >> 1u;
+    const bool carry = mantissa >= (std::uint64_t{2} << 52u);
+    mantissa = carry ? (std::uint64_t{1} << 52u) : mantissa;
+    power2 += carry ? 1u : 0u;
+    return (mantissa & ~(std::uint64_t{1} << 52u)) | (power2 << 52u);
+}
+
+/*!
+@brief (binary32 and binary64) the value of a float token of the source with
+16 or 17 digits, a point, and no exponent, the shape of most coordinates
+written with full precision; whether the token of n has this shape
+
+These tokens skip the general layout of layout_decimal(): no digits beyond
+the 17th, no exponent (and Eisel-Lemire directly, as in layout_float()).
+*/
+template<typename FloatType>
+NLOHMANN_VIEW_ALWAYS_INLINE bool coordinate_float(const document_data& d, const node& n, FloatType& value) noexcept
+{
+    const unsigned int_digits = n.extra & 0xFFu;
+    const unsigned frac_digits = n.extra >> 8u;
+    const unsigned count = int_digits + frac_digits;
+    const auto* const first = reinterpret_cast<const unsigned char*>(d.src + n.off); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    const unsigned negative = first[0] == '-' ? 1u : 0u;
+    if (count - 16u > 1u || frac_digits == 0 || n.len != negative + count + 1 || d.size - n.off < 33)
+    {
+        return false;
+    }
+    const unsigned char* const digits = first + negative;
+    const std::uint64_t w = sixteen_digits(digits, int_digits);
+    // (the 17th digit follows the point)
+    const std::uint64_t w17 = (w * 10) + static_cast<std::uint64_t>(digits[17] - '0');
+    using format = ieee_binary_format<std::numeric_limits<FloatType>::digits>;
+    native_float_t<FloatType> result{};
+    float_from_bits(coordinate_bits(-static_cast<std::int64_t>(frac_digits), count == 17 ? w17 : w, format{}) | (static_cast<std::uint64_t>(negative) << format::sign_bit()), result);
+    value = result;
+    return true;
+}
+
+#endif
+
 /// the value of the float token of a node, as parse() converts it; floats and
 /// doubles with at most 19 digits are converted from the digit layout
 template<typename FloatType>
@@ -200,6 +348,13 @@ FloatType float_value(const document_data& d, const node& n)
 template<typename FloatType>
 FloatType float_value(const document_data& d, const node& n, std::true_type /*binary32 or binary64*/)
 {
+#if NLOHMANN_VIEW_VECTOR
+    FloatType value {};
+    if (coordinate_float(d, n, value))
+    {
+        return value;
+    }
+#endif
     const unsigned int_digits = n.extra & 0xFFu;
     const unsigned frac_digits = n.extra >> 8u;
     if (NLOHMANN_VIEW_LIKELY(int_digits + frac_digits <= 19)) // (255 marks "many")

include/nlohmann/detail/view/pointer.hpp

@@ -44,6 +44,7 @@ index_status array_index(const StringType& s, std::size_t& idx) noexcept
 }
 
 /// throws the exception json_pointer::array_index throws for this status
+/// (without a context, as json_pointer::array_index)
 template<typename StringType>
 [[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_array_index_error(index_status status, const StringType& s)
 {
@@ -83,7 +84,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
             {
                 if (mode == pointer_mode::checked)
                 {
-                    throw_key_not_found(token);
+                    throw_key_not_found(site_of(cur), token);
                 }
                 return View();
             }
@@ -95,7 +96,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
             {
                 if (throwing)
                 {
-                    throw_array_index_past_end(cur.size());
+                    throw_array_index_past_end(site_of(cur), cur.size());
                 }
                 return View();
             }
@@ -114,7 +115,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
             {
                 if (mode == pointer_mode::checked)
                 {
-                    throw_array_index_out_of_range(idx);
+                    throw_array_index_out_of_range(site_of(cur), idx);
                 }
                 return View();
             }
@@ -124,7 +125,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
         {
             if (throwing)
             {
-                throw_out_of_range(exception_id::pointer_unresolved, concat("unresolved reference token '", token, "'"));
+                throw_out_of_range(site_of(cur), exception_id::pointer_unresolved, concat("unresolved reference token '", token, "'"));
             }
             return View();
         }

include/nlohmann/detail/view/scan.hpp

@@ -198,6 +198,57 @@ inline const unsigned char* find_block_comment_end(const unsigned char* p, const
     return p;
 }
 
+/// The digits of a fraction, whose number varies from one number to the next: skip_digits() with 16 bytes compared at
+/// once and the end of the run taken from a bit mask (SSE2), instead of a compare and a branch for each digit. That
+/// is about a third of the instructions for a fraction of 12 digits, and no branch that is mispredicted when the
+/// lengths vary. Where there is no SSE2, skip_digits() is used.
+#if NLOHMANN_VIEW_SSE2
+// The last bytes of the input, one at a time. GCC unrolls this loop in every inlined copy of the function below, which
+// makes the parse loop 4 KiB larger and slows down documents that have hardly any fractions; out of line, it does
+// not. Clang does better with the loop inline (a call in the parse loop costs it more than the unrolling).
+#if defined(__GNUC__) && !defined(__clang__)
+inline NLOHMANN_VIEW_NOINLINE const unsigned char* skip_digits_tail(const unsigned char* p, const unsigned char* e) noexcept
+{
+    while (p != e && is_digit(*p))
+    {
+        ++p;
+    }
+    return p;
+}
+#else
+NLOHMANN_VIEW_ALWAYS_INLINE const unsigned char* skip_digits_tail(const unsigned char* p, const unsigned char* e) noexcept
+{
+    while (p != e && is_digit(*p))
+    {
+        ++p;
+    }
+    return p;
+}
+#endif
+
+NLOHMANN_VIEW_ALWAYS_INLINE const unsigned char* skip_fraction_digits(const unsigned char* p, const unsigned char* e) noexcept
+{
+    while (e - p >= 16)
+    {
+        const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
+        // a digit is above '/' and below ':' (signed compares: a byte with the top bit set is negative, and neither)
+        const __m128i digits = _mm_and_si128(_mm_cmpgt_epi8(in, _mm_set1_epi8('/')), _mm_cmplt_epi8(in, _mm_set1_epi8(':')));
+        const auto not_digit = static_cast<std::uint64_t>(~static_cast<unsigned>(_mm_movemask_epi8(digits)) & 0xFFFFu);
+        if (not_digit != 0)
+        {
+            return p + count_trailing_zeros(not_digit);
+        }
+        p += 16;
+    }
+    return skip_digits_tail(p, e);
+}
+#else
+NLOHMANN_VIEW_ALWAYS_INLINE const unsigned char* skip_fraction_digits(const unsigned char* p, const unsigned char* e) noexcept
+{
+    return skip_digits(p, e);
+}
+#endif
+
 /// powers of ten up to 10^19 as integers
 inline std::uint64_t int_pow10(unsigned k) noexcept
 {

include/nlohmann/detail/view/serializer.hpp

@@ -14,7 +14,9 @@
 #include <cstddef> // size_t
 #include <cstdint> // uint8_t, uint32_t
 #include <cstring> // memcpy, memset
+#include <functional> // less
 #include <limits> // numeric_limits
+#include <memory> // unique_ptr
 #include <type_traits> // integral_constant
 #include <vector> // vector
 
@@ -384,6 +386,143 @@ struct depth_counter<false>
     }
 };
 
+/*!
+@brief where the double x nearest to a token w * 10^q lies, for 10^15 <= w <
+10^17 and -17 <= q <= -1 (Eisel-Lemire, then a fixed-point position)
+
+dump() writes the shortest decimal in the rounding interval of x (the closest
+one if there are several, see zmij::to_shortest()). Its digits are those of a
+multiple of 10^g of the token's last digit, with g = dec_exp + 1 - q for x's
+decimal exponent dec_exp: the multiple of 10^g nearest to x if it lies in the
+interval (at most one does), else the multiple of 10^(g - 1) nearest to x
+(see token_digits_1() and token_digits_2()). For g <= 0, the token itself is
+in the interval.
+
+The position is exact in a 64-bit fixed-point number with 56 bits after the
+point (of the token's last digit): x / 10^q = 2c * 5^-q / 2^t for x = c * 2^e2
+and t = q + 1 - e2, with at most 56 bits after the point here, and |x / 10^q -
+w| is at most half the spacing of the doubles, below 12 units. So only the low
+64 bits of 2c * 5^-q are needed. c and e2 come from Eisel-Lemire's product
+directly (as eisel_lemire() rounds it: no tie is possible for q < -4, and its
+second product is added where it can carry into the result).
+
+@param[out] offset  x / 10^q - w + 32, with 56 bits after the point
+@param[out] radius  half the spacing of the doubles at x, likewise (+ 1 if
+                    the interval is closed)
+@return g; 3 if the digits are not decided here (a power of two, whose
+        interval is not symmetric, or out of range)
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE int locate_token(std::uint64_t w, int q, std::uint64_t& offset, std::uint64_t& radius) noexcept
+{
+    const int lz = count_leading_zeros(w);
+    const std::uint64_t normalized = w << static_cast<unsigned>(lz);
+    const auto index = static_cast<std::size_t>(2 * (q - pow5_128_smallest_power));
+    const uint128_parts product = full_multiplication(normalized, pow5_128()[index]);
+    std::uint64_t high = product.high;
+    if (NLOHMANN_VIEW_UNLIKELY((high & 0x1FFu) == 0x1FFu))
+    {
+        // (as eisel_lemire(): the lower bits may carry into the result)
+        const std::uint64_t second = full_multiplication(normalized, pow5_128()[index + 1]).high;
+        high += product.low + second < product.low ? 1u : 0u;
+    }
+    const auto upperbit = static_cast<unsigned>(high >> 63u);
+    const std::uint64_t mantissa = high >> (upperbit + 9);
+    const std::uint64_t c = (mantissa + (mantissa & 1u)) >> 1u;
+    // e2 as eisel_lemire() computes the exponent (log2(10) ~ 217706 / 2^16)
+    const int e2 = static_cast<int>((217706 * static_cast<std::int64_t>(q)) >> 16) + 63 + static_cast<int>(upperbit) - lz - 52;
+    const int t = q + 1 - e2;
+    const int g = ((e2 * 315653) >> 20) + 1 - q; // (dec_exp as in zmij::to_shortest(), for a regular x)
+    static const std::array<std::uint64_t, 17> fives = {{1u, 5u, 25u, 125u, 625u, 3125u, 15625u, 78125u, 390625u, 1953125u, 9765625u, 48828125u, 244140625u, 1220703125u, 6103515625u, 30517578125u, 152587890625u}};
+    const std::uint64_t five = fives[static_cast<std::size_t>(-q)]; // 5^-q
+    const unsigned s = static_cast<unsigned>(56 - t) & 63u;
+    offset = ((2 * c * five) << s) - (w << 56u) + (std::uint64_t{32} << 56u);
+    radius = (five << s) + ((c & 1u) == 0 ? 1u : 0u);
+    // (c = 2^52: a power of two; c = 2^53: rounded up to one. With 8 to 16
+    // fraction digits, as the batch's tokens have, t is in [15, 40] and g at
+    // most 2. x lies halfway between two candidates only if its distance from
+    // the token is a whole unit (g == 2) or a half (g == 1): such tokens are
+    // left to the full conversion)
+    const bool decided = c - ((std::uint64_t{1} << 52u) + 1) < (std::uint64_t{1} << 52u) - 1
+                         && (offset & ((std::uint64_t{1} << 55u) - 1)) != 0;
+    return decided ? g : 3;
+}
+
+/// all bits set if b, else none
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t mask_if(bool b) noexcept
+{
+    return std::uint64_t{0} - static_cast<std::uint64_t>(b);
+}
+
+/// a if b, else c, without a branch (the conditions of token_digits_1/2() are
+/// as good as random, and GCC compiled their ?: as branches: one misprediction
+/// per float of canada.json on x86-64)
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t select_if(bool b, std::uint64_t a, std::uint64_t c) noexcept
+{
+    return c ^ ((a ^ c) & mask_if(b));
+}
+
+/// the distance of a position (see locate_token()) from the biased point 32
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t biased_distance(std::uint64_t position) noexcept
+{
+    constexpr std::uint64_t center = std::uint64_t{32} << 56u;
+    // |position - center|, without a branch: negated (complemented, plus 1) if below
+    const std::uint64_t below = mask_if(position < center);
+    return ((position - center) ^ below) - below;
+}
+
+/*!
+@brief (g == 1) the digits dump() writes for a token, from the position of its
+double (see locate_token()): the multiple of 10 nearest to x if it is in the
+interval, else w rounded to x (an exact tie between two candidates, like
+754570942.33984373, whose double is 754570942.33984375, is excluded by
+locate_token())
+
+With |x - w| at most the radius, which is below half the spacing of the
+candidates, the multiple of 10 nearest to x is w - r10 or the one above it.
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t token_digits_1(std::uint64_t w, std::uint64_t offset, std::uint64_t radius, std::uint64_t r10) noexcept
+{
+    constexpr std::uint64_t one = std::uint64_t{1} << 56u;
+    const std::uint64_t from = offset + (r10 * one); // x - (w - r10) (+ 32)
+    const bool up = from > 37 * one;                  // (nearer to the multiple above)
+    const bool shorter = biased_distance(from - (mask_if(up) & (10 * one))) < radius;
+    const std::uint64_t a = w - r10 + (mask_if(up) & 10u);
+    const std::uint64_t b = w + ((offset + (one / 2)) >> 56u) - 32;                // w rounded to x
+    return select_if(shorter, a, b);
+}
+
+/*!
+@brief (g == 2) the digits dump() writes for a token, as token_digits_1(): the
+multiple of 100 nearest to x if it is in the interval, else the multiple of 10
+nearest to x
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t token_digits_2(std::uint64_t w, std::uint64_t offset, std::uint64_t radius, std::uint64_t r10, std::uint64_t r100) noexcept
+{
+    constexpr std::uint64_t one = std::uint64_t{1} << 56u;
+    const std::uint64_t from = offset + (r100 * one);
+    const bool up = from > 82 * one;
+    const bool shorter = biased_distance(from - (mask_if(up) & (100 * one))) < radius;
+    const std::uint64_t a = w - r100 + (mask_if(up) & 100u);
+    // x - (w - r10), in [-12, 21]: the multiple of 10 nearest to x is that one,
+    // or one or two above, or one below
+    const std::uint64_t y = offset + (r10 * one);
+    const std::uint64_t steps = static_cast<std::uint64_t>(y > 37 * one) + static_cast<std::uint64_t>(y > 47 * one);
+    const bool down = y < 27 * one;
+    const std::uint64_t b = w - r10 + (10 * steps) - (mask_if(down) & 10u);
+    return select_if(shorter, a, b);
+}
+
+/// the four ASCII digits of x < 10^4, the first in the lowest byte (as
+/// little-endian memory holds them)
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint32_t four_digit_text(std::uint32_t x) noexcept
+{
+    const std::uint32_t ab = (x * 5243u) >> 19u; // x / 100
+    std::uint32_t v = ab | ((x - (ab * 100u)) << 16u);
+    const std::uint32_t a = ((v * 103u) >> 10u) & 0x000F000Fu; // / 10 per 16-bit lane
+    v = a | ((v - (a * 10u)) << 8u);
+    return v + 0x30303030u;
+}
+
 /// how the view's dump() writes a value
 struct dump_style
 {
@@ -711,6 +850,7 @@ class view_serializer
         std::array<frame, 32> buffer; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
         std::vector<frame> heap;
         small_stack<frame> stack(buffer.data(), buffer.size(), heap);
+        float_batch batch;
         const char* const src = m_doc.src;
         const char* const src_end = src + m_doc.size;
         char* w = m_out.cursor();
@@ -850,7 +990,7 @@ class view_serializer
                     else if (enabled(fast_double::value))
                     {
                         room(64);
-                        w = write_double_at(w, *n);
+                        w = write_double_ahead(w, src, n, batch);
                     }
                     else
                     {
@@ -875,6 +1015,20 @@ class view_serializer
                 case value_t::array:
                 {
                     const bool object = n->kind == node_kind::object;
+                    // (read-only documents, compact output) a pair of floats,
+                    // like the coordinates of GeoJSON, without a frame
+                    if (enabled(!Editable && !Pretty && !SourceNumbers && fast_double::value) && n->next == 3 && n->len == 2
+                            && n[1].kind == node_kind::number_float && n[2].kind == node_kind::number_float)
+                    {
+                        room(2 * 64);
+                        *w++ = '[';
+                        w = write_double_ahead(w, src, n + 1, batch);
+                        *w++ = ',';
+                        w = write_double_ahead(w, src, n + 2, batch);
+                        *w++ = ']';
+                        n += 2; // (the element before the next node)
+                        break;
+                    }
                     room(8);
                     if (n->len == 0)
                     {
@@ -984,6 +1138,254 @@ class view_serializer
         }
     }
 
+    /// (float_batch) the mark of digits whose rounding carried beyond the
+    /// token's last four (see mark())
+    static constexpr std::uint64_t carried() noexcept
+    {
+        return std::uint64_t{1} << 63u;
+    }
+
+    /// floats of 16 or 17 digits ahead of the walk, converted together (see
+    /// convert_ahead()), with their digits as mark() keeps them
+    struct float_batch
+    {
+        static constexpr std::size_t capacity() noexcept
+        {
+            return 256;
+        }
+        /// (on the heap, allocated by the first conversion: a frame of more
+        /// than a page made every dump of a small document slower)
+        struct entries
+        {
+            std::array<const node*, 256> at; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+            std::array<std::uint64_t, 256> digits; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        };
+        std::unique_ptr<entries> storage{};
+        const node** at = nullptr;
+        std::uint64_t* digits = nullptr;
+        std::size_t count = 0;
+        std::size_t next = 0;
+        const node* scanned = nullptr; ///< where the last scan of the node array ended
+    };
+
+    /// (doubles) the float at n as dump() writes it, at w (64 bytes of room):
+    /// from the batch if it holds n
+    NLOHMANN_VIEW_ALWAYS_INLINE char* write_double_ahead(char* w, const char* src, const node* n, float_batch& batch)
+    {
+#if NLOHMANN_VIEW_VECTOR && NLOHMANN_VIEW_LITTLE_ENDIAN
+        // (digits 0: not written by the batch; carried(): rounding carried
+        // beyond the last four digits)
+        if (batch.next != batch.count && batch.at[batch.next] == n && batch.digits[batch.next] - 1 < carried() - 1)
+        {
+            return write_token_digits(w, src, *n, batch.digits[batch.next++]);
+        }
+        return write_double_beside(w, n, batch);
+#else
+        static_cast<void>(src);
+        static_cast<void>(batch);
+        return write_double_at(w, *n);
+#endif
+    }
+
+#if NLOHMANN_VIEW_VECTOR && NLOHMANN_VIEW_LITTLE_ENDIAN
+    /// write_double_ahead() for a float that is not the batch's next one (out
+    /// of line: the walk is faster with less code in its loop)
+    NLOHMANN_VIEW_NOINLINE char* write_double_beside(char* w, const node* n, float_batch& batch)
+    {
+        // (an editable document's walk can skip nodes of the array)
+        const std::less<const node*> before{}; // NOLINT(modernize-use-transparent-functors) C++11 has no std::less<>
+        while (batch.next != batch.count && before(batch.at[batch.next], n))
+        {
+            ++batch.next;
+        }
+        if ((batch.next != batch.count && batch.at[batch.next] == n) || convert_ahead(n, batch))
+        {
+            const std::uint64_t digits = batch.digits[batch.next++];
+            if ((digits & carried()) != 0)
+            {
+                return write_carried_digits(w, *n, digits & ~carried());
+            }
+            if (digits != 0)
+            {
+                return write_token_digits(w, m_doc.src, *n, digits);
+            }
+        }
+        return write_double_at(w, *n);
+    }
+
+    /*!
+    @brief convert the floats of 16 or 17 digits among the next nodes of the
+    array at once; whether n is the first of them
+
+    Such tokens (like the coordinates of GeoJSON, written with 17 digits) are
+    written as the token with its last four digits replaced
+    (write_token_digits()). Each step (the digits, locate_token(),
+    token_digits_1/2()) is a long chain of dependent operations; one loop per
+    step over many floats lets the processor overlap the floats, which it does
+    not across the steps of one float (on Apple M1, one loop for the digits and
+    locate_token() made the dump of canada.json 12 % slower). Each node of the array
+    is scanned once; a node that the walk does not reach in order (in an
+    editable document) is written without the batch.
+    */
+    NLOHMANN_VIEW_NOINLINE bool convert_ahead(const node* n, float_batch& batch)
+    {
+        const std::less<const node*> before{}; // NOLINT(modernize-use-transparent-functors) C++11 has no std::less<>
+        const node* const last = m_doc.nodes + m_doc.node_count;
+        if (before(n, batch.scanned) || before(n, m_doc.nodes) || !before(n, last))
+        {
+            return false;
+        }
+        const char* const src = m_doc.src;
+        const char* const src_end = src + m_doc.size;
+        const node* const stop = last - n > 1024 ? n + 1024 : last;
+        batch.count = 0;
+        batch.next = 0;
+        // the digits of each token (and its last four from the text)
+        std::array<std::uint64_t, 256> digits;     // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<int, 256> exponent;             // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint32_t, 256> last_four;  // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        const node* p = n;
+        if (!batch.storage)
+        {
+            batch.storage.reset(new typename float_batch::entries); // NOLINT(cppcoreguidelines-owning-memory,modernize-make-unique): C++11
+            batch.at = batch.storage->at.data();
+            batch.digits = batch.storage->digits.data();
+        }
+        for (; p != stop && batch.count != float_batch::capacity(); ++p)
+        {
+            // a token of the source: 16 or 17 digits, at least 8 after the
+            // point, no exponent, 32 bytes to read
+            const unsigned frac_digits = p->extra >> 8u;
+            const unsigned int_digits = p->extra & 0xFFu;
+            const unsigned count = int_digits + frac_digits;
+            if (p->kind == node_kind::number_float && (p->flags & node_flags::storage) == 0
+                    && count - 16u <= 1u && frac_digits >= 8 && src_end - (src + p->off) >= 33)
+            {
+                const auto* const token = reinterpret_cast<const unsigned char*>(src + p->off); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+                const unsigned sign = token[0] == '-' ? 1 : 0;
+                const unsigned char* const first = token + sign;
+                const std::uint64_t w = sixteen_digits(first, int_digits);
+                // (the 17th digit follows the point; a token with an exponent
+                // gets digits outside the range of locate_token(), and is not
+                // written by the batch. A token 0.xxx with 16 significant
+                // digits is: its double is written as "0." and its digits too)
+                const std::uint64_t w17 = (w * 10) + static_cast<std::uint64_t>(first[17] - '0');
+                const std::size_t i = batch.count++;
+                batch.at[i] = p;
+                if (p->len != sign + count + 1)
+                {
+                    digits[i] = 0;
+                }
+                else
+                {
+                    digits[i] = count == 17 ? w17 : w;
+                }
+                exponent[i] = -static_cast<int>(frac_digits);
+                // (byte 0: the last digit, byte 1: the last two, bits 16-29: the last four)
+                std::uint32_t four = 0;
+                std::memcpy(&four, token + p->len - 4, 4);
+                four -= 0x30303030u;
+                const std::uint32_t pairs = ((four & 0x0F0F0F0Fu) * 2561u) >> 8u; // (byte 0, 2: the pairs)
+                last_four[i] = (four >> 24u) | ((pairs >> 16u & 0xFFu) << 8u) | ((((pairs & 0x00FF00FFu) * 6553601u) >> 16u) << 16u);
+            }
+        }
+        batch.scanned = p;
+        // the position of each double, and the floats of either kind
+        std::array<std::uint64_t, 256> offset; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint64_t, 256> radius; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint8_t, 256> kind_1;  // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint8_t, 256> kind_2;  // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::size_t count_1 = 0;
+        std::size_t count_2 = 0;
+        for (std::size_t i = 0; i != batch.count; ++i)
+        {
+            const std::uint64_t w = digits[i];
+            // (the range excludes the values of bytes that are not digits, only
+            // in a damaged image loaded with image_check::bounds)
+            const int g = w - 1000000000000000u < 99000000000000000u ? locate_token(w, exponent[i], offset[i], radius[i]) : 3;
+            batch.digits[i] = mask_if(g <= 0) & ((last_four[i] >> 16u) + 1);
+            kind_1[count_1] = static_cast<std::uint8_t>(i);
+            count_1 += static_cast<std::size_t>(g == 1);
+            kind_2[count_2] = static_cast<std::uint8_t>(i);
+            count_2 += static_cast<std::size_t>(g == 2);
+        }
+        // the digits to write, in one loop per kind (see mark())
+        for (std::size_t k = 0; k != count_1; ++k)
+        {
+            const std::size_t i = kind_1[k];
+            const std::uint64_t s = token_digits_1(digits[i], offset[i], radius[i], last_four[i] & 0xFFu);
+            batch.digits[i] = mark(digits[i], s, last_four[i] >> 16u);
+        }
+        for (std::size_t k = 0; k != count_2; ++k)
+        {
+            const std::size_t i = kind_2[k];
+            const std::uint64_t s = token_digits_2(digits[i], offset[i], radius[i], last_four[i] & 0xFFu, (last_four[i] >> 8u) & 0xFFu);
+            batch.digits[i] = mark(digits[i], s, last_four[i] >> 16u);
+        }
+        return batch.count != 0 && batch.at[0] == n;
+    }
+
+    /*!
+    @brief a float token of 16 or 17 digits as dump() writes it, at w (64 bytes
+    of room), from the digits of its double (see locate_token()) whose
+    rounding carried beyond the token's last four digits
+
+    (like 43.42027299999999 -> 43.420273): the digits go to the writer of
+    Zmij's results as its 15 or 16 leading digits and one more, which omits
+    the trailing zeros.
+    */
+    NLOHMANN_VIEW_NOINLINE char* write_carried_digits(char* w, const node& n, std::uint64_t digits) const noexcept
+    {
+        const int exponent = -(n.extra >> 8u);
+        const std::uint64_t leading = digits / 10;
+        const auto last = static_cast<unsigned char>(digits - (leading * 10));
+        const bool seventeen = digits >= 10000000000000000u;
+        *w = '-';
+        w += m_doc.src[n.off] == '-' ? 1 : 0;
+        return ::nlohmann::detail::dtoa_impl::write_shortest(w, seventeen ? ::nlohmann::detail::zmij::shortest_decimal{leading, exponent, last, last != 0}
+                : ::nlohmann::detail::zmij::shortest_decimal{digits, exponent - 1, 0, false});
+    }
+
+    /// the digits s of a token with the digits w and the last four digits
+    /// r4, as the batch keeps them: the new last four digits + 1 (only those
+    /// are written over the token's), or s marked if it differs from w beyond
+    /// them (0 stays for a float the batch does not write)
+    static std::uint64_t mark(std::uint64_t w, std::uint64_t s, std::uint64_t r4) noexcept
+    {
+        const std::uint64_t last = s - (w - r4);
+        return last < 10000 ? last + 1 : s | carried();
+    }
+
+    /*!
+    @brief a float token of 16 or 17 digits as dump() writes it, at w (64 bytes
+    of room): the token with its last four digits replaced by digits - 1 (see
+    mark(); the others are the token's), and without trailing zeros after the
+    point, but one
+    */
+    char* write_token_digits(char* w, const char* src, const node& n, std::uint64_t digits)
+    {
+        const char* const token = src + n.off;
+        std::memcpy(w, token, 32);
+        char* const end = w + n.len;
+        const std::uint32_t last = four_digit_text(static_cast<std::uint32_t>(digits - 1));
+        std::memcpy(end - 4, &last, 4);
+        // (the token's text before the new digits, from the source: reading
+        // the output back would wait for the stores)
+        std::uint64_t before = 0;
+        std::memcpy(&before, token + n.len - 12, 8);
+        const std::uint32_t last_zeros = last ^ 0x30303030u;
+        const std::uint64_t before_zeros = before ^ 0x3030303030303030u;
+        if (NLOHMANN_VIEW_UNLIKELY(last_zeros == 0 && before_zeros == 0))
+        {
+            return write_double_at(w, n); // (twelve or more trailing zeros)
+        }
+        const unsigned zeros = last_zeros != 0 ? (static_cast<unsigned>(count_leading_zeros(last_zeros)) / 8) - 4
+                               : 4 + (static_cast<unsigned>(count_leading_zeros(before_zeros)) / 8);
+        const unsigned frac_digits = n.extra >> 8u;
+        return end - (zeros < frac_digits ? zeros : frac_digits - 1);
+    }
+#endif
+
     /// a float node as dump() writes it
     void write_float_node(const node& n)
     {

include/nlohmann/detail/view/simd.hpp

@@ -289,9 +289,12 @@ compares, and the UTF-8 check covers the bytes up to it. Returns where the
 string scan stops, like scan_string_run: before ill-formed UTF-8 and for the
 last bytes of the input, the bytes are checked one sequence at a time. Out of
 line, so that no constants of the check occupy registers in the parse loop.
-On x86-64, it is compiled for SSSE3 (see cpu_has_ssse3()).
+On x86-64, it is compiled for SSSE3 (see cpu_has_ssse3()). Not cloned: with
+the calls of accept()'s builder, GCC 16 would clone it without plain (always
+string_plain()), and calling the clone made json_document::parse() run 0.7-1.2 %
+more instructions.
 */
-NLOHMANN_VIEW_SSSE3_TARGET NLOHMANN_VIEW_NOINLINE inline const unsigned char* scan_string_vector(const unsigned char* p, const unsigned char* e, const std::uint8_t* plain) noexcept
+NLOHMANN_VIEW_SSSE3_TARGET NLOHMANN_VIEW_NOINLINE NLOHMANN_VIEW_NOCLONE inline const unsigned char* scan_string_vector(const unsigned char* p, const unsigned char* e, const std::uint8_t* plain) noexcept
 {
     using lookup = utf8_lookup4<>;
     const unsigned char* block = p;

include/nlohmann/detail/view/value.hpp

@@ -33,12 +33,37 @@ namespace view
 template<typename T>
 struct value_tag {};
 
+/// whether basic_json reads T with a dedicated from_json() overload that does
+/// not accept a boolean: exactly number_integer_t, number_unsigned_t and
+/// number_float_t (the other arithmetic types convert a boolean to 0 or 1)
+template<typename T, typename BasicJsonType>
+struct rejects_boolean : std::integral_constant < bool,
+    std::is_same<T, typename BasicJsonType::number_integer_t>::value
+    || std::is_same<T, typename BasicJsonType::number_unsigned_t>::value
+    || std::is_same<T, typename BasicJsonType::number_float_t>::value >
+{};
+
+/// a boolean as T: 0 or 1
+template<typename T>
+NLOHMANN_VIEW_ALWAYS_INLINE T boolean_as(const document_data& /*d*/, const node& n, std::false_type /*rejects*/)
+{
+    return static_cast<T>((n.flags & node_flags::is_true) != 0);
+}
+
+/// a boolean as number_integer_t, number_unsigned_t or number_float_t: type_error.302, as in basic_json
+template<typename T>
+[[noreturn]] NLOHMANN_VIEW_ALWAYS_INLINE T boolean_as(const document_data& d, const node& n, std::true_type /*rejects*/)
+{
+    throw_type_error(error_site(&d, &n), exception_id::type_mismatch, "type must be number, but is ", value_type_name(static_cast<value_t>(n.kind)));
+}
+
 /*!
 @brief the number or boolean of a node converted to an arithmetic type
 
 As basic_json's get<T>() for arithmetic types: integers and floats are
-converted with static_cast, booleans give 0 or 1, and other types throw
+converted with static_cast, booleans give 0 or 1 (but throw type_error.302 for
-type_error.302.
+number_integer_t, number_unsigned_t and number_float_t, as basic_json does),
+and other types throw type_error.302.
 */
 template<typename T, typename BasicJsonType>
 NLOHMANN_VIEW_ALWAYS_INLINE T arithmetic_value(const document_data& d, const node& n)
@@ -52,7 +77,7 @@ NLOHMANN_VIEW_ALWAYS_INLINE T arithmetic_value(const document_data& d, const nod
         case value_t::number_float:
             return static_cast<T>(float_value<typename BasicJsonType::number_float_t>(d, n));
         case value_t::boolean:
-            return static_cast<T>((n.flags & node_flags::is_true) != 0);
+            return boolean_as<T>(d, n, rejects_boolean<T, BasicJsonType> {});
         case value_t::null:
         case value_t::object:
         case value_t::array:
@@ -60,7 +85,7 @@ NLOHMANN_VIEW_ALWAYS_INLINE T arithmetic_value(const document_data& d, const nod
         case value_t::binary:
         case value_t::discarded:
         default:
-            throw_type_error(exception_id::type_mismatch, "type must be number, but is ", value_type_name(static_cast<value_t>(n.kind)));
+            throw_type_error(error_site(&d, &n), exception_id::type_mismatch, "type must be number, but is ", value_type_name(static_cast<value_t>(n.kind)));
     }
 }
 
@@ -70,7 +95,7 @@ std::vector<U, A> vector_value(const View& v)
 {
     if (NLOHMANN_VIEW_UNLIKELY(!v.is_array()))
     {
-        throw_type_error(exception_id::type_mismatch, "type must be array, but is ", v.type_name());
+        throw_type_error(site_of(v), exception_id::type_mismatch, "type must be array, but is ", v.type_name());
     }
     std::vector<U, A> r;
     r.reserve(v.size());
@@ -88,7 +113,7 @@ Map map_value(const View& v)
 {
     if (NLOHMANN_VIEW_UNLIKELY(!v.is_object()))
     {
-        throw_type_error(exception_id::type_mismatch, "type must be object, but is ", v.type_name());
+        throw_type_error(site_of(v), exception_id::type_mismatch, "type must be object, but is ", v.type_name());
     }
     Map r;
     for (auto it = v.begin(); it != v.end(); ++it)

include/nlohmann/json.hpp

@@ -150,7 +150,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     // can be restored when json_pointer backwards compatibility is removed
     // friend ::nlohmann::json_pointer<StringType>;
 
-    template<typename BasicJsonType, typename InputType>
+    template<typename BasicJsonType, typename InputType, bool DiscardValues>
     friend class ::nlohmann::detail::parser;
     friend ::nlohmann::detail::serializer<basic_json>;
     template<typename BasicJsonType>
@@ -183,12 +183,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         detail::parser_callback_t<basic_json>cb = nullptr,
         const bool allow_exceptions = true,
         const bool ignore_comments = false,
-        const bool ignore_trailing_commas = false,
+        const bool ignore_trailing_commas = false
-        const bool discard_number_values = false
     )
     {
         return ::nlohmann::detail::parser<basic_json, InputAdapterType>(std::move(adapter),
-               std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas, discard_number_values);
+               std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
     }
 
   private:
@@ -3117,7 +3116,9 @@ public:
                             const bool ignore_comments,
                             const bool ignore_trailing_commas)
     {
-        return parser(std::forward<InputAdapterType>(adapter), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
+        // the parser and lexer that discard the values of tokens (see lexer)
+        return ::nlohmann::detail::parser<basic_json, typename std::decay<InputAdapterType>::type, true>(std::forward<InputAdapterType>(adapter),
+                nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
     /// generate SAX events from the input behind an already created adapter

include/nlohmann/json_view.hpp

@@ -285,7 +285,7 @@ class basic_json_view
             {
                 return {};
             }
-            detail::view::throw_type_error(detail::exception_id::subscript_wrong_type, "cannot use operator[] with a string argument with ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::subscript_wrong_type, "cannot use operator[] with a string argument with ", type_name());
         }
         return lookup(key);
     }
@@ -311,7 +311,7 @@ class basic_json_view
             {
                 return {};
             }
-            detail::view::throw_type_error(detail::exception_id::subscript_wrong_type, "cannot use operator[] with a numeric argument with ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::subscript_wrong_type, "cannot use operator[] with a numeric argument with ", type_name());
         }
         return idx < m_node->len ? element(idx) : basic_json_view();
     }
@@ -344,12 +344,12 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_object()))
         {
-            detail::view::throw_type_error(detail::exception_id::at_wrong_type, "cannot use at() with ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::at_wrong_type, "cannot use at() with ", type_name());
         }
         const basic_json_view r = lookup(key);
         if (NLOHMANN_VIEW_UNLIKELY(r.is_discarded()))
         {
-            detail::view::throw_key_not_found(std::string(key.data(), key.size()));
+            detail::view::throw_key_not_found(site(), std::string(key.data(), key.size()));
         }
         return r;
     }
@@ -370,11 +370,11 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_array()))
         {
-            detail::view::throw_type_error(detail::exception_id::at_wrong_type, "cannot use at() with ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::at_wrong_type, "cannot use at() with ", type_name());
         }
         if (NLOHMANN_VIEW_UNLIKELY(idx >= m_node->len))
         {
-            detail::view::throw_array_index_out_of_range(idx);
+            detail::view::throw_array_index_out_of_range(site(), idx);
         }
         return element(idx);
     }
@@ -402,7 +402,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_object()))
         {
-            detail::view::throw_type_error(detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
         }
         const basic_json_view r = lookup(key);
         return r.is_discarded() ? default_value : r.template get<T>();
@@ -412,7 +412,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_object()))
         {
-            detail::view::throw_type_error(detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
         }
         // (the default is made only if there is no such member)
         const basic_json_view r = lookup(key);
@@ -427,7 +427,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_structured()))
         {
-            detail::view::throw_type_error(detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
         }
         const basic_json_view r = detail::view::resolve_pointer(*this, detail::json_pointer_access::reference_tokens(ptr), detail::view::pointer_mode::value);
         return r.is_discarded() ? default_value : r.template get<T>();
@@ -437,7 +437,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_structured()))
         {
-            detail::view::throw_type_error(detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
         }
         const basic_json_view r = detail::view::resolve_pointer(*this, detail::json_pointer_access::reference_tokens(ptr), detail::view::pointer_mode::value);
         return r.is_discarded() ? string_t(default_value) : r.template get<string_t>();
@@ -450,7 +450,7 @@ class basic_json_view
         const iterator it = begin();
         if (NLOHMANN_VIEW_UNLIKELY(it == end()))
         {
-            detail::view::throw_invalid_iterator(detail::exception_id::iterator_value_unavailable, "cannot get value");
+            detail::view::throw_invalid_iterator(site(), detail::exception_id::iterator_value_unavailable, "cannot get value");
         }
         return *it;
     }
@@ -606,7 +606,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_string()))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be string, but is ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::type_mismatch, "type must be string, but is ", type_name());
         }
         return {m_doc->str(*m_node), m_node->len};
     }
@@ -618,7 +618,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_number()))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be number, but is ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::type_mismatch, "type must be number, but is ", type_name());
         }
         return {m_doc->str(*m_node), detail::view::number_length(*m_node)};
     }
@@ -764,15 +764,19 @@ class basic_json_view
     template<typename, view_mode> friend class basic_json_view;
     template<typename, typename> friend class detail::view::editor;
     template<typename, typename> friend class detail::view::view_side;
+    friend struct detail::view::view_access;
     friend iterator;
 
-    /// whether the view is one of an editable document
-    static constexpr bool is_editable = Editable;
-
     basic_json_view(const document_data* d, const node* n) noexcept
         : m_doc(d), m_node(n)
     {}
 
+    /// this value as the context of an exception
+    detail::view::error_site site() const noexcept
+    {
+        return {m_doc, m_node};
+    }
+
     using json_side_t = detail::view::json_side<BasicJsonType, string_view_t>;
 
     static detail::view::view_side<BasicJsonType, basic_json_view> side(const basic_json_view& v) noexcept
@@ -879,7 +883,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_boolean()))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be boolean, but is ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::type_mismatch, "type must be boolean, but is ", type_name());
         }
         return (m_node->flags & detail::view::node_flags::is_true) != 0;
     }
@@ -889,7 +893,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(m_node == nullptr))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be number, but is ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::type_mismatch, "type must be number, but is ", type_name());
         }
         return detail::view::arithmetic_value<T, BasicJsonType>(*m_doc, *m_node);
     }
@@ -898,7 +902,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_null()))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be null, but is ", type_name());
+            detail::view::throw_type_error(site(), detail::exception_id::type_mismatch, "type must be null, but is ", type_name());
         }
         return nullptr;
     }
@@ -1063,7 +1067,7 @@ class basic_json_document
                                      const bool ignore_trailing_commas = false)
     {
         basic_json_document d;
-        d.read_range(first, last, allow_exceptions, ignore_comments, ignore_trailing_commas);
+        d.read_range(first, last, error_mode(allow_exceptions), ignore_comments, ignore_trailing_commas);
         return d;
     }
 
@@ -1078,7 +1082,7 @@ class basic_json_document
         basic_json_document d;
         std::string buf;
         append_input(buf, std::forward<InputType>(input));
-        d.build_owned(std::move(buf), allow_exceptions, ignore_comments, ignore_trailing_commas);
+        d.build_owned(std::move(buf), error_mode(allow_exceptions), ignore_comments, ignore_trailing_commas);
         return d;
     }
 
@@ -1091,7 +1095,8 @@ class basic_json_document
     static bool accept(InputType&& input, const bool ignore_comments = false, const bool ignore_trailing_commas = false)
     {
         basic_json_document d;
-        d.read(std::forward<InputType>(input), false, ignore_comments, ignore_trailing_commas);
+        d.read_kind(std::forward<InputType>(input), on_error::validate, ignore_comments, ignore_trailing_commas,
+                    std::integral_constant<detail::view::input_kind, detail::view::classify_input<InputType>::value> {});
         return !d.is_discarded();
     }
 
@@ -1107,7 +1112,7 @@ class basic_json_document
               const bool ignore_comments = false,
               const bool ignore_trailing_commas = false)
     {
-        read_kind(std::forward<InputType>(input), allow_exceptions, ignore_comments, ignore_trailing_commas,
+        read_kind(std::forward<InputType>(input), error_mode(allow_exceptions), ignore_comments, ignore_trailing_commas,
                   std::integral_constant<detail::view::input_kind, detail::view::classify_input<InputType>::value> {});
     }
 
@@ -1312,7 +1317,7 @@ class basic_json_document
     template<typename I, typename V, typename std::enable_if<detail::view::is_non_bool_integral<I>::value, int>::type = 0>
     view_type set(view_type array, I idx, V && value)
     {
-        return editor().set(array, index(idx), std::forward<V>(value));
+        return editor().set(array, index(array, idx), std::forward<V>(value));
     }
 
     /// set the value at a JSON pointer: its parent must exist; an object
@@ -1349,7 +1354,7 @@ class basic_json_document
                 const std::size_t idx = pointer_index(token);
                 if (idx >= 0xFFFFFFFFu)
                 {
-                    detail::view::throw_array_index_out_of_range(idx);
+                    detail::view::throw_array_index_out_of_range(detail::view::site_of(parent), idx);
                 }
                 for (std::size_t i = 0; i < idx; ++i)
                 {
@@ -1383,7 +1388,7 @@ class basic_json_document
     template<typename I, typename V, typename std::enable_if<detail::view::is_non_bool_integral<I>::value, int>::type = 0>
     view_type insert(view_type array, I idx, V && value)
     {
-        return editor().insert(array, index(idx), std::forward<V>(value));
+        return editor().insert(array, index(array, idx), std::forward<V>(value));
     }
 
     /// remove all members with this key; returns their number
@@ -1396,7 +1401,7 @@ class basic_json_document
     template<typename I, typename std::enable_if<detail::view::is_non_bool_integral<I>::value, int>::type = 0>
     void erase(view_type array, I idx)
     {
-        editor().erase(array, index(idx));
+        editor().erase(array, index(array, idx));
     }
 
     /// remove the value at a JSON pointer; returns the number of removed
@@ -1430,25 +1435,25 @@ class basic_json_document
         return detail::view::editor<BasicJsonType, view_type>(*m_data);
     }
 
-    /// an index (out_of_range.401 if negative)
+    /// an index into @a array (out_of_range.401 if negative)
     template<typename I>
-    static std::size_t index(I idx)
+    static std::size_t index(const view_type& array, I idx)
     {
-        return index(idx, std::is_signed<I> {});
+        return index(array, idx, std::is_signed<I> {});
     }
 
     template<typename I>
-    static std::size_t index(I idx, std::true_type /*signed*/)
+    static std::size_t index(const view_type& array, I idx, std::true_type /*signed*/)
     {
         if (idx < 0)
         {
-            detail::view::throw_array_index_out_of_range(idx);
+            detail::view::throw_array_index_out_of_range(detail::view::site_of(array), idx);
         }
         return static_cast<std::size_t>(idx);
     }
 
     template<typename I>
-    static std::size_t index(I idx, std::false_type /*unsigned*/)
+    static std::size_t index(const view_type& /*array*/, I idx, std::false_type /*unsigned*/)
     {
         return static_cast<std::size_t>(idx);
     }
@@ -1466,6 +1471,22 @@ class basic_json_document
         return idx;
     }
 
+    /// what a failed parse does
+    enum class on_error : std::uint8_t
+    {
+        discard, ///< the document is discarded
+        raise,   ///< parse_error is thrown
+        validate ///< accept(): the document is discarded, and no node is stored while parsing
+    };
+
+    static on_error error_mode(bool allow_exceptions) noexcept
+    {
+        return allow_exceptions ? on_error::raise : on_error::discard;
+    }
+
+    /// NulIsEnd of the builder: a null byte ends the input unless strict_nul_handling
+    static constexpr bool nul_is_end = !detail::abi_config::strict_nul_handling;
+
     /// create the storage (sized for the input) on first use
     void ensure_data(const char* src, std::size_t size)
     {
@@ -1477,7 +1498,7 @@ class basic_json_document
 
     /// parse a buffer the document takes ownership of (it replaces the
     /// previous owned copy)
-    void build_owned(std::string&& buf, bool allow_exceptions, bool comments, bool trailing_commas)
+    void build_owned(std::string&& buf, on_error allow_exceptions, bool comments, bool trailing_commas)
     {
         ensure_data(buf.data(), buf.size());
         m_data->owned = std::move(buf);
@@ -1487,7 +1508,7 @@ class basic_json_document
     /// parse a copy of the input; the copy is appended to the cleared owned
     /// buffer, so that its capacity is reused
     template<typename T>
-    void build_copy(T&& input, bool allow_exceptions, bool comments, bool trailing_commas)
+    void build_copy(T&& input, on_error allow_exceptions, bool comments, bool trailing_commas)
     {
         if (!m_data)
         {
@@ -1508,7 +1529,7 @@ class basic_json_document
     }
 
     /// sentinel: src[size] is readable and 0 (std::string, C strings)
-    void build(const char* src, std::size_t size, bool allow_exceptions, bool comments, bool trailing_commas, bool owned, bool sentinel)
+    void build(const char* src, std::size_t size, on_error allow_exceptions, bool comments, bool trailing_commas, bool owned, bool sentinel)
     {
         ensure_data(src, size);
         document_data& d = *m_data;
@@ -1535,7 +1556,8 @@ class basic_json_document
         }
         else
         {
-            ok = detail::view::build < typename BasicJsonType::number_float_t, !detail::abi_config::strict_nul_handling > (d, src, size, comments, trailing_commas, sentinel, failure);
+            ok = detail::view::build<typename BasicJsonType::number_float_t, nul_is_end>(d, src, size, comments, trailing_commas, sentinel,
+                 allow_exceptions == on_error::validate, failure);
         }
         if (NLOHMANN_VIEW_LIKELY(ok))
         {
@@ -1548,7 +1570,7 @@ class basic_json_document
             return;
         }
         std::vector<std::uint32_t>().swap(d.large_objects);
-        if (allow_exceptions)
+        if (allow_exceptions == on_error::raise)
         {
             detail::view::throw_parse_failure<BasicJsonType>(failure, src, size, comments, trailing_commas);
         }
@@ -1556,13 +1578,13 @@ class basic_json_document
 
     // --- input dispatch (see detail::view::input_kind) ---
 
-    void read_kind(std::string&& s, bool ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::move_string> /*unused*/)
+    void read_kind(std::string&& s, on_error ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::move_string> /*unused*/)
     {
         build_owned(std::move(s), ae, c, tc);
     }
 
     template<typename CharT>
-    void read_kind(CharT* s, bool ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::c_string> /*unused*/)
+    void read_kind(CharT* s, on_error ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::c_string> /*unused*/)
     {
         if (s == nullptr)
         {
@@ -1576,7 +1598,7 @@ class basic_json_document
     }
 
     template<typename Array>
-    void read_kind(Array& a, bool ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::char_array> /*unused*/)
+    void read_kind(Array& a, on_error ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::char_array> /*unused*/)
     {
         using CharT = typename std::remove_cv<typename std::remove_extent<Array>::type>::type;
         const std::size_t n = std::extent<Array>::value;
@@ -1587,7 +1609,7 @@ class basic_json_document
     }
 
     template<typename T>
-    void read_kind(const T& s, bool ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::borrow_range> /*unused*/)
+    void read_kind(const T& s, on_error ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::borrow_range> /*unused*/)
     {
         // std::basic_string guarantees data()[size()] == 0: use it as sentinel
         const auto size = static_cast<std::size_t>(s.size());
@@ -1596,13 +1618,13 @@ class basic_json_document
     }
 
     template<typename T>
-    void read_kind(const T& s, bool ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::copy_range> /*unused*/)
+    void read_kind(const T& s, on_error ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::copy_range> /*unused*/)
     {
         build_copy(s, ae, c, tc);
     }
 
     template<typename CharT>
-    void read_kind(CharT* s, bool ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::wide_c_string> /*unused*/)
+    void read_kind(CharT* s, on_error ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::wide_c_string> /*unused*/)
     {
         if (s == nullptr)
         {
@@ -1614,13 +1636,13 @@ class basic_json_document
     }
 
     template<typename T>
-    void read_kind(T&& input, bool ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::adapter> /*unused*/)
+    void read_kind(T&& input, on_error ae, bool c, bool tc, std::integral_constant<input_kind, input_kind::adapter> /*unused*/)
     {
         build_copy(std::forward<T>(input), ae, c, tc);
     }
 
     template<typename IteratorType>
-    void read_range(IteratorType first, IteratorType last, bool ae, bool c, bool tc)
+    void read_range(IteratorType first, IteratorType last, on_error ae, bool c, bool tc)
     {
         using value_type = typename std::remove_cv<typename std::iterator_traits<IteratorType>::value_type>::type;
         // borrow the range where the library's input adapter scans it as one
@@ -1631,14 +1653,14 @@ class basic_json_document
     }
 
     template<typename IteratorType>
-    void read_range_impl(IteratorType first, IteratorType last, bool ae, bool c, bool tc, std::true_type /*contiguous bytes*/)
+    void read_range_impl(IteratorType first, IteratorType last, on_error ae, bool c, bool tc, std::true_type /*contiguous bytes*/)
     {
         const auto size = static_cast<std::size_t>(std::distance(first, last));
         build(size == 0 ? "" : reinterpret_cast<const char*>(&*first), size, ae, c, tc, false, size == 0); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
     }
 
     template<typename IteratorType>
-    void read_range_impl(IteratorType first, IteratorType last, bool ae, bool c, bool tc, std::false_type /*other*/)
+    void read_range_impl(IteratorType first, IteratorType last, on_error ae, bool c, bool tc, std::false_type /*other*/)
     {
         build_copy(detail::view::make_adapter_input(detail::input_adapter(first, last)), ae, c, tc);
     }

tests/src/json_view_test_helpers.hpp

@@ -15,6 +15,7 @@
 #include <nlohmann/json_view.hpp>
 
 #include <algorithm> // any_of
+#include <cstddef> // size_t
 #include <functional> // function
 #include <random> // mt19937
 #include <string> // string
@@ -88,6 +89,27 @@ inline bool has_duplicate_keys(const nlohmann::ordered_json_view& v)
     });
 }
 
+// the message of an exception about the value at path (a JSON pointer, "" for
+// the root) whose source bytes are [start, end): the context basic_json adds
+// with JSON_DIAGNOSTICS and JSON_DIAGNOSTIC_POSITIONS, if enabled, then what
+inline std::string message(const std::string& id, const std::string& path, std::size_t start, std::size_t end, const std::string& what)
+{
+#if JSON_DIAGNOSTIC_POSITIONS
+    const std::string positions = "(bytes " + std::to_string(start) + "-" + std::to_string(end) + ") ";
+#else
+    const std::string positions;
+    static_cast<void>(start);
+    static_cast<void>(end);
+#endif
+#if JSON_DIAGNOSTICS
+    const std::string context = path.empty() ? "" : "(" + path + ") " + positions;
+#else
+    const std::string& context = positions;
+    static_cast<void>(path);
+#endif
+    return "[json.exception." + id + "] " + context + what;
+}
+
 #if !defined(JSON_NOEXCEPTION)
 // the exception a call throws, or "" if it throws none
 inline std::string exception_of_call(const std::function<void()>& f)

tests/src/unit-bjdata.cpp

@@ -26,11 +26,14 @@ using nlohmann::ordered_json;
 #include <limits>
 #include <iostream>
 #include <fstream>
+#include <list>
 #include <set>
 #include "make_test_data_available.hpp"
 #include "test_utils.hpp"
 #include "sax_countdown.hpp"
+#include "sax_event_loggers.hpp"
 using utils::SaxCountdown;
+using utils::SaxEventLogger;
 
 
 // trait_test_arg and the "value_in_range_of trait" TEST_CASE_TEMPLATE_DEFINE
@@ -4746,3 +4749,77 @@ TEST_CASE("BJData optimized container type marker is validated for count 0")
         CHECK(json::from_bjdata(vb) == json::binary({}));
     }
 }
+
+TEST_CASE("BJData optimized arrays from contiguous and non-contiguous input")
+{
+    // contiguous input reads the numbers of an array with a type marker in
+    // one loop, other input number by number; both must give the same events,
+    // value, or error for the complete document and for every truncation of
+    // it, and stop at every event a SAX handler rejects
+    json document =
+    {
+        {"u8", {0, 200, 255}},
+        {"i8", {-5, 100, -128}},
+        {"i16", {-30000, 1000, 30000}},
+        {"i32", {-2000000000, 5, 70000}},
+        {"i64", {-9000000000000000000LL, 1, 5000000000LL}},
+        {"f64", {1.5, -0.1, 2.5}},
+        {"pairs", {{1.25, -3.75}, {1.25, -3.75}, json::array()}},
+        {"mixed", {1, "a", 2.5, nullptr}},
+        {"u16", {40000, 1, 65535}},
+        {"u32", {4000000000U, 1, 70000}},
+        {"u64", {18446744073709551615ULL, 1, 5000000000ULL}},
+        {"nd", {{"_ArrayType_", "double"}, {"_ArraySize_", {2, 2}}, {"_ArrayData_", {1.5, -2.5, 3.5, -4.5}}}},
+        {"nd8", {{"_ArrayType_", "uint8"}, {"_ArraySize_", {3}}, {"_ArrayData_", {1, 2, 3}}}},
+    };
+    const std::vector<std::uint8_t> encoded = json::to_bjdata(document, true, true);
+    CHECK(json::from_bjdata(encoded) == document);
+
+    for (std::size_t length = 0; length <= encoded.size(); ++length)
+    {
+        CAPTURE(length)
+        const std::vector<std::uint8_t> contiguous(encoded.begin(), encoded.begin() + static_cast<std::ptrdiff_t>(length));
+        const std::list<std::uint8_t> bytewise(contiguous.begin(), contiguous.end());
+
+        CHECK(json::from_bjdata(contiguous, true, false).dump() == json::from_bjdata(bytewise.begin(), bytewise.end(), true, false).dump());
+#if !defined(JSON_NOEXCEPTION)
+        std::string contiguous_error;
+        std::string bytewise_error;
+        try
+        {
+            json _;
+            _ = json::from_bjdata(contiguous);
+        }
+        catch (const json::exception& e)
+        {
+            contiguous_error = e.what();
+        }
+        try
+        {
+            json _;
+            _ = json::from_bjdata(bytewise.begin(), bytewise.end());
+        }
+        catch (const json::exception& e)
+        {
+            bytewise_error = e.what();
+        }
+        CHECK(contiguous_error == bytewise_error);
+#endif
+
+        SaxEventLogger from_contiguous;
+        SaxEventLogger from_bytewise;
+        CHECK(json::sax_parse(contiguous, &from_contiguous, json::input_format_t::bjdata)
+              == json::sax_parse(bytewise.begin(), bytewise.end(), &from_bytewise, json::input_format_t::bjdata));
+        CHECK(from_contiguous.events == from_bytewise.events);
+    }
+
+    for (int events = 0; events <= 80; ++events)
+    {
+        CAPTURE(events)
+        const std::list<std::uint8_t> bytewise(encoded.begin(), encoded.end());
+        SaxCountdown from_contiguous(events);
+        SaxCountdown from_bytewise(events);
+        CHECK(json::sax_parse(encoded, &from_contiguous, json::input_format_t::bjdata)
+              == json::sax_parse(bytewise.begin(), bytewise.end(), &from_bytewise, json::input_format_t::bjdata));
+    }
+}

tests/src/unit-bson.cpp

@@ -19,6 +19,7 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
+#include <array>
 #include <cstdint>
 #include <fstream>
 #include <limits>
@@ -1164,7 +1165,13 @@ TEST_CASE("BSON keys from contiguous and stream input")
     // contiguous input reads a key up to its \x00-byte in one step, a stream
     // reads it byte by byte; both must give the same value or error for the
     // complete document and for every truncation of it
-    const json j = {{"", true}, {"k", {1, 2, 3}}, {std::string(40, 'x'), {{"nested key", "value"}}}};
+    json j = {{"", true}, {"k", {1, 2, 3}}, {std::string(40, 'x'), {{"nested key", "value"}}}};
+    // keys and array element names ("0" to "11") that end at every position of
+    // an 8-byte word, which contiguous input scans at a time
+    for (std::size_t length = 1; length <= 17; ++length)
+    {
+        j[std::string(length, static_cast<char>('a' + length))] = json::array({0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, {11}});
+    }
     const std::vector<std::uint8_t> bson = json::to_bson(j);
     CHECK(json::from_bson(bson) == j);
 
@@ -1184,7 +1191,7 @@ TEST_CASE("BSON keys from contiguous and stream input")
         }
         try
         {
-            std::istringstream stream(std::string(input.begin(), input.end()));
+            std::istringstream stream(std::string(reinterpret_cast<const char*>(input.data()), input.size()));
             from_stream = json::from_bson(stream).dump();
         }
         catch (const json::parse_error& e)
@@ -1194,6 +1201,33 @@ TEST_CASE("BSON keys from contiguous and stream input")
         CHECK(from_vector == from_stream);
     }
 }
+
+TEST_CASE("BSON array element names")
+{
+    // an array's element names are not part of the value, so they are not
+    // passed on; error_handler_t::strict still rejects ill-formed UTF-8 in them
+    const std::vector<std::uint8_t> bson =
+    {
+        0x1D, 0x00, 0x00, 0x00, // size (little endian)
+        0x04, 'a', 0x00,        // entry: array "a"
+        0x15, 0x00, 0x00, 0x00, // size (little endian)
+        0x08, 0xFF, 0x00, 0x01, // entry: boolean named "\xFF", true
+        0x08, '1', '2', '3', '4', '5', '6', '7', '8', '9', 0x00, 0x00, // entry: boolean named "123456789", false
+        0x00,                   // end of the array
+        0x00                    // end of the document
+    };
+    const json expected = {{"a", {true, false}}};
+
+    CHECK(json::from_bson(bson) == expected);
+    CHECK(json::from_bson(bson, true, true, json::error_handler_t::replace) == expected);
+    CHECK(json::from_bson(bson, true, true, json::error_handler_t::ignore) == expected);
+
+    json _;
+    CHECK_THROWS_WITH_AS(_ = json::from_bson(bson, true, true, json::error_handler_t::strict), "[json.exception.parse_error.113] parse error at byte 14: syntax error while parsing BSON key: invalid string: ill-formed UTF-8 byte", json::parse_error&);
+
+    std::istringstream stream(std::string(reinterpret_cast<const char*>(bson.data()), bson.size()));
+    CHECK(json::from_bson(stream) == expected);
+}
 #endif
 
 TEST_CASE("Negative size of binary value")
@@ -2267,3 +2301,153 @@ TEST_CASE("BSON large strings and binaries (chunked reader)")
         }
     }
 }
+
+TEST_CASE("BSON written in one pass and in two passes")
+{
+    // to_bson() into a returned vector writes each size once the object or
+    // array is complete; through an output adapter, all sizes are computed
+    // first. Both must produce the same bytes and throw the same exceptions.
+    const auto two_pass = [](const json & j, const json::error_handler_t handler)
+    {
+        std::vector<std::uint8_t> result;
+        json::to_bson(j, result, handler);
+        return result;
+    };
+
+    const auto check_same = [&](const json & j, const json::error_handler_t handler)
+    {
+        CAPTURE(j.dump(-1, ' ', true, json::error_handler_t::replace))
+        CAPTURE(static_cast<int>(handler))
+#if !defined(JSON_NOEXCEPTION)
+        std::string one_pass_error;
+        std::string two_pass_error;
+        std::vector<std::uint8_t> one;
+        std::vector<std::uint8_t> two;
+        try
+        {
+            one = json::to_bson(j, handler);
+        }
+        catch (const json::exception& e)
+        {
+            one_pass_error = e.what();
+        }
+        try
+        {
+            two = two_pass(j, handler);
+        }
+        catch (const json::exception& e)
+        {
+            two_pass_error = e.what();
+        }
+        CHECK(one_pass_error == two_pass_error);
+        CHECK(one == two);
+#else
+        CHECK(json::to_bson(j, handler) == two_pass(j, handler));
+#endif
+    };
+
+    const std::array<json::error_handler_t, 4> handlers = {{
+            json::error_handler_t::keep, json::error_handler_t::strict,
+            json::error_handler_t::replace, json::error_handler_t::ignore
+        }
+    };
+
+    SECTION("corpus")
+    {
+        for (const auto& value : utils::round_trip_corpus::values())
+        {
+            const json document = value.is_object() ? value : json{{"value", value}};
+            for (const auto handler : handlers)
+            {
+                check_same(document, handler);
+            }
+        }
+    }
+
+    SECTION("nesting and arrays of every length class")
+    {
+        json document = json::object();
+        document["empty object"] = json::object();
+        document["empty array"] = json::array();
+        for (const std::size_t n :
+                {
+                    1u, 9u, 10u, 11u, 99u, 100u, 101u, 1000u
+                })
+        {
+            json numbers = json::array();
+            json mixed = json::array();
+            for (std::size_t i = 0; i < n; ++i)
+            {
+                numbers.push_back(i % 3 == 0 ? json(static_cast<double>(i) / 3) : json(static_cast<std::int64_t>(i) * 1000003));
+                switch (i % 4)
+                {
+                    case 0:
+                        mixed.push_back(json("s" + std::to_string(i)));
+                        break;
+                    case 1:
+                        mixed.push_back(json::array({i, json::object({{"k", i}})}));
+                        break;
+                    case 2:
+                        mixed.push_back(json(nullptr));
+                        break;
+                    default:
+                        mixed.push_back(json(i % 2 == 0));
+                        break;
+                }
+            }
+            document["numbers " + std::to_string(n)] = numbers;
+            document["mixed " + std::to_string(n)] = mixed;
+            document["nested " + std::to_string(n)] = json::object({{"a", numbers}, {"b", json::array({mixed, json::object()})}});
+        }
+        document["binary"] = json::binary({1, 2, 3}, 0x80);
+        document["binary old"] = json::binary({1, 2, 3}, 0x02);
+        for (const auto handler : handlers)
+        {
+            check_same(document, handler);
+        }
+    }
+
+#if !defined(JSON_NOEXCEPTION)
+    // every entry here throws, which aborts without exceptions
+    SECTION("errors at every position")
+    {
+        // an entry that cannot be written, at each place among valid ones
+        const std::string bad_utf8 = "\xC3\x28";
+        const std::array<json, 7> bad_entries =
+        {
+            {
+                json::object({{std::string("a\0b", 3), 1}}),
+                json::object({{"s", bad_utf8}}),
+                json::object({{bad_utf8, 1}}),
+                json::array({1, 2, bad_utf8}),
+                json::object({{"b", json::binary({1}, 0x100)}}),
+                json::object({{"d", json(json::value_t::discarded)}}),
+                json::array({json(json::value_t::discarded)}),
+            }
+        };
+        for (const auto& bad : bad_entries)
+        {
+            for (std::size_t pos = 0; pos < 4; ++pos)
+            {
+                json document = json::object();
+                json list = json::array();
+                for (std::size_t i = 0; i < 4; ++i)
+                {
+                    if (i == pos)
+                    {
+                        document["x" + std::to_string(i)] = bad;
+                        list.push_back(bad);
+                    }
+                    document["n" + std::to_string(i)] = json::array({i, "str", json::object({{"k", i}})});
+                    list.push_back(i);
+                }
+                document["list"] = list;
+                for (const auto handler : handlers)
+                {
+                    check_same(document, handler);
+                }
+            }
+        }
+    }
+#endif
+}

tests/src/unit-cbor.cpp

@@ -29,7 +29,9 @@ using nlohmann::json;
 #include "round_trip_corpus.hpp"
 #include "test_utils.hpp"
 #include "sax_countdown.hpp"
+#include "sax_event_loggers.hpp"
 using utils::SaxCountdown;
+using utils::SaxEventLogger;
 
 
 TEST_CASE("CBOR")
@@ -2446,6 +2448,78 @@ TEST_CASE("CBOR SAX parsing stops at every event")
     CHECK(count_events(std::vector<std::uint8_t>({0xBF, 0x61, 'a', 0x9F, 0x01, 0xFF, 0xFF})) == 6);
 }
 
+TEST_CASE("CBOR arrays of scalars from contiguous and non-contiguous input")
+{
+    // contiguous input reads the integers, floats, booleans, and nulls an
+    // array begins with in one loop, other input value by value; both must
+    // give the same events, value, or error for the complete document and for
+    // every truncation of it, and stop at every event a SAX handler rejects
+    const std::vector<std::uint8_t> cbor =
+    {
+        0xA3,                                                       // map(3)
+        0x61, 'a',                                                  // "a"
+        0x98, 0x16,                                                 // array(22)
+        0x00, 0x17, 0x18, 0xFF, 0x19, 0x01, 0x00,                   // 0, 23, 255, 256
+        0x1A, 0x00, 0x01, 0x00, 0x00,                               // 65536
+        0x1B, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,       // 18446744073709551615
+        0x20, 0x37, 0x38, 0xFF, 0x39, 0x01, 0x00,                   // -1, -24, -256, -257
+        0x3A, 0x00, 0x01, 0x00, 0x00,                               // -65537
+        0x3B, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,       // -18446744073709551616 (a float)
+        0x3B, 0x7F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,       // -9223372036854775808
+        0xF4, 0xF5, 0xF6,                                           // false, true, null
+        0xFA, 0x3F, 0xC0, 0x00, 0x00,                               // 1.5 (float32)
+        0xFB, 0xBF, 0xB9, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9A,       // -0.1
+        0xF9, 0x3C, 0x00,                                           // 1.0 (float16, ends the loop)
+        0x01, 0x61, 'a',                                            // 1, "a"
+        0xFB, 0x40, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,       // 2.5
+        0x61, 'b',                                                  // "b"
+        0x83,                                                       // array(3)
+        0x82, 0xFB, 0x3F, 0xF4, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // [1.25,
+        0xFB, 0xC0, 0x0E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,       //  -3.75]
+        0x82, 0xFB, 0x3F, 0xF4, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // [1.25,
+        0xFB, 0xC0, 0x0E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,       //  -3.75]
+        0x80,                                                       // []
+        0x61, 'c',                                                  // "c"
+        0x84, 0xA0, 0x01, 0xC1, 0x02, 0x81, 0x03                    // [{}, 1, tag(1) 2, [3]]
+    };
+    const auto tags = json::cbor_tag_handler_t::ignore;
+
+    const json j = json::from_cbor(cbor, true, true, tags);
+    CHECK(j["a"].size() == 22);
+    CHECK(j["a"][5] == 18446744073709551615u);
+    CHECK(j["a"][11].is_number_float());
+    CHECK(j["a"][11] == -18446744073709551616.0);
+    CHECK(j["a"][12] == (std::numeric_limits<std::int64_t>::min)());
+    CHECK(j["a"][17] == -0.1);
+    CHECK(j["b"] == json::parse("[[1.25, -3.75], [1.25, -3.75], []]"));
+    CHECK(j["c"] == json::parse("[{}, 1, 2, [3]]"));
+
+    for (std::size_t length = 0; length <= cbor.size(); ++length)
+    {
+        CAPTURE(length)
+        const std::vector<std::uint8_t> contiguous(cbor.begin(), cbor.begin() + static_cast<std::ptrdiff_t>(length));
+        const std::list<std::uint8_t> bytewise(contiguous.begin(), contiguous.end());
+
+        CHECK(json::from_cbor(contiguous, true, false, tags).dump() == json::from_cbor(bytewise.begin(), bytewise.end(), true, false, tags).dump());
+
+        SaxEventLogger from_contiguous;
+        SaxEventLogger from_bytewise;
+        CHECK(json::sax_parse(contiguous, &from_contiguous, json::input_format_t::cbor, true, false, false, tags)
+              == json::sax_parse(bytewise.begin(), bytewise.end(), &from_bytewise, json::input_format_t::cbor, true, false, false, tags));
+        CHECK(from_contiguous.events == from_bytewise.events);
+    }
+
+    for (int events = 0; events <= 60; ++events)
+    {
+        CAPTURE(events)
+        const std::list<std::uint8_t> bytewise(cbor.begin(), cbor.end());
+        SaxCountdown from_contiguous(events);
+        SaxCountdown from_bytewise(events);
+        CHECK(json::sax_parse(cbor, &from_contiguous, json::input_format_t::cbor, true, false, false, tags)
+              == json::sax_parse(bytewise.begin(), bytewise.end(), &from_bytewise, json::input_format_t::cbor, true, false, false, tags));
+    }
+}
+
 TEST_CASE("CBOR indefinite-length strings do not recurse per chunk")
 {
     // Reading an indefinite-length string or byte array used to call itself

tests/src/unit-class_parser.cpp

@@ -2982,6 +2982,67 @@ TEST_CASE("accept() agrees with parse() on floats around the overflow limit")
     }
 }
 
+TEST_CASE("accept() agrees with parse() on strings, which it checks without copying them")
+{
+    // accept() scans strings and object keys with a separate instantiation of
+    // the string scanner that does not copy them into the token buffer; it
+    // must accept and reject exactly what parse() does
+    const std::vector<std::string> pieces =
+    {
+        "", "abc", R"(\"\\\/\b\f\n\r\t)", R"(\u0041\u00e4\u20AC)", "\\ud83d\\ude00", "\\uD83D\\uDE00",
+        "\\ud800", "\\udc00", "\\ud800\\u0041", "\\ud800x", "\\udbff\\udfff", "\\u12", "\\u12g4", "\\x", "\\",
+        "\xc3\xa4", "\xe2\x82\xac", "\xf0\x9f\x98\x80", "\xf4\x8f\xbf\xbf", "\xc0\xaf", "\xed\xa0\x80", "\xf4\x90\x80\x80",
+        "\xff", "\xe2\x82", "\xc3", "\x01", "\x1f", "\x7f", "\n", std::string(1, '\0')
+    };
+
+    for (std::size_t run = 0; run <= 70; ++run)
+    {
+        for (const std::string& piece : pieces)
+        {
+            // a run of ordinary characters puts the piece at every offset of the bulk scanners
+            const std::string str = std::string(run, 'a') + piece;
+            std::string opened = "\"";
+            opened += str;
+            std::string closed = opened;
+            closed += '"';
+            std::vector<std::string> texts;
+            texts.push_back(closed);
+            texts.emplace_back("[");
+            texts.back() += closed;
+            texts.back() += ']';
+            texts.emplace_back("{");
+            texts.back() += closed;
+            texts.back() += ":1}";
+            texts.emplace_back("{\"k\":");
+            texts.back() += closed;
+            texts.back() += ',';
+            texts.back() += closed;
+            texts.back() += ":[";
+            texts.back() += closed;
+            texts.back() += "]}";
+            texts.emplace_back("[");
+            texts.back() += opened;
+            for (const std::string& text : texts)
+            {
+                CAPTURE(text)
+                for (int options = 0; options < 4; ++options)
+                {
+                    const bool ignore_comments = (options & 1) != 0;
+                    const bool ignore_trailing_commas = (options & 2) != 0;
+                    const bool parses = !json::parse(text, nullptr, false, ignore_comments, ignore_trailing_commas).is_discarded();
+                    CHECK(json::accept(text, ignore_comments, ignore_trailing_commas) == parses);
+
+                    std::istringstream stream(text);
+                    CHECK(json::accept(stream, ignore_comments, ignore_trailing_commas) == parses);
+
+                    const std::list<char> chars(text.begin(), text.end());
+                    CHECK(json::accept(chars.begin(), chars.end(), ignore_comments, ignore_trailing_commas) == parses);
+                }
+            }
+        }
+    }
+}
+
 namespace
 {
 // a DOM parser that reports parse errors without throwing, as in the sax_no_exception example

tests/src/unit-conversions1.cpp

@@ -1260,6 +1260,44 @@ TEST_CASE("value conversion")
     #undef JSON_HAS_CPP_17
 #endif
 
+TEST_CASE("get<T>() of a boolean (#5988)")
+{
+    // a boolean converts to 0/1 for every arithmetic type except number_integer_t, number_unsigned_t and
+    // number_float_t, whose dedicated from_json() overloads throw
+    const json t = true;
+    const json f = false;
+
+    SECTION("0 and 1")
+    {
+        // long and unsigned long are left out: they are std::int64_t and std::uint64_t on some platforms
+        CHECK(t.get<bool>() == true);
+        CHECK(f.get<bool>() == false);
+        CHECK(t.get<char>() == 1);
+        CHECK(t.get<signed char>() == 1);
+        CHECK(t.get<unsigned char>() == 1);
+        CHECK(t.get<short>() == 1); // NOLINT(google-runtime-int)
+        CHECK(t.get<unsigned short>() == 1); // NOLINT(google-runtime-int)
+        CHECK(t.get<int>() == 1);
+        CHECK(t.get<unsigned>() == 1);
+        CHECK(t.get<float>() == 1.0F);
+        CHECK(t.get<long double>() == 1.0L);
+        CHECK(f.get<int>() == 0);
+        CHECK(f.get<float>() == 0.0F);
+    }
+
+#if !defined(JSON_NOEXCEPTION)
+    SECTION("number_integer_t, number_unsigned_t and number_float_t throw")
+    {
+        CHECK_THROWS_WITH_AS(t.get<json::number_integer_t>(), "[json.exception.type_error.302] type must be number, but is boolean", json::type_error&);
+        CHECK_THROWS_WITH_AS(t.get<json::number_unsigned_t>(), "[json.exception.type_error.302] type must be number, but is boolean", json::type_error&);
+        CHECK_THROWS_WITH_AS(t.get<json::number_float_t>(), "[json.exception.type_error.302] type must be number, but is boolean", json::type_error&);
+        CHECK_THROWS_WITH_AS(f.get<json::number_integer_t>(), "[json.exception.type_error.302] type must be number, but is boolean", json::type_error&);
+        CHECK_THROWS_WITH_AS(f.get<json::number_unsigned_t>(), "[json.exception.type_error.302] type must be number, but is boolean", json::type_error&);
+        CHECK_THROWS_WITH_AS(f.get<json::number_float_t>(), "[json.exception.type_error.302] type must be number, but is boolean", json::type_error&);
+    }
+#endif
+}
+
 #ifdef JSON_HAS_CPP_14
     #undef JSON_HAS_CPP_14
 #endif

tests/src/unit-guard-page.cpp

@@ -403,6 +403,7 @@ TEST_CASE("guard page")
                     CHECK(nlohmann::detail::find_string_special(p, n) <= n);
                     CHECK(nlohmann::detail::find_ascii_copyable_run(p, n) <= n);
                     CHECK(nlohmann::detail::valid_utf8_prefix(p, n) <= n);
+                    CHECK(nlohmann::detail::valid_utf8_string(p, n) == (nlohmann::detail::valid_utf8_prefix(p, n) == n));
 #if defined(JSON_USE_SIMDUTF) && defined(JSON_HAS_CPP_17)
                     CHECK(nlohmann::detail::find_string_delimiter(p, n) <= n);
 #endif

tests/src/unit-json_view.cpp

@@ -225,7 +225,7 @@ TEST_CASE("json_view")
 #if JSON_DIAGNOSTICS
         // the parents are set, so errors name the path
         const json m = materialized<json_document>(R"({"a":{"b":[1]}})");
-        CHECK_THROWS_WITH_AS(m.at("a").at("b").at(0).at("x"), "[json.exception.type_error.304] (/a/b/0) cannot use at() with number", json::type_error&);
+        CHECK_THROWS_WITH_AS(m.at("a").at("b").at(0).at("x"), json_view_test::message("type_error.304", "/a/b/0", 11, 12, "cannot use at() with number").c_str(), json::type_error&);
 #endif
     }
 
@@ -750,19 +750,6 @@ std::string exception_of(F f)
     return "";
 }
 
-// the exception a call on a basic_json value throws, without the byte range of
-// the value (JSON_DIAGNOSTIC_POSITIONS), which the exceptions of views lack
-template<typename F>
-std::string json_exception_of(F f)
-{
-    std::string what = exception_of(f);
-    const std::size_t at = what.find("] (bytes ");
-    if (at != std::string::npos)
-    {
-        what.erase(at + 2, what.find(") ", at) - at);
-    }
-    return what;
-}
 #endif
 
 // compares a view with the ordered_json value materialize() gives for it:
@@ -971,24 +958,25 @@ TEST_CASE("json_view element access and iteration")
 #if !defined(JSON_NOEXCEPTION)
             if (!j.is_object())
             {
-                CHECK(exception_of([&] { static_cast<void>(v["a"]); }) == json_exception_of([&] { static_cast<void>(j["a"]); }));
+                CHECK(exception_of([&] { static_cast<void>(v["a"]); }) == exception_of([&] { static_cast<void>(j["a"]); }));
             }
             if (!j.is_array())
             {
-                CHECK(exception_of([&] { static_cast<void>(v[0]); }) == json_exception_of([&] { static_cast<void>(j[0]); }));
+                CHECK(exception_of([&] { static_cast<void>(v[0]); }) == exception_of([&] { static_cast<void>(j[0]); }));
             }
-            CHECK(exception_of([&] { static_cast<void>(v.at("a")); }) == json_exception_of([&] { static_cast<void>(j.at("a")); }));
+            CHECK(exception_of([&] { static_cast<void>(v.at("a")); }) == exception_of([&] { static_cast<void>(j.at("a")); }));
-            CHECK(exception_of([&] { static_cast<void>(v.at("missing")); }) == json_exception_of([&] { static_cast<void>(j.at("missing")); }));
+            CHECK(exception_of([&] { static_cast<void>(v.at("missing")); }) == exception_of([&] { static_cast<void>(j.at("missing")); }));
-            CHECK(exception_of([&] { static_cast<void>(v.at(0)); }) == json_exception_of([&] { static_cast<void>(j.at(0)); }));
+            CHECK(exception_of([&] { static_cast<void>(v.at(0)); }) == exception_of([&] { static_cast<void>(j.at(0)); }));
-            CHECK(exception_of([&] { static_cast<void>(v.at(5)); }) == json_exception_of([&] { static_cast<void>(j.at(5)); }));
+            CHECK(exception_of([&] { static_cast<void>(v.at(5)); }) == exception_of([&] { static_cast<void>(j.at(5)); }));
             if (!(j.is_object() && j.empty())) // (key() of an end iterator)
             {
-                CHECK(exception_of([&] { static_cast<void>(v.begin().key()); }) == json_exception_of([&] { static_cast<void>(j.begin().key()); }));
+                // (without the context of basic_json: view iterators do not know the value they iterate over)
+                CHECK(exception_of([&] { static_cast<void>(v.begin().key()); }) == (j.is_object() ? "" : "[json.exception.invalid_iterator.207] cannot use key() for non-object iterators"));
             }
             if (!j.empty() || j.is_null())
             {
-                CHECK(exception_of([&] { static_cast<void>(v.front()); }) == json_exception_of([&] { static_cast<void>(j.front()); }));
+                CHECK(exception_of([&] { static_cast<void>(v.front()); }) == exception_of([&] { static_cast<void>(j.front()); }));
-                CHECK(exception_of([&] { static_cast<void>(v.back()); }) == json_exception_of([&] { static_cast<void>(j.back()); }));
+                CHECK(exception_of([&] { static_cast<void>(v.back()); }) == exception_of([&] { static_cast<void>(j.back()); }));
             }
 #endif
             CHECK(v.contains("a") == j.contains("a"));
@@ -1000,8 +988,8 @@ TEST_CASE("json_view element access and iteration")
         const json_document d = json_document::parse(R"({"a":[]})");
         CHECK(d.root()["b"].is_discarded());
         CHECK(d.root()["a"][0].is_discarded());
-        CHECK_THROWS_WITH_AS(d.root()["a"].front(), "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
+        CHECK_THROWS_WITH_AS(d.root()["a"].front(), json_view_test::message("invalid_iterator.214", "/a", 5, 7, "cannot get value").c_str(), json::invalid_iterator&);
-        CHECK_THROWS_WITH_AS(d.root()["a"].back(), "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
+        CHECK_THROWS_WITH_AS(d.root()["a"].back(), json_view_test::message("invalid_iterator.214", "/a", 5, 7, "cannot get value").c_str(), json::invalid_iterator&);
         const json_view invalid{};
         CHECK(invalid.begin() == invalid.end());
         CHECK(std::string(invalid.type_name()) == "discarded");
@@ -1032,10 +1020,10 @@ TEST_CASE("json_view element access and iteration")
         CHECK(v[json_view::json_pointer("/a/b/5")][0].is_discarded());
 #if !defined(JSON_NOEXCEPTION)
         // type errors on values that are not discarded stay
-        CHECK_THROWS_WITH_AS(v[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with object", json::type_error&);
+        CHECK_THROWS_WITH_AS(v[0], json_view_test::message("type_error.305", "", 0, 29, "cannot use operator[] with a numeric argument with object").c_str(), json::type_error&);
-        CHECK_THROWS_WITH_AS(v["a"]["b"]["c"], "[json.exception.type_error.305] cannot use operator[] with a string argument with array", json::type_error&);
+        CHECK_THROWS_WITH_AS(v["a"]["b"]["c"], json_view_test::message("type_error.305", "/a/b", 10, 17, "cannot use operator[] with a string argument with array").c_str(), json::type_error&);
-        CHECK_THROWS_WITH_AS(v["s"]["c"], "[json.exception.type_error.305] cannot use operator[] with a string argument with string", json::type_error&);
+        CHECK_THROWS_WITH_AS(v["s"]["c"], json_view_test::message("type_error.305", "/s", 23, 28, "cannot use operator[] with a string argument with string").c_str(), json::type_error&);
-        CHECK_THROWS_WITH_AS(v["s"][0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with string", json::type_error&);
+        CHECK_THROWS_WITH_AS(v["s"][0], json_view_test::message("type_error.305", "/s", 23, 28, "cannot use operator[] with a numeric argument with string").c_str(), json::type_error&);
         CHECK_THROWS_AS(v["a"]["b"][0]["c"], json::type_error&);
         CHECK_THROWS_AS(v["s"][json_view::json_pointer("/x")], json::out_of_range&);
         // at() keeps throwing on a discarded view
@@ -1110,9 +1098,9 @@ TEST_CASE("json_view element access and iteration")
         CHECK(v[(std::numeric_limits<std::size_t>::max)()].is_discarded());
         CHECK(v[std::numeric_limits<int>::max()].is_discarded());
 #if !defined(JSON_NOEXCEPTION)
-        CHECK_THROWS_WITH_AS(v.at(3), "[json.exception.out_of_range.401] array index 3 is out of range", json::out_of_range&);
+        CHECK_THROWS_WITH_AS(v.at(3), json_view_test::message("out_of_range.401", "", 0, 10, "array index 3 is out of range").c_str(), json::out_of_range&);
-        CHECK_THROWS_WITH_AS(v.at(3u), "[json.exception.out_of_range.401] array index 3 is out of range", json::out_of_range&);
+        CHECK_THROWS_WITH_AS(v.at(3u), json_view_test::message("out_of_range.401", "", 0, 10, "array index 3 is out of range").c_str(), json::out_of_range&);
-        CHECK_THROWS_WITH_AS(v.at(std::int64_t(3)), "[json.exception.out_of_range.401] array index 3 is out of range", json::out_of_range&);
+        CHECK_THROWS_WITH_AS(v.at(std::int64_t(3)), json_view_test::message("out_of_range.401", "", 0, 10, "array index 3 is out of range").c_str(), json::out_of_range&);
         CHECK_THROWS_AS(v.at(-1), json::out_of_range&);
         CHECK_THROWS_AS(v.at(-1L), json::out_of_range&);
         CHECK_THROWS_AS(v.at(std::int64_t(-1)), json::out_of_range&);
@@ -1246,26 +1234,6 @@ TEST_CASE("json_view element access and iteration")
 
 namespace
 {
-#if !defined(JSON_NOEXCEPTION)
-// an exception message without the context that basic_json adds with
-// JSON_DIAGNOSTICS ("(/path) ") and JSON_DIAGNOSTIC_POSITIONS ("(bytes 1-2) ");
-// the view's exceptions have no such context
-std::string without_path(std::string msg)
-{
-    for (const char* prefix :
-            {"] (/", "] (bytes "
-            })
-    {
-        const std::size_t open = msg.find(prefix);
-        if (open != std::string::npos)
-        {
-            msg.erase(open + 2, msg.find(") ", open) + 2 - (open + 2));
-        }
-    }
-    return msg;
-}
-#endif
-
 // the bits of a float, to compare values bit for bit
 std::uint64_t bits(double x)
 {
@@ -1336,18 +1304,18 @@ void check_values(const ordered_json_view& v, const ordered_json& j, const std::
     // conversions to the wrong type throw what basic_json throws
     if (!j.is_number())
     {
-        CHECK(exception_of([&] { static_cast<void>(v.get<int>()); }) == without_path(exception_of([&] { static_cast<void>(j.get<int>()); })));
+        CHECK(exception_of([&] { static_cast<void>(v.get<int>()); }) == exception_of([&] { static_cast<void>(j.get<int>()); }));
     }
-    CHECK(exception_of([&] { static_cast<void>(v.get<bool>()); }) == without_path(exception_of([&] { static_cast<void>(j.get<bool>()); })));
+    CHECK(exception_of([&] { static_cast<void>(v.get<bool>()); }) == exception_of([&] { static_cast<void>(j.get<bool>()); }));
-    CHECK(exception_of([&] { static_cast<void>(v.get<std::string>()); }) == without_path(exception_of([&] { static_cast<void>(j.get<std::string>()); })));
+    CHECK(exception_of([&] { static_cast<void>(v.get<std::string>()); }) == exception_of([&] { static_cast<void>(j.get<std::string>()); }));
-    CHECK(exception_of([&] { static_cast<void>(v.get<std::nullptr_t>()); }) == without_path(exception_of([&] { static_cast<void>(j.get<std::nullptr_t>()); })));
+    CHECK(exception_of([&] { static_cast<void>(v.get<std::nullptr_t>()); }) == exception_of([&] { static_cast<void>(j.get<std::nullptr_t>()); }));
     if (!j.is_array())
     {
-        CHECK(exception_of([&] { static_cast<void>(v.get<std::vector<int>>()); }) == without_path(exception_of([&] { static_cast<void>(j.get<std::vector<int>>()); })));
+        CHECK(exception_of([&] { static_cast<void>(v.get<std::vector<int>>()); }) == exception_of([&] { static_cast<void>(j.get<std::vector<int>>()); }));
     }
     if (!j.is_object())
     {
-        CHECK(exception_of([&] { static_cast<void>(v.get<std::map<std::string, int>>()); }) == without_path(exception_of([&] { static_cast<void>(j.get<std::map<std::string, int>>()); })));
+        CHECK(exception_of([&] { static_cast<void>(v.get<std::map<std::string, int>>()); }) == exception_of([&] { static_cast<void>(j.get<std::map<std::string, int>>()); }));
     }
 #endif
 
@@ -1490,8 +1458,8 @@ TEST_CASE("json_view values")
         CHECK(v[3].number_token() == "123456789012345678901234567890");
         CHECK(v[4].number_token() == "-12");
         CHECK(v[5].number_token() == "7");
-        CHECK_THROWS_WITH_AS(v[6].number_token(), "[json.exception.type_error.302] type must be number, but is string", json::type_error&);
+        CHECK_THROWS_WITH_AS(v[6].number_token(), json_view_test::message("type_error.302", "/6", 56, 59, "type must be number, but is string").c_str(), json::type_error&);
-        CHECK_THROWS_WITH_AS(v.get_string(), "[json.exception.type_error.302] type must be string, but is array", json::type_error&);
+        CHECK_THROWS_WITH_AS(v.get_string(), json_view_test::message("type_error.302", "", 0, 60, "type must be string, but is array").c_str(), json::type_error&);
     }
 
     SECTION("conversions")
@@ -1565,15 +1533,15 @@ TEST_CASE("json_view values")
         CHECK(v["o"]["x"].value(json::json_pointer("/1"), 0) == j["o"]["x"].value(json::json_pointer("/1"), 0));
         CHECK(v["o"]["x"].value(json::json_pointer("/7"), 3) == j["o"]["x"].value(json::json_pointer("/7"), 3));
 #if !defined(JSON_NOEXCEPTION)
-        CHECK(exception_of([&] { static_cast<void>(v["o"]["x"].value("k", 0)); }) == without_path(exception_of([&] { static_cast<void>(j["o"]["x"].value("k", 0)); })));
+        CHECK(exception_of([&] { static_cast<void>(v["o"]["x"].value("k", 0)); }) == exception_of([&] { static_cast<void>(j["o"]["x"].value("k", 0)); }));
-        CHECK(exception_of([&] { static_cast<void>(v.value("s", 0)); }) == without_path(exception_of([&] { static_cast<void>(j.value("s", 0)); })));
+        CHECK(exception_of([&] { static_cast<void>(v.value("s", 0)); }) == exception_of([&] { static_cast<void>(j.value("s", 0)); }));
-        CHECK(exception_of([&] { static_cast<void>(v["n"].value("x", 0)); }) == without_path(exception_of([&] { static_cast<void>(j["n"].value("x", 0)); })));
+        CHECK(exception_of([&] { static_cast<void>(v["n"].value("x", 0)); }) == exception_of([&] { static_cast<void>(j["n"].value("x", 0)); }));
-        CHECK(exception_of([&] { static_cast<void>(v["n"].value(json::json_pointer("/x"), 0)); }) == without_path(exception_of([&] { static_cast<void>(j["n"].value(json::json_pointer("/x"), 0)); })));
+        CHECK(exception_of([&] { static_cast<void>(v["n"].value(json::json_pointer("/x"), 0)); }) == exception_of([&] { static_cast<void>(j["n"].value(json::json_pointer("/x"), 0)); }));
         // string defaults: the member is not a string, or the value is neither an object nor an array
-        CHECK(exception_of([&] { static_cast<void>(v.value("n", "default")); }) == without_path(exception_of([&] { static_cast<void>(j.value("n", "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v.value("n", "default")); }) == exception_of([&] { static_cast<void>(j.value("n", "default")); }));
-        CHECK(exception_of([&] { static_cast<void>(v["n"].value("x", "default")); }) == without_path(exception_of([&] { static_cast<void>(j["n"].value("x", "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v["n"].value("x", "default")); }) == exception_of([&] { static_cast<void>(j["n"].value("x", "default")); }));
-        CHECK(exception_of([&] { static_cast<void>(v.value(json::json_pointer("/n"), "default")); }) == without_path(exception_of([&] { static_cast<void>(j.value(json::json_pointer("/n"), "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v.value(json::json_pointer("/n"), "default")); }) == exception_of([&] { static_cast<void>(j.value(json::json_pointer("/n"), "default")); }));
-        CHECK(exception_of([&] { static_cast<void>(v["s"].value(json::json_pointer("/x"), "default")); }) == without_path(exception_of([&] { static_cast<void>(j["s"].value(json::json_pointer("/x"), "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v["s"].value(json::json_pointer("/x"), "default")); }) == exception_of([&] { static_cast<void>(j["s"].value(json::json_pointer("/x"), "default")); }));
 #endif
         // (defaults and members longer than the short string optimization)
         CHECK(v.value("s", "a default longer than fifteen characters") == "text");
@@ -1583,6 +1551,85 @@ TEST_CASE("json_view values")
     }
 }
 
+namespace
+{
+// get<T>() of a boolean: the same value or the same exception in basic_json and in the view (#5988)
+template<typename T>
+void check_boolean_get_parity()
+{
+    for (const bool b :
+            {
+                true, false
+            })
+    {
+        const std::string text = b ? "true" : "false";
+        const json j = json::parse(text);
+        const json_document d = json_document::parse(text);
+        CAPTURE(text)
+#if !defined(JSON_NOEXCEPTION)
+        T dom_value {};
+        T view_value{};
+        const std::string dom_error = json_view_test::exception_of_call([&] { dom_value = j.get<T>(); });
+        const std::string view_error = json_view_test::exception_of_call([&] { view_value = d.root().template get<T>(); });
+        CHECK(dom_error == view_error);
+        if (dom_error.empty())
+        {
+            CHECK(dom_value == view_value);
+            CHECK(view_value == static_cast<T>(b));
+        }
+#else
+        // without exceptions, the combinations that throw (number_integer_t, number_unsigned_t, number_float_t)
+        // cannot be run: JSON_THROW aborts
+        const bool throws = std::is_same<T, json::number_integer_t>::value
+                            || std::is_same<T, json::number_unsigned_t>::value
+                            || std::is_same<T, json::number_float_t>::value;
+        if (!throws)
+        {
+            CHECK(j.get<T>() == d.root().template get<T>());
+        }
+#endif
+    }
+}
+} // namespace
+
+TEST_CASE("json_view get<T>() of a boolean (#5988)")
+{
+    check_boolean_get_parity<bool>();
+    check_boolean_get_parity<char>();
+    check_boolean_get_parity<signed char>();
+    check_boolean_get_parity<unsigned char>();
+    check_boolean_get_parity<short>(); // NOLINT(google-runtime-int)
+    check_boolean_get_parity<unsigned short>(); // NOLINT(google-runtime-int)
+    check_boolean_get_parity<int>();
+    check_boolean_get_parity<unsigned>();
+    check_boolean_get_parity<long>(); // NOLINT(google-runtime-int)
+    check_boolean_get_parity<unsigned long>(); // NOLINT(google-runtime-int)
+    check_boolean_get_parity<long long>(); // NOLINT(google-runtime-int)
+    check_boolean_get_parity<unsigned long long>(); // NOLINT(google-runtime-int)
+    check_boolean_get_parity<std::int64_t>();
+    check_boolean_get_parity<std::uint64_t>();
+    check_boolean_get_parity<float>();
+    check_boolean_get_parity<double>();
+    check_boolean_get_parity<long double>();
+
+#if !defined(JSON_NOEXCEPTION)
+    SECTION("the exceptions of the exact number types")
+    {
+        const json_document d = json_document::parse("true");
+        CHECK_THROWS_WITH_AS(d.root().get<json::number_integer_t>(), json_view_test::message("type_error.302", "", 0, 4, "type must be number, but is boolean").c_str(), json::type_error&);
+        CHECK_THROWS_WITH_AS(d.root().get<json::number_unsigned_t>(), json_view_test::message("type_error.302", "", 0, 4, "type must be number, but is boolean").c_str(), json::type_error&);
+        CHECK_THROWS_WITH_AS(d.root().get<json::number_float_t>(), json_view_test::message("type_error.302", "", 0, 4, "type must be number, but is boolean").c_str(), json::type_error&);
+        CHECK(d.root().get<int>() == 1);
+        // get_to() and value() go through get<T>()
+        json::number_float_t x = 0;
+        CHECK_THROWS_AS(d.root().get_to(x), json::type_error&);
+        const json_document o = json_document::parse("{\"b\":true}");
+        CHECK_THROWS_AS(static_cast<void>(o.root().value("b", 0.0)), json::type_error&);
+        CHECK(o.root().value("b", 0) == 1);
+    }
+#endif
+}
+
 TEST_CASE("json_view JSON pointers")
 {
     SECTION("every value of generated documents")
@@ -1632,7 +1679,7 @@ TEST_CASE("json_view JSON pointers")
         {
             CAPTURE(pointer)
             const json::json_pointer p(pointer);
-            const std::string at_error = without_path(exception_of([&] { static_cast<void>(j.at(p)); }));
+            const std::string at_error = exception_of([&] { static_cast<void>(j.at(p)); });
             CHECK(exception_of([&] { static_cast<void>(v.at(p)); }) == at_error);
             if (at_error.empty())
             {
@@ -1646,7 +1693,7 @@ TEST_CASE("json_view JSON pointers")
             }
             else
             {
-                CHECK(exception_of([&] { static_cast<void>(v[p]); }) == without_path(exception_of([&] { static_cast<void>(j[p]); })));
+                CHECK(exception_of([&] { static_cast<void>(v[p]); }) == exception_of([&] { static_cast<void>(j[p]); }));
             }
             // (basic_json::contains() throws out_of_range.404 for an empty
             // array index token, although it is not meant to throw; the view
@@ -1657,7 +1704,7 @@ TEST_CASE("json_view JSON pointers")
                 static_cast<void>(found);
             });
             CHECK(v.contains(p) == (contains_error.empty() && j.contains(p)));
-            CHECK(exception_of([&] { static_cast<void>(v.value(p, 5)); }) == without_path(exception_of([&] { static_cast<void>(j.value(p, 5)); })));
+            CHECK(exception_of([&] { static_cast<void>(v.value(p, 5)); }) == exception_of([&] { static_cast<void>(j.value(p, 5)); }));
         }
     }
 #endif

tests/src/unit-json_view_builder.cpp

@@ -13,6 +13,7 @@
     #include <nlohmann/detail/view/builder.hpp>
     #include <nlohmann/detail/view/materialize.hpp>
     #include <nlohmann/detail/view/string_ref.hpp>
+    #include <nlohmann/json_view.hpp> // json_document::accept
 #else
     #include <nlohmann/json_view.hpp> // the single header contains the internal headers
 #endif
@@ -59,7 +60,8 @@ built build(const std::string& text, bool comments, bool trailing_commas, bool s
         r.copy.assign(text.begin(), text.end());
         src = r.copy.data();
     }
-    r.ok = nlohmann::detail::view::build < FloatType, !nlohmann::detail::abi_config::strict_nul_handling > (*r.data, src, text.size(), comments, trailing_commas, sentinel, r.failure);
+    constexpr bool nul_is_end = !nlohmann::detail::abi_config::strict_nul_handling;
+    r.ok = nlohmann::detail::view::build<FloatType, nul_is_end>(*r.data, src, text.size(), comments, trailing_commas, sentinel, false, r.failure);
     r.data->src = src;
     r.data->base[0] = src;
     r.data->base[1] = r.data->arena.data();
@@ -172,6 +174,22 @@ void check_string(const std::string& content)
     }
 }
 
+// accept() stores no nodes: it must accept and reject what json::accept does, for all options and for inputs with
+// and without a terminating NUL
+void check_accept(const std::string& text)
+{
+    CAPTURE(text)
+    const std::vector<char> bytes(text.begin(), text.end());
+    for (int options = 0; options < 4; ++options)
+    {
+        const bool comments = (options & 1) != 0;
+        const bool trailing_commas = (options & 2) != 0;
+        const bool accepted = json::accept(text, comments, trailing_commas);
+        CHECK(nlohmann::json_document::accept(text, comments, trailing_commas) == accepted);
+        CHECK(nlohmann::json_document::accept(bytes, comments, trailing_commas) == accepted);
+    }
+}
+
 // a small deterministic generator of documents
 struct generator
 {
@@ -423,6 +441,133 @@ TEST_CASE("json_view builder")
         }
     }
 
+    SECTION("accept() without an index")
+    {
+        for (const char* text :
+                {
+                    "", " ", "\n", "null", "nul", "true", "[", "]", "[]", "{}", "[1,2,3]", "[1,2,3", "[1,2,3,]", "{\"a\":1,}", "{\"a\"}", "{\"a\":}",
+                    "[1] x", "[1][2]", "\xEF\xBB\xBF[1]", "[\"a\\", R"(["\u12"])", R"(["\ud800"])", "[\"\x01\"]", "[\"\xff\"]", "[01]", "[1.]",
+                    "[.5]", "[-]", "[1e]", "// c\n[1]", "/* c */ {\"a\" /* x */ : 1}", "/* c", "[1] // c", "1e400", "-1e400", "123456789012345678901234567890",
+                    R"({"a":1,"a":2})", "[[[]]]", R"("\u00e4\n\ud83d\ude00")"
+                })
+        {
+            check_accept(text);
+        }
+        // a null byte inside the text, and after it
+        check_accept(std::string("[1,\0]", 5));
+        check_accept(std::string("[1]\0", 4));
+        check_accept(std::string("\0", 1));
+
+        // generated documents and damaged copies, as for the builder above
+        generator g;
+        for (int i = 0; i < 2000; ++i)
+        {
+            std::string text;
+            g.value(text, 0);
+            check_accept(text);
+            std::string damaged = text;
+            const auto at = static_cast<std::size_t>(g.r(static_cast<int>(damaged.size())));
+            static const char replacements[] = {'x', '"', '\\', ',', ':', ']', '}', '[', '{', '1', '-', '.', 'e', '\0', '\n', '/'}; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+            damaged[at] = replacements[g.r(16)];
+            check_accept(damaged);
+            check_accept(text.substr(0, at));
+        }
+
+        // nesting beyond the 64 levels that are kept on the builder's own stack, closed and not closed
+        for (const std::size_t depth :
+                {
+                    63u, 64u, 65u, 66u, 200u, 1000u
+                })
+        {
+            check_accept(std::string(depth, '[') + std::string(depth, ']'));
+            check_accept(std::string(depth, '[') + std::string(depth - 1, ']'));
+            std::string objects;
+            for (std::size_t i = 0; i < depth; ++i)
+            {
+                objects += "{\"k\":";
+            }
+            objects += "1" + std::string(depth, '}');
+            check_accept(objects);
+            check_accept(objects.substr(0, objects.size() - 1));
+        }
+
+        // objects with enough members to get a hash index when they are indexed (and duplicate keys)
+        std::string large = "{";
+        for (int i = 0; i < 300; ++i)
+        {
+            large += (i == 0 ? "\"k" : ",\"k") + std::to_string(i % 200) + "\":" + std::to_string(i);
+        }
+        check_accept(large + "}");
+        check_accept(large);
+        check_accept("[" + large + "},{" + large.substr(1) + "}]");
+
+        // the overflow check uses the floating-point type of the document
+        using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
+        for (const char* text :
+                {
+                    "1e39", "-1e39", "3.4028235e38", "3.4028236e38", "[1.5e38, 3.5e38]", R"({"a": 1e-50, "b": 1e39})", "340282356779733661637539395458142568448"
+                })
+        {
+            CAPTURE(text)
+            CHECK(nlohmann::basic_json_document<float_json>::accept(text) == float_json::accept(text));
+        }
+
+        // strings are checked and not decoded: runs of text of every length from 0 to 40 between valid and invalid
+        // escapes, UTF-8 sequences and control characters, in values and in keys, cut near the end of the text
+        const std::array<const char*, 9> valid = {{"\\n", "\\\"", "\\\\", "\\/", "\\t", "\\u00e4", "\\u20ac", "\\ud83d\\ude00", "\\u0000"}};
+        const std::array<const char*, 12> invalid = {{"\\x", "\\ud800", "\\udc00", "\\u12G4", "\\u12", "\\ud83dx", "\\ud83d\\u0041", "\\ud83d\\ud83d", "\\", "\x01", "\x1f", "\x7f"}};
+        const std::array<const char*, 6> utf8 = {{"\xc3\xa4", "\xe2\x82\xac", "\xf0\x9f\x98\x80", "\xc3", "\xff", "\x80"}};
+        std::mt19937 rng(2029); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed): reproducible
+        for (std::size_t run = 0; run <= 40; ++run)
+        {
+            for (int i = 0; i < 30; ++i)
+            {
+                std::string content = std::string(rng() % 20, 'a');
+                const auto pieces = 1 + (rng() % 6);
+                for (unsigned k = 0; k < pieces; ++k)
+                {
+                    content += valid[rng() % valid.size()];
+                    content += std::string(k == 0 ? run : rng() % 41, static_cast<char>('b' + (rng() % 20)));
+                    switch (rng() % 8)
+                    {
+                        case 0:
+                            content += utf8[rng() % 3];
+                            break;
+                        case 1:
+                            content += utf8[rng() % utf8.size()];
+                            break;
+                        case 2:
+                            content += invalid[rng() % invalid.size()];
+                            break;
+                        default:
+                            break;
+                    }
+                }
+                for (const std::string& text :
+                        {
+                            "[\"" + content + "\"]", "{\"" + content + "\":1}", "[\"" + content, "[\"" + content.substr(0, content.size() - (rng() % 4)) + "\"]"
+                        })
+                {
+                    check_accept(text);
+                }
+            }
+        }
+    }
+
+    SECTION("escapes in a row")
+    {
+        for (const char* content :
+                {
+                    "\\n", R"(\n\t\\)", R"(\u00e9\u00e9\u4e2d)", "\\u00e9\\u00e", "\\u00e9\\", "\\n\\q", R"(\n\ud83d\ude00\n)",
+                    R"(\ud83d\ude00\ud83d)", R"(\n\n\n abc \n\n)", "\\n\x01", "\\n\xC3\x28", "\\n\\"
+                })
+        {
+            check_accept(std::string("[\"") + content + "\"]");
+            check_accept(std::string("[\"") + content);
+            check_accept(std::string("{\"") + content + "\":1}");
+        }
+    }
+
     SECTION("test files")
     {
         for (const char* name :
@@ -523,6 +668,54 @@ TEST_CASE("json_view builder: strings across vector blocks")
     }
 }
 
+TEST_CASE("json_view builder: fraction digits")
+{
+    // The digits of a fraction are skipped 16 bytes at a time where there are
+    // that many left (SSE2), and one at a time after that. Fractions of every
+    // length from 0 to 40 digits, followed by every kind of byte that ends a
+    // number or lies next to the digits in ASCII ('/' and ':'), as values, as
+    // keys' neighbours, and at the very end of the text (a vector without a
+    // terminating NUL). The length of the number is part of the value that
+    // the test compares with json::parse().
+    const std::string followers = ",]}/:.eE+-x \n\t\"09";
+    std::mt19937 rng(2028); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed): reproducible
+    for (std::size_t digits = 0; digits <= 40; ++digits)
+    {
+        for (int i = 0; i < 3; ++i)
+        {
+            std::string fraction;
+            for (std::size_t k = 0; k < digits; ++k)
+            {
+                fraction += static_cast<char>('0' + (rng() % 10));
+            }
+            const std::string number = std::string(rng() % 2 == 0 ? "-" : "") + std::to_string(rng() % 100000) + "." + fraction;
+            check_same(number);
+            check_same("[" + number + "]");
+            std::string pair;
+            pair.reserve(number.size() * 2 + 3);
+            pair += '[';
+            pair += number;
+            pair += ',';
+            pair += number;
+            pair += ']';
+            check_same(pair);
+            check_same("{\"a\":" + number + "}");
+            for (const char follower : followers)
+            {
+                check_same(number + follower);
+                check_same("[" + number + follower + "]");
+                check_same("[" + number + follower + std::string(rng() % 20, '1'));
+            }
+            // everything near the end of the text: the number cut in every place
+            for (std::size_t cut = 1; cut <= 18 && cut <= number.size(); ++cut)
+            {
+                check_same(number.substr(0, number.size() - cut));
+                check_same("[" + number.substr(0, number.size() - cut));
+            }
+        }
+    }
+}
+
 TEST_CASE("json_view builder: escapes between runs of text")
 {
     // The text between escapes is copied 16 bytes at a time where there are
@@ -575,6 +768,59 @@ TEST_CASE("json_view builder: escapes between runs of text")
     }
 }
 
+TEST_CASE("json_view builder: chains of unicode escapes")
+{
+    // Consecutive \uXXXX escapes are decoded in a loop of their own. Chains of
+    // every length from 1 to 40 of escapes that give one, two, and three
+    // bytes of UTF-8, in upper and lower case, followed by what ends a chain:
+    // the end of the string, text, another escape, UTF-8, and everything that
+    // is not a valid escape (a bad digit at every position of the last
+    // escape, a lone surrogate, a surrogate pair, a cut in every place).
+    const std::array<const char*, 8> chain = {{"\\u0041", "\\u00e4", "\\u00E4", "\\u20ac", "\\u3042", "\\uFFFF", "\\u0000", "\\u07ff"}};
+    const std::array<const char*, 12> ends = {{"", "abc", "\\n", "\\u00e9", "\\ud83d\\ude00", "\\ud83d", "\\ude00", "\\ud83d\\u0041", "\\u12G4", "\\u12", "\xc3\xa4", "\\"}};
+    std::mt19937 rng(2027); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed): reproducible
+    for (std::size_t length = 1; length <= 40; ++length)
+    {
+        for (int i = 0; i < 20; ++i)
+        {
+            std::string content = std::string(rng() % 20, 'a');
+            for (std::size_t k = 0; k < length; ++k)
+            {
+                content += chain[rng() % chain.size()];
+            }
+            const std::string whole = content;
+            for (const char* end : ends)
+            {
+                check_string(whole + end);
+                check_string(whole + end + std::string(rng() % 19, 'z'));
+            }
+            // a bad digit at every position of every escape near the end of the chain
+            for (std::size_t back = 1; back <= 6 && back <= length; ++back)
+            {
+                for (std::size_t digit = 2; digit < 6; ++digit)
+                {
+                    std::string broken = whole;
+                    broken[broken.size() - (6 * back) + digit] = "gG\"\x01 z"[rng() % 6];
+                    check_string(broken);
+                }
+            }
+            // the text cut in every place of the last three escapes
+            for (std::size_t cut = 0; cut <= 18 && cut <= whole.size(); ++cut)
+            {
+                check_string(whole.substr(0, whole.size() - cut));
+            }
+        }
+    }
+    // a chain longer than the first growth of the arena, in a key and in a value
+    std::string long_chain;
+    for (int i = 0; i < 3000; ++i)
+    {
+        long_chain += chain[static_cast<std::size_t>(i) % chain.size()];
+    }
+    check_string(long_chain);
+    check_string(long_chain + "\\ud83d\\ude00" + long_chain);
+}
+
 TEST_CASE("json_view node integer bits")
 {
     using nlohmann::detail::view::integer_bits;

tests/src/unit-json_view_dump.cpp

@@ -35,9 +35,9 @@ using json_view_test::has_duplicate_keys;
 #include <string>
 #include <vector>
 
-// These tests were split off unit-json_view.cpp, whose object file got too large
+// These tests were split off unit-json_view.cpp, whose object file got too large for the MinGW
-// for the MinGW linker (see json_view_test_helpers.hpp). Like that file, this one
+// linker (see json_view_test_helpers.hpp). Like that file, this one is also built
-// is also built with C++17, as it mentions JSON_HAS_CPP_17.
+// with C++17, as it mentions JSON_HAS_CPP_17.
 
 TEST_CASE("json_view dump")
 {
@@ -150,6 +150,88 @@ TEST_CASE("json_view dump")
             CHECK(many_doc.root().dump() == json::parse(many_tokens).dump());
         }
 
+        // tokens of 16 and 17 digits without an exponent (like GeoJSON
+        // coordinates), which dump() converts in batches: doubles exactly
+        // halfway between two candidates for the shortest digits, random
+        // digits, and digits near a shorter decimal (...99999997,
+        // ...00000003), whose rounding carries; in pairs and among other
+        // values, so that the batches are interrupted; the last token near the
+        // end of the text
+        {
+            std::mt19937_64 tokens(5627); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+            const auto draw = [&tokens](std::size_t n)
+            {
+                const std::uint64_t r = tokens() % n;
+                return static_cast<std::size_t>(r);
+            };
+            std::string coordinates = "[754570942.33984373,257769445.56835938,858106901.94921875,97944964.876953125,"
+                                      "[0.5,1e-7],[1.5,-0.0,2.5],[1E2,12.5,0.1,3.25,4.5,5.75,6.125,7.0,8.5],[],[1.5],[1,2.5],[2.5,\"x\"],[[1.5],2.5],";
+            for (int i = 0; i < 20000; ++i)
+            {
+                const std::size_t length = 16 + draw(2);
+                std::string digits(1, static_cast<char>('1' + draw(9)));
+                const std::size_t kept = draw(3) == 0 ? length : 2 + draw(length - 3);
+                for (std::size_t k = 1; k < kept; ++k)
+                {
+                    digits += static_cast<char>('0' + draw(10));
+                }
+                digits += std::string(length - kept, draw(2) == 0 ? '9' : '0');
+                digits.back() = static_cast<char>('0' + draw(10));
+                const std::size_t point = 1 + draw(9);
+                const std::string token = (draw(2) == 0 ? "-" : "") + digits.substr(0, point) + "." + digits.substr(point);
+                if (i != 0)
+                {
+                    coordinates += ',';
+                }
+                if (draw(8) == 0)
+                {
+                    coordinates += R"({"x":)";
+                    coordinates += token;
+                    coordinates += R"(,"s":"a"})";
+                }
+                else
+                {
+                    coordinates += '[';
+                    coordinates += token;
+                    coordinates += ',';
+                    coordinates += token;
+                    coordinates += ']';
+                }
+            }
+            coordinates += ",-65.613616999999977]";
+            const json_document parsed = json_document::parse(coordinates);
+            const ordered_json j = ordered_json::parse(coordinates);
+            CHECK(parsed.root().dump() == j.dump());
+            CHECK(parsed.root().dump(1) == j.dump(1));
+            CHECK(parsed.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+            CHECK(parsed.root().back().get<double>() == j.back().get<double>());
+            CHECK(parsed.root().back().dump() == "-65.61361699999998");
+            std::size_t i = 0;
+            for (const json_view v : parsed.root())
+            {
+                const ordered_json& e = j[i++];
+                CHECK(v.dump() == e.dump());
+                if (v.is_array() && !v.empty() && v[0].is_number())
+                {
+                    CHECK(v[0].get<double>() == e[0].get<double>());
+                }
+            }
+
+            // an editable document: edits move some arrays, so that the walk
+            // leaves the order of the parsed nodes
+            ordered_json_editable_document editable = ordered_json_editable_document::parse(coordinates);
+            ordered_json expected = j;
+            for (std::size_t k = 0; k < 20000; k += 97)
+            {
+                if (expected[k].is_array())
+                {
+                    editable.push_back(editable.root()[k], ordered_json(1.5));
+                    expected[k].push_back(1.5);
+                }
+            }
+            CHECK(editable.root().dump() == expected.dump());
+        }
+
         // random doubles, written as parse() and dump() would
         std::mt19937_64 rng(1170); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
         std::string many = "[";
@@ -171,673 +253,4 @@ TEST_CASE("json_view dump")
         const nlohmann::basic_json_document<json_float> float_document = nlohmann::basic_json_document<json_float>::parse("[0.1, 1.5e10, 3.4028235e38]");
         CHECK(float_document.root().dump() == json_float::parse("[0.1, 1.5e10, 3.4028235e38]").dump());
     }
-
-    SECTION("members in document order, all of them")
-    {
-        const json_document d = json_document::parse(R"({"b": 1, "a": 2, "b": 3})");
-        CHECK(d.root().dump() == R"({"b":1,"a":2,"b":3})");
-        CHECK(d.root().dump(1) == "{\n \"b\": 1,\n \"a\": 2,\n \"b\": 3\n}");
-        // dump() writes all members, though the lookup finds the first
-        CHECK(d.root()["b"].dump() == "1");
-    }
-
-    SECTION("deep nesting")
-    {
-        const std::string deep = std::string(100000, '[') + std::string(100000, ']');
-        const json_document deep_document = json_document::parse(deep);
-        CHECK(deep_document.root().dump() == deep);
-    }
-
-    SECTION("ensure_ascii: a character that needs an escape at each position of a string")
-    {
-        // string lengths around the width of the vector steps, in a string value, a key, and a value near the end of the text
-        for (const char* const special :
-                {
-                    "\xC3\xA9", "\xE4\xB8\xAD", "\xF0\x9F\x98\x80", "\x7F", "\\n", "\\u0001", "\\\"", "\\\\"
-                })
-        {
-            for (std::size_t length = 0; length <= 40; ++length)
-            {
-                for (std::size_t position = 0; position <= length; ++position)
-                {
-                    std::string content(length, 'a');
-                    content.insert(position, special);
-                    const std::array<std::string, 3> texts =
-                    {
-                        {
-                            "\"" + content + "\"",
-                            "[\"" + content + "\"]",
-                            "{\"" + content + "\":1}",
-                        }
-                    };
-                    for (const std::string& text : texts)
-                    {
-                        CAPTURE(text)
-                        const ordered_json_document d = ordered_json_document::parse(text);
-                        const ordered_json j = ordered_json::parse(text);
-                        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
-                        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
-                        CHECK(d.root().dump() == j.dump());
-                    }
-                }
-            }
-        }
-    }
-
-    SECTION("ensure_ascii: every character of the Basic Multilingual Plane and some beyond")
-    {
-        // (the two- and three-byte sequences, including the ranges that need a check: E0, ED, EF BF BF)
-        std::string text = "[";
-        std::size_t in_chunk = 0;
-        const auto append = [&](std::uint32_t cp)
-        {
-            if (cp < 0x80)
-            {
-                if (cp < 0x20 || cp == '"' || cp == '\\')
-                {
-                    return;
-                }
-                text += static_cast<char>(cp);
-            }
-            else if (cp < 0x800)
-            {
-                text += static_cast<char>(0xC0 | (cp >> 6));
-                text += static_cast<char>(0x80 | (cp & 0x3F));
-            }
-            else if (cp < 0x10000)
-            {
-                text += static_cast<char>(0xE0 | (cp >> 12));
-                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
-                text += static_cast<char>(0x80 | (cp & 0x3F));
-            }
-            else
-            {
-                text += static_cast<char>(0xF0 | (cp >> 18));
-                text += static_cast<char>(0x80 | ((cp >> 12) & 0x3F));
-                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
-                text += static_cast<char>(0x80 | (cp & 0x3F));
-            }
-        };
-        for (std::uint32_t cp = 0x20; cp < 0x10400; ++cp)
-        {
-            if (cp >= 0xD800 && cp < 0xE000)
-            {
-                continue;
-            }
-            if (in_chunk == 0)
-            {
-                text += text.size() > 1 ? ",\"" : "\"";
-            }
-            append(cp);
-            if (++in_chunk == 37)
-            {
-                text += "\"";
-                in_chunk = 0;
-            }
-        }
-        text += in_chunk != 0 ? "\"]" : "]";
-        const ordered_json_document d = ordered_json_document::parse(text);
-        const ordered_json j = ordered_json::parse(text);
-        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
-        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
-        CHECK(d.root().dump() == j.dump());
-        CHECK(d.root().dump(2) == j.dump(2));
-    }
-
-    SECTION("deep nesting, indented")
-    {
-        // indentations of up to and beyond the width of the writer's fixed-size copy
-        for (const int depth :
-                {
-                    1, 5, 20, 70, 300
-                })
-        {
-            std::string text;
-            for (int i = 0; i < depth; ++i)
-            {
-                text += i % 2 == 0 ? "[1," : R"({"k":2,"\u00e9":)";
-            }
-            text += "[]";
-            for (int i = depth - 1; i >= 0; --i)
-            {
-                text += i % 2 == 0 ? "]" : "}";
-            }
-            const ordered_json_document d = ordered_json_document::parse(text);
-            const ordered_json j = ordered_json::parse(text);
-            for (const int indent :
-                    {
-                        0, 1, 2, 3, 8
-                    })
-            {
-                CHECK(d.root().dump(indent) == j.dump(indent));
-                CHECK(d.root().dump(indent, '\t') == j.dump(indent, '\t'));
-            }
-        }
-    }
-
-    SECTION("the output buffer of a small value is small")
-    {
-        // an escaped key after the value: its node lies in the arena, so the
-        // source extent of the value cannot be read from the next node
-        const std::string big(100000, 'a');
-        const std::string text = R"({"small":1,"list":[1,2,3],"k\n":")" + big + R"("})";
-        const json_document d = json_document::parse(text);
-        const auto small = d.root()["small"].dump();
-        CHECK(small == "1");
-        CHECK(small.capacity() < 4096);
-        const auto list = d.root()["list"].dump();
-        CHECK(list == "[1,2,3]");
-        CHECK(list.capacity() < 4096);
-        CHECK(d.root()["list"].dump(2).capacity() < 4096);
-
-        // the whole document and the large value are unaffected
-        CHECK(d.root().dump() == ordered_json::parse(text).dump());
-        CHECK(d.root()["k\n"].dump() == "\"" + big + "\"");
-    }
-
-    SECTION("output that outgrows the estimate")
-    {
-        // ensure_ascii writes six bytes for each two-byte character
-        std::string chars;
-        for (int i = 0; i < 5000; ++i)
-        {
-            chars += "\xC3\xA9";
-        }
-        const json_document d = json_document::parse(R"({"a":")" + chars + R"(","k\n":1})");
-        const json expected = json::parse("\"" + chars + "\"");
-        CHECK(d.root()["a"].dump(-1, ' ', true) == expected.dump(-1, ' ', true));
-        CHECK(d.root()["a"].dump(-1, ' ', true).size() == 2 + (5000 * 6));
-    }
-
-    SECTION("ensure_ascii with strings of the source, decoded strings, and edited strings")
-    {
-        // plain ASCII, non-ASCII, escaped (decoded), and mixed strings, as values and as keys;
-        // the second text has a DEL, which ensure_ascii writes as an escape
-        for (const char* const del :
-                {"", "\x7F"
-                })
-        {
-            const std::string text = std::string("{\"plain\":\"abc\",\"caf\xC3\xA9\":\"\xC3\xA9\xE2\x82\xAC\xF0\x9F\x98\x80\",")
-                                     + "\"esc\\n\\\"\":\"a\\tb\\u00e4\\ud83d\\ude00\",\"del\":\"a" + del + "b\",\"\":\"\"," // NOLINT(modernize-raw-string-literal)
-                                     + "\"list\":[\"x\",\"\xC3\xBC\",\"\\\\\",\"long ASCII string with more than thirty-two bytes in it\","
-                                     + "\"long string with more than thirty-two bytes and one non-ASCII byte \xC3\xB6\"],"
-                                     + "\"n\":[1,2.5,-0,true,null]}";
-            const ordered_json j = ordered_json::parse(text);
-            const ordered_json_document d = ordered_json_document::parse(text);
-            CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
-            CHECK(d.root().dump(4, ' ', true) == j.dump(4, ' ', true));
-            CHECK(d.root().dump() == j.dump());
-            CHECK(d.root()["list"].dump(-1, ' ', true) == j["list"].dump(-1, ' ', true));
-            CHECK(d.root()["del"].dump(-1, ' ', true) == j["del"].dump(-1, ' ', true));
-
-            // strings that an edit wrote (the source strings that they replace were plain)
-            ordered_json_editable_document e = ordered_json_editable_document::parse(text);
-            ordered_json k = j;
-            e.set(e.root()["plain"], std::string("\xC3\xA4gypten"));
-            k["plain"] = "\xC3\xA4gypten";
-            e.set(e.root()["list"][0], std::string("ascii after edit"));
-            k["list"][0] = "ascii after edit";
-            e.set(e.root()["list"][1], std::string("\xC3\xA4"));
-            k["list"][1] = "\xC3\xA4";
-            e.set(e.root()["del"], std::string("tab\there"));
-            k["del"] = "tab\there";
-            CHECK(e.root().dump(-1, ' ', true) == k.dump(-1, ' ', true));
-            CHECK(e.root().dump(2, ' ', true) == k.dump(2, ' ', true));
-            CHECK(e.root().dump() == k.dump());
-
-            // strings that were edited from or to ASCII text
-            e.set(e.root()["list"][2], std::string("\xC3\xA4"));
-            k["list"][2] = "\xC3\xA4";
-            e.set(e.root()["list"][4], std::string("plain again"));
-            k["list"][4] = "plain again";
-            CHECK(e.root().dump(-1, ' ', true) == k.dump(-1, ' ', true));
-        }
-    }
-
-    SECTION("ensure_ascii with DEL or a non-ASCII character at every position")
-    {
-        // the check whether a string of the source has no byte >= 0x7F reads
-        // eight bytes at a time and then the rest one by one
-        for (std::size_t length = 1; length <= 20; ++length)
-        {
-            for (std::size_t pos = 0; pos < length; ++pos)
-            {
-                for (const char* const c :
-                        {
-                            "\x7F", "\x7E", "\xC3\xA4", "\xC3\xBF" // NOLINT(modernize-raw-string-literal)
-                        })
-                {
-                    const std::string s = std::string(pos, 'a') + c + std::string(length - pos - 1, 'b');
-                    std::string text = "[\"";
-                    text.append(s).append("\",{\"").append(s).append("\":1}]");
-                    const json_document d = json_document::parse(text);
-                    const json j = json::parse(text);
-                    CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
-                    CHECK(d.root().dump(1, ' ', true) == j.dump(1, ' ', true));
-                }
-            }
-        }
-    }
-
-    SECTION("streams and discarded views")
-    {
-        const json_document d = json_document::parse(R"({"a": [1, 2]})");
-        std::ostringstream compact;
-        compact << d.root();
-        CHECK(compact.str() == R"({"a":[1,2]})");
-        std::ostringstream pretty;
-        pretty << std::setw(2) << std::setfill('.') << d.root() << d.root()["a"];
-        CHECK(pretty.str() == "{\n..\"a\": [\n....1,\n....2\n..]\n}[1,2]");
-        CHECK(json_view().dump() == json(json::value_t::discarded).dump());
-    }
-}
-
-TEST_CASE("json_view large objects")
-{
-    // objects with 128 members or more are looked up with a hash index
-    for (const std::size_t members :
-            {
-                127u, 128u, 129u, 10000u
-            })
-    {
-        CAPTURE(members)
-        std::string text = "{";
-        for (std::size_t i = 0; i < members; ++i)
-        {
-            text += (i != 0 ? ",\"" : "\"") + std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\\n" : "") + "\":" + std::to_string(i);
-        }
-        text += R"(,"":"empty key","k1":"a duplicate of an earlier key"})";
-        const json_document d = json_document::parse(text);
-        const json_view v = d.root();
-        const json j = json::parse(text);
-        for (std::size_t i = 0; i < members; ++i)
-        {
-            const std::string key = std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\n" : "");
-            CHECK(v[key].get<std::size_t>() == i);
-            CHECK(v.contains(key));
-            CHECK(v.find(key).key() == key);
-            CHECK(v.at(key).get<std::size_t>() == i);
-            CHECK(!v.contains(key + "x"));
-        }
-        CHECK(v[""].get_string() == "empty key");
-        CHECK(v["k1"].get<int>() == 1); // the first of duplicate keys, as for small objects
-        CHECK(!v.contains("missing"));
-        CHECK_THROWS_WITH_AS(v.at("missing"), "[json.exception.out_of_range.403] key 'missing' not found", json::out_of_range&);
-        CHECK(v == j);
-        CHECK(v.materialize() == j);
-    }
-
-    SECTION("duplicate keys: the first member wins, with and without a table")
-    {
-        // an object of `total` members: the keys "k0".."k<n-1>" in order, then
-        // three keys repeated twice more (one copy in the middle, one at the
-        // end), and two keys repeated once; the value of a member is its
-        // position, so that the first member of a key can be told apart
-        struct member
-        {
-            std::string key;
-            std::size_t position;
-        };
-        const auto make_members = [](std::size_t total)
-        {
-            std::vector<std::string> keys;
-            for (std::size_t i = 0; i + 8 < total; ++i)
-            {
-                keys.push_back("k" + std::to_string(i));
-            }
-            const std::size_t n = keys.size();
-            const std::array<std::size_t, 3> triple = {{3, 17, n - 1}};
-            const std::array<std::size_t, 2> twice = {{5, n / 2}};
-            std::vector<std::string> ordered = keys;
-            for (const std::size_t i : triple)
-            {
-                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 2), keys[i]);
-            }
-            for (const std::size_t i : twice)
-            {
-                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 3), keys[i]);
-            }
-            for (const std::size_t i : triple)
-            {
-                ordered.push_back(keys[i]);
-            }
-            std::vector<member> result;
-            result.reserve(ordered.size());
-            for (std::size_t i = 0; i < ordered.size(); ++i)
-            {
-                result.push_back({ordered[i], i});
-            }
-            return result;
-        };
-
-        // 100 and 127 members: no table; 128 members and more: a table
-        for (const std::size_t total :
-                {
-                    100u, 127u, 128u, 200u, 5000u
-                })
-        {
-            CAPTURE(total)
-            const std::vector<member> members = make_members(total);
-            REQUIRE(members.size() >= total);
-            REQUIRE(members.size() >= 100);
-            std::string text = "{";
-            std::map<std::string, std::size_t> first;
-            std::map<std::string, std::size_t> last;
-            std::map<std::string, std::size_t> occurrences;
-            for (const member& m : members)
-            {
-                text += (text.size() > 1 ? ",\"" : "\"") + m.key + "\":" + std::to_string(m.position);
-                first.insert({m.key, m.position});
-                last[m.key] = m.position;
-                ++occurrences[m.key];
-            }
-            text += '}';
-            REQUIRE(first.size() < members.size());
-
-            const json_document d = json_document::parse(text);
-            const json_view v = d.root();
-            const json j = json::parse(text);
-            CHECK(v.size() == members.size()); // every occurrence is visited
-            const json m = v.materialize();
-            for (const auto& entry : first)
-            {
-                CAPTURE(entry.first)
-                const std::size_t expected = entry.second;
-                CHECK(v[entry.first].get<std::size_t>() == expected);
-                CHECK(v.at(entry.first).get<std::size_t>() == expected);
-                CHECK(v.find(entry.first).value().get<std::size_t>() == expected);
-                CHECK(v.value(entry.first, std::size_t{0}) == expected);
-                CHECK(v.contains(entry.first));
-                CHECK(v.count(entry.first) == occurrences[entry.first]);
-                const std::string pointer = "/" + entry.first;
-                CHECK(v[json::json_pointer(pointer)].get<std::size_t>() == expected);
-                CHECK(v.at(json::json_pointer(pointer)).get<std::size_t>() == expected);
-                CHECK(v.value(json::json_pointer(pointer), std::size_t{0}) == expected);
-                CHECK(v.contains(json::json_pointer(pointer)));
-                // materialize() and parse() keep the last value instead
-                CHECK(j[entry.first].get<std::size_t>() == last.at(entry.first));
-                CHECK(m[entry.first].get<std::size_t>() == last.at(entry.first));
-            }
-            CHECK(!v.contains("k"));
-            CHECK(v["missing"].is_discarded());
-            CHECK(v.materialize() == j);
-            CHECK(v == j);
-        }
-    }
-
-    SECTION("colliding keys")
-    {
-        // the hash is not seeded, so keys that all land in one place must not
-        // make the table build quadratic: such an object gets no table and is
-        // searched linearly
-        constexpr std::size_t members = 300;
-        constexpr std::size_t table_size = 1024; // the table size for 300 members: the next power of two >= 600
-        std::vector<std::string> colliding;
-        std::vector<std::string> spread;
-        for (std::uint64_t counter = 0; colliding.size() < members || spread.size() < members; ++counter)
-        {
-            std::string key(8, 'a');
-            std::uint64_t x = counter;
-            for (std::size_t i = 0; i < 8; ++i, x /= 26)
-            {
-                key[i] = static_cast<char>('a' + (x % 26));
-            }
-            const bool lands_in_slot_zero = (nlohmann::detail::view::key_hash(key.data(), key.size()) & (table_size - 1)) == 0;
-            if (lands_in_slot_zero && colliding.size() < members)
-            {
-                colliding.push_back(key);
-            }
-            else if (!lands_in_slot_zero && spread.size() < members)
-            {
-                spread.push_back(key);
-            }
-        }
-
-        const auto make_text = [](const std::vector<std::string>& keys)
-        {
-            std::string text = "{";
-            for (std::size_t i = 0; i < keys.size(); ++i)
-            {
-                text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i % 10);
-            }
-            return text + "}";
-        };
-        const std::string colliding_text = make_text(colliding);
-        const std::string spread_text = make_text(spread);
-
-        json_document with_collisions = json_document::parse(colliding_text);
-        json_document without_collisions = json_document::parse(spread_text);
-        for (const auto* pair :
-                {
-                    &colliding, &spread
-                })
-        {
-            const json_view v = (pair == &colliding ? with_collisions : without_collisions).root();
-            for (std::size_t i = 0; i < members; ++i)
-            {
-                CAPTURE(i)
-                CHECK(v[(*pair)[i]].get<std::size_t>() == i % 10);
-                CHECK(v.at((*pair)[i]).get<std::size_t>() == i % 10);
-                CHECK(v.find((*pair)[i]).key() == (*pair)[i]);
-                CHECK(!v.contains((*pair)[i] + "x"));
-            }
-            CHECK(!v.contains("missing"));
-        }
-        CHECK(with_collisions.root() == json::parse(colliding_text));
-
-        // only the object with the spread keys got a table (both texts have the
-        // same length, so the tables are the only difference)
-        with_collisions.shrink_to_fit();
-        without_collisions.shrink_to_fit();
-        CHECK(without_collisions.memory_usage() >= with_collisions.memory_usage() + (table_size * sizeof(std::uint32_t)));
-    }
-
-    SECTION("keys that differ in their last bytes are spread over the table")
-    {
-        // The hash must spread the usual families of keys (numbered names, hex
-        // strings, dates, short names): a key farther than index_max_displacement
-        // from its home slot would leave the object without a table. The keys
-        // are placed with linear probing, as the table does.
-        const auto max_displacement = [](const std::vector<std::string>& keys)
-        {
-            std::size_t slots = 16;
-            while (slots < 2 * keys.size())
-            {
-                slots *= 2;
-            }
-            std::vector<bool> used(slots, false);
-            std::size_t farthest = 0;
-            for (const std::string& key : keys)
-            {
-                std::size_t i = nlohmann::detail::conditional_static_cast<std::size_t>(nlohmann::detail::view::key_hash(key.data(), key.size())) & (slots - 1);
-                std::size_t distance = 0;
-                while (used[i])
-                {
-                    i = (i + 1) & (slots - 1);
-                    ++distance;
-                }
-                used[i] = true;
-                farthest = (std::max)(farthest, distance);
-            }
-            return farthest;
-        };
-        // the keys of a printf-like pattern with one %d, %0Nd or %0Nx, formatted with a stream
-        // (a format string that is not a literal is a Flawfinder error)
-        const auto numbered = [](const char* format, int count, int step)
-        {
-            const std::string pattern(format);
-            const std::size_t percent = pattern.find('%');
-            std::size_t conversion = percent + 1;
-            std::size_t width = 0;
-            while (pattern[conversion] >= '0' && pattern[conversion] <= '9')
-            {
-                width = (width * 10) + static_cast<std::size_t>(pattern[conversion] - '0');
-                ++conversion;
-            }
-            const bool hex = pattern[conversion] == 'x';
-            std::vector<std::string> keys;
-            for (int i = 0; i < count; ++i)
-            {
-                std::ostringstream key;
-                key << pattern.substr(0, percent) << std::setfill('0') << std::setw(static_cast<int>(width))
-                    << (hex ? std::hex : std::dec) << (i * step) << pattern.substr(conversion + 1);
-                keys.push_back(key.str());
-            }
-            return keys;
-        };
-        for (const char* format :
-                {"key%d", "%d", "item_%04d", "a%05d", "%03dxyz", "id%d", "user_%d", "%d_suffix", "0x%04x", "A%07d", "12345678%d", "1234567%d", "123456789%d",
-                 "configuration_parameter_value_%04d_extra", "2026-01-%02dT00:00:00Z"
-                })
-        {
-            CAPTURE(format)
-            CHECK(max_displacement(numbered(format, std::string(format).find("%02d") != std::string::npos ? 60 : 1000, 1)) < nlohmann::detail::view::index_max_displacement); // NOLINT(abseil-string-find-str-contains)
-            CHECK(max_displacement(numbered(format, 600, 7)) < nlohmann::detail::view::index_max_displacement);
-        }
-        std::mt19937_64 rng(7); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
-        for (const std::size_t length :
-                {
-                    std::size_t{1}, std::size_t{2}, std::size_t{3}, std::size_t{5}, std::size_t{7}, std::size_t{8}, std::size_t{9}, std::size_t{12}, std::size_t{16}, std::size_t{17}, std::size_t{33}
-                })
-        {
-            CAPTURE(length)
-            std::set<std::string> distinct;
-            // (there are 26 and 676 keys of one and two letters)
-            std::size_t wanted = 700;
-            if (length == 1)
-            {
-                wanted = 26;
-            }
-            else if (length == 2)
-            {
-                wanted = 500;
-            }
-            while (distinct.size() < wanted)
-            {
-                std::string key(length, 'a');
-                for (char& c : key)
-                {
-                    c = static_cast<char>('a' + (rng() % 26));
-                }
-                distinct.insert(key);
-            }
-            CHECK(max_displacement(std::vector<std::string>(distinct.begin(), distinct.end())) < nlohmann::detail::view::index_max_displacement);
-        }
-    }
-
-    SECTION("keys of every length that differ in one byte")
-    {
-        // In a large object, a key is found by comparing its bytes with those of the member the
-        // table points to: up to 16 bytes as two overlapping words, longer ones with memcmp.
-        // Keys of every length from 0 to 40, and keys that differ from them in one byte.
-        std::mt19937_64 rng(2026); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
-        std::vector<std::string> keys;
-        std::set<std::string> distinct;
-        for (std::size_t length = 0; length <= 40; ++length)
-        {
-            for (int copy = 0; copy < 5; ++copy)
-            {
-                std::string key(length, 'a');
-                for (char& c : key)
-                {
-                    c = static_cast<char>('a' + (rng() % 26));
-                }
-                if (distinct.insert(key).second)
-                {
-                    keys.push_back(key);
-                }
-            }
-        }
-        std::string text = "{";
-        for (std::size_t i = 0; i < keys.size(); ++i)
-        {
-            text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i);
-        }
-        text += "}";
-        REQUIRE(keys.size() >= 128); // (a table is built for 128 members)
-        const json_document d = json_document::parse(text);
-        const json_view v = d.root();
-        for (std::size_t i = 0; i < keys.size(); ++i)
-        {
-            CAPTURE(keys[i])
-            CHECK(v[keys[i]].get<std::size_t>() == i);
-            CHECK(v.at(keys[i]).get<std::size_t>() == i);
-            CHECK(v.contains(keys[i]));
-            for (std::size_t at = 0; at < keys[i].size(); ++at)
-            {
-                std::string other = keys[i];
-                other[at] = other[at] == 'z' ? 'y' : 'z';
-                CAPTURE(other)
-                CHECK(v.contains(other) == (distinct.count(other) != 0));
-            }
-            CHECK(v.contains(keys[i] + "a") == (distinct.count(keys[i] + "a") != 0));
-            if (!keys[i].empty())
-            {
-                CHECK(v.contains(keys[i].substr(1)) == (distinct.count(keys[i].substr(1)) != 0));
-            }
-        }
-    }
-
-    SECTION("shrink_to_fit releases the tables' spare capacity")
-    {
-        const auto make_text = [](int objects, int members)
-        {
-            std::string text = "[";
-            for (int object = 0; object < objects; ++object)
-            {
-                text += object != 0 ? ",{" : "{";
-                for (int i = 0, n = members + object; i < n; ++i)
-                {
-                    text += (i != 0 ? ",\"" : "\"") + std::to_string(i) + "\":" + std::to_string(i);
-                }
-                text += '}';
-            }
-            return text + "]";
-        };
-        const std::string small_text = make_text(5, 150);
-        const std::string big_text = make_text(40, 400);
-
-        // reading a big text, and then a small one, leaves the spare capacity
-        // of the big one: shrink_to_fit() brings the document to the size of
-        // one parsed from the small text alone
-        json_document d = json_document::parse(big_text);
-        const std::size_t big = d.memory_usage();
-        d.read(small_text);
-        CHECK(d.memory_usage() >= big);
-        d.shrink_to_fit();
-        json_document fresh = json_document::parse(small_text);
-        fresh.shrink_to_fit();
-        CHECK(d.memory_usage() == fresh.memory_usage());
-        CHECK(d.memory_usage() < big / 2);
-        CHECK(d.root() == json::parse(small_text));
-        for (int object = 0; object < 5; ++object)
-        {
-            const json_view v = d.root()[static_cast<std::size_t>(object)];
-            for (int i = 0, n = 150 + object; i < n; ++i)
-            {
-                CHECK(v[std::to_string(i)].get<int>() == i);
-            }
-        }
-    }
-
-    SECTION("nested, reused, and in arrays")
-    {
-        std::string inner = "{";
-        for (int i = 0; i < 300; ++i)
-        {
-            inner += (i != 0 ? ",\"m" : "\"m") + std::to_string(i) + "\":" + std::to_string(i);
-        }
-        inner += '}';
-        const std::string text = "[" + inner + ",{\"x\":" + inner + "}," + inner + "]";
-        json_document d = json_document::parse(text);
-        CHECK(d.root()[0]["m299"].get<int>() == 299);
-        CHECK(d.root()[1]["x"]["m150"].get<int>() == 150);
-        CHECK(d.root()[2]["m0"].get<int>() == 0);
-        const std::size_t with_index = d.memory_usage();
-        d.read(std::string("{\"small\": 1}"));
-        CHECK(d.root()["small"].get<int>() == 1);
-        d.read(text);
-        CHECK(d.root()[2]["m7"].get<int>() == 7);
-        CHECK(d.memory_usage() >= with_index / 2);
-    }
 }

tests/src/unit-json_view_dump_escape.cpp

@@ -0,0 +1,298 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json_view.hpp>
+using nlohmann::json;
+using nlohmann::ordered_json;
+using nlohmann::json_document;
+using nlohmann::ordered_json_editable_document;
+using nlohmann::json_view;
+using nlohmann::ordered_json_document;
+using nlohmann::ordered_json_view;
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <iomanip>
+#include <map>
+#include <random>
+#include <set>
+#include <sstream>
+#include <string>
+#include <vector>
+
+// These tests were split off unit-json_view_dump.cpp, whose object file got too large for the MinGW
+// linker (see json_view_test_helpers.hpp). Like that file, this one is also built
+// with C++17, as it mentions JSON_HAS_CPP_17.
+
+TEST_CASE("json_view dump: escaping, nesting, and output buffers")
+{
+    SECTION("members in document order, all of them")
+    {
+        const json_document d = json_document::parse(R"({"b": 1, "a": 2, "b": 3})");
+        CHECK(d.root().dump() == R"({"b":1,"a":2,"b":3})");
+        CHECK(d.root().dump(1) == "{\n \"b\": 1,\n \"a\": 2,\n \"b\": 3\n}");
+        // dump() writes all members, though the lookup finds the first
+        CHECK(d.root()["b"].dump() == "1");
+    }
+
+    SECTION("deep nesting")
+    {
+        const std::string deep = std::string(100000, '[') + std::string(100000, ']');
+        const json_document deep_document = json_document::parse(deep);
+        CHECK(deep_document.root().dump() == deep);
+    }
+
+    SECTION("ensure_ascii: a character that needs an escape at each position of a string")
+    {
+        // string lengths around the width of the vector steps, in a string value, a key, and a value near the end of the text
+        for (const char* const special :
+                {
+                    "\xC3\xA9", "\xE4\xB8\xAD", "\xF0\x9F\x98\x80", "\x7F", "\\n", "\\u0001", "\\\"", "\\\\"
+                })
+        {
+            for (std::size_t length = 0; length <= 40; ++length)
+            {
+                for (std::size_t position = 0; position <= length; ++position)
+                {
+                    std::string content(length, 'a');
+                    content.insert(position, special);
+                    const std::array<std::string, 3> texts =
+                    {
+                        {
+                            "\"" + content + "\"",
+                            "[\"" + content + "\"]",
+                            "{\"" + content + "\":1}",
+                        }
+                    };
+                    for (const std::string& text : texts)
+                    {
+                        CAPTURE(text)
+                        const ordered_json_document d = ordered_json_document::parse(text);
+                        const ordered_json j = ordered_json::parse(text);
+                        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+                        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
+                        CHECK(d.root().dump() == j.dump());
+                    }
+                }
+            }
+        }
+    }
+
+    SECTION("ensure_ascii: every character of the Basic Multilingual Plane and some beyond")
+    {
+        // (the two- and three-byte sequences, including the ranges that need a check: E0, ED, EF BF BF)
+        std::string text = "[";
+        std::size_t in_chunk = 0;
+        const auto append = [&](std::uint32_t cp)
+        {
+            if (cp < 0x80)
+            {
+                if (cp < 0x20 || cp == '"' || cp == '\\')
+                {
+                    return;
+                }
+                text += static_cast<char>(cp);
+            }
+            else if (cp < 0x800)
+            {
+                text += static_cast<char>(0xC0 | (cp >> 6));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+            else if (cp < 0x10000)
+            {
+                text += static_cast<char>(0xE0 | (cp >> 12));
+                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+            else
+            {
+                text += static_cast<char>(0xF0 | (cp >> 18));
+                text += static_cast<char>(0x80 | ((cp >> 12) & 0x3F));
+                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+        };
+        for (std::uint32_t cp = 0x20; cp < 0x10400; ++cp)
+        {
+            if (cp >= 0xD800 && cp < 0xE000)
+            {
+                continue;
+            }
+            if (in_chunk == 0)
+            {
+                text += text.size() > 1 ? ",\"" : "\"";
+            }
+            append(cp);
+            if (++in_chunk == 37)
+            {
+                text += "\"";
+                in_chunk = 0;
+            }
+        }
+        text += in_chunk != 0 ? "\"]" : "]";
+        const ordered_json_document d = ordered_json_document::parse(text);
+        const ordered_json j = ordered_json::parse(text);
+        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
+        CHECK(d.root().dump() == j.dump());
+        CHECK(d.root().dump(2) == j.dump(2));
+    }
+
+    SECTION("deep nesting, indented")
+    {
+        // indentations of up to and beyond the width of the writer's fixed-size copy
+        for (const int depth :
+                {
+                    1, 5, 20, 70, 300
+                })
+        {
+            std::string text;
+            for (int i = 0; i < depth; ++i)
+            {
+                text += i % 2 == 0 ? "[1," : R"({"k":2,"\u00e9":)";
+            }
+            text += "[]";
+            for (int i = depth - 1; i >= 0; --i)
+            {
+                text += i % 2 == 0 ? "]" : "}";
+            }
+            const ordered_json_document d = ordered_json_document::parse(text);
+            const ordered_json j = ordered_json::parse(text);
+            for (const int indent :
+                    {
+                        0, 1, 2, 3, 8
+                    })
+            {
+                CHECK(d.root().dump(indent) == j.dump(indent));
+                CHECK(d.root().dump(indent, '\t') == j.dump(indent, '\t'));
+            }
+        }
+    }
+
+    SECTION("the output buffer of a small value is small")
+    {
+        // an escaped key after the value: its node lies in the arena, so the
+        // source extent of the value cannot be read from the next node
+        const std::string big(100000, 'a');
+        const std::string text = R"({"small":1,"list":[1,2,3],"k\n":")" + big + R"("})";
+        const json_document d = json_document::parse(text);
+        const auto small = d.root()["small"].dump();
+        CHECK(small == "1");
+        CHECK(small.capacity() < 4096);
+        const auto list = d.root()["list"].dump();
+        CHECK(list == "[1,2,3]");
+        CHECK(list.capacity() < 4096);
+        CHECK(d.root()["list"].dump(2).capacity() < 4096);
+
+        // the whole document and the large value are unaffected
+        CHECK(d.root().dump() == ordered_json::parse(text).dump());
+        CHECK(d.root()["k\n"].dump() == "\"" + big + "\"");
+    }
+
+    SECTION("output that outgrows the estimate")
+    {
+        // ensure_ascii writes six bytes for each two-byte character
+        std::string chars;
+        for (int i = 0; i < 5000; ++i)
+        {
+            chars += "\xC3\xA9";
+        }
+        const json_document d = json_document::parse(R"({"a":")" + chars + R"(","k\n":1})");
+        const json expected = json::parse("\"" + chars + "\"");
+        CHECK(d.root()["a"].dump(-1, ' ', true) == expected.dump(-1, ' ', true));
+        CHECK(d.root()["a"].dump(-1, ' ', true).size() == 2 + (5000 * 6));
+    }
+
+    SECTION("ensure_ascii with strings of the source, decoded strings, and edited strings")
+    {
+        // plain ASCII, non-ASCII, escaped (decoded), and mixed strings, as values and as keys;
+        // the second text has a DEL, which ensure_ascii writes as an escape
+        for (const char* const del :
+                {"", "\x7F"
+                })
+        {
+            const std::string text = std::string("{\"plain\":\"abc\",\"caf\xC3\xA9\":\"\xC3\xA9\xE2\x82\xAC\xF0\x9F\x98\x80\",")
+                                     + "\"esc\\n\\\"\":\"a\\tb\\u00e4\\ud83d\\ude00\",\"del\":\"a" + del + "b\",\"\":\"\"," // NOLINT(modernize-raw-string-literal)
+                                     + "\"list\":[\"x\",\"\xC3\xBC\",\"\\\\\",\"long ASCII string with more than thirty-two bytes in it\","
+                                     + "\"long string with more than thirty-two bytes and one non-ASCII byte \xC3\xB6\"],"
+                                     + "\"n\":[1,2.5,-0,true,null]}";
+            const ordered_json j = ordered_json::parse(text);
+            const ordered_json_document d = ordered_json_document::parse(text);
+            CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+            CHECK(d.root().dump(4, ' ', true) == j.dump(4, ' ', true));
+            CHECK(d.root().dump() == j.dump());
+            CHECK(d.root()["list"].dump(-1, ' ', true) == j["list"].dump(-1, ' ', true));
+            CHECK(d.root()["del"].dump(-1, ' ', true) == j["del"].dump(-1, ' ', true));
+
+            // strings that an edit wrote (the source strings that they replace were plain)
+            ordered_json_editable_document e = ordered_json_editable_document::parse(text);
+            ordered_json k = j;
+            e.set(e.root()["plain"], std::string("\xC3\xA4gypten"));
+            k["plain"] = "\xC3\xA4gypten";
+            e.set(e.root()["list"][0], std::string("ascii after edit"));
+            k["list"][0] = "ascii after edit";
+            e.set(e.root()["list"][1], std::string("\xC3\xA4"));
+            k["list"][1] = "\xC3\xA4";
+            e.set(e.root()["del"], std::string("tab\there"));
+            k["del"] = "tab\there";
+            CHECK(e.root().dump(-1, ' ', true) == k.dump(-1, ' ', true));
+            CHECK(e.root().dump(2, ' ', true) == k.dump(2, ' ', true));
+            CHECK(e.root().dump() == k.dump());
+
+            // strings that were edited from or to ASCII text
+            e.set(e.root()["list"][2], std::string("\xC3\xA4"));
+            k["list"][2] = "\xC3\xA4";
+            e.set(e.root()["list"][4], std::string("plain again"));
+            k["list"][4] = "plain again";
+            CHECK(e.root().dump(-1, ' ', true) == k.dump(-1, ' ', true));
+        }
+    }
+
+    SECTION("ensure_ascii with DEL or a non-ASCII character at every position")
+    {
+        // the check whether a string of the source has no byte >= 0x7F reads
+        // eight bytes at a time and then the rest one by one
+        for (std::size_t length = 1; length <= 20; ++length)
+        {
+            for (std::size_t pos = 0; pos < length; ++pos)
+            {
+                for (const char* const c :
+                        {
+                            "\x7F", "\x7E", "\xC3\xA4", "\xC3\xBF" // NOLINT(modernize-raw-string-literal)
+                        })
+                {
+                    const std::string s = std::string(pos, 'a') + c + std::string(length - pos - 1, 'b');
+                    std::string text = "[\"";
+                    text.append(s).append("\",{\"").append(s).append("\":1}]");
+                    const json_document d = json_document::parse(text);
+                    const json j = json::parse(text);
+                    CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+                    CHECK(d.root().dump(1, ' ', true) == j.dump(1, ' ', true));
+                }
+            }
+        }
+    }
+
+    SECTION("streams and discarded views")
+    {
+        const json_document d = json_document::parse(R"({"a": [1, 2]})");
+        std::ostringstream compact;
+        compact << d.root();
+        CHECK(compact.str() == R"({"a":[1,2]})");
+        std::ostringstream pretty;
+        pretty << std::setw(2) << std::setfill('.') << d.root() << d.root()["a"];
+        CHECK(pretty.str() == "{\n..\"a\": [\n....1,\n....2\n..]\n}[1,2]");
+        CHECK(json_view().dump() == json(json::value_t::discarded).dump());
+    }
+}

tests/src/unit-json_view_edit.cpp

@@ -532,18 +532,18 @@ TEST_CASE("json_view edits: errors")
 
     CHECK_THROWS_WITH_AS(d.set(other_editable.root(), 1), "[json.exception.invalid_iterator.202] view does not belong to this document", json::invalid_iterator&);
     CHECK_THROWS_WITH_AS(d.set(json_editable_view(), 1), "[json.exception.invalid_iterator.202] view does not belong to this document", json::invalid_iterator&);
-    CHECK_THROWS_WITH_AS(d.set(root["a"], "k", 1), "[json.exception.type_error.305] cannot use operator[] with a string argument with array", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.set(root["a"], "k", 1), json_view_test::message("type_error.305", "/a", 21, 27, "cannot use operator[] with a string argument with array").c_str(), json::type_error&);
-    CHECK_THROWS_WITH_AS(d.set(root["o"], 0, 1), "[json.exception.type_error.305] cannot use operator[] with a numeric argument with object", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.set(root["o"], 0, 1), json_view_test::message("type_error.305", "/o", 6, 14, "cannot use operator[] with a numeric argument with object").c_str(), json::type_error&);
-    CHECK_THROWS_WITH_AS(d.set(root["a"], 2, 1), "[json.exception.out_of_range.401] array index 2 is out of range", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.set(root["a"], 2, 1), json_view_test::message("out_of_range.401", "/a", 21, 27, "array index 2 is out of range").c_str(), json::out_of_range&);
-    CHECK_THROWS_WITH_AS(d.set(root["a"], -1, 1), "[json.exception.out_of_range.401] array index -1 is out of range", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.set(root["a"], -1, 1), json_view_test::message("out_of_range.401", "/a", 21, 27, "array index -1 is out of range").c_str(), json::out_of_range&);
-    CHECK_THROWS_WITH_AS(d.push_back(root["o"], 1), "[json.exception.type_error.308] cannot use push_back() with object", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.push_back(root["o"], 1), json_view_test::message("type_error.308", "/o", 6, 14, "cannot use push_back() with object").c_str(), json::type_error&);
-    CHECK_THROWS_WITH_AS(d.insert(root["n"], 0, 1), "[json.exception.type_error.309] cannot use insert() with number", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.insert(root["n"], 0, 1), json_view_test::message("type_error.309", "/n", 34, 35, "cannot use insert() with number").c_str(), json::type_error&);
-    CHECK_THROWS_WITH_AS(d.insert(root["a"], 3, 1), "[json.exception.out_of_range.401] array index 3 is out of range", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.insert(root["a"], 3, 1), json_view_test::message("out_of_range.401", "/a", 21, 27, "array index 3 is out of range").c_str(), json::out_of_range&);
-    CHECK_THROWS_WITH_AS(d.erase(root["n"], "k"), "[json.exception.type_error.307] cannot use erase() with number", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.erase(root["n"], "k"), json_view_test::message("type_error.307", "/n", 34, 35, "cannot use erase() with number").c_str(), json::type_error&);
-    CHECK_THROWS_WITH_AS(d.erase(root["o"], 0), "[json.exception.type_error.307] cannot use erase() with object", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.erase(root["o"], 0), json_view_test::message("type_error.307", "/o", 6, 14, "cannot use erase() with object").c_str(), json::type_error&);
-    CHECK_THROWS_WITH_AS(d.erase(root["a"], 2), "[json.exception.out_of_range.401] array index 2 is out of range", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.erase(root["a"], 2), json_view_test::message("out_of_range.401", "/a", 21, 27, "array index 2 is out of range").c_str(), json::out_of_range&);
     CHECK_THROWS_WITH_AS(d.erase(json::json_pointer("")), "[json.exception.out_of_range.405] JSON pointer has no parent", json::out_of_range&);
-    CHECK_THROWS_WITH_AS(d.erase(json::json_pointer("/missing/x")), "[json.exception.out_of_range.403] key 'missing' not found", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.erase(json::json_pointer("/missing/x")), json_view_test::message("out_of_range.403", "", 0, 47, "key 'missing' not found").c_str(), json::out_of_range&);
     CHECK_THROWS_WITH_AS(d.set(json::json_pointer("/a/01"), 1), "[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'", json::parse_error&);
     CHECK_THROWS_WITH_AS(d.set(root, json_editable_view()), "[json.exception.type_error.302] type must be a value, but is discarded", json::type_error&);
     CHECK_THROWS_WITH_AS(d.set(root, json::binary({1, 2})), "[json.exception.type_error.319] cannot store a binary value in a json_document", json::type_error&);

tests/src/unit-json_view_from_json.cpp

@@ -39,6 +39,7 @@ using nlohmann::ordered_json_document;
 
 #ifdef JSON_HAS_CPP_17
     #include <optional>
+    #include <string_view>
 #endif
 
 // NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair; same() compares floating-point values on purpose
@@ -337,8 +338,7 @@ TEST_CASE("json_view from_json")
         CHECK(d.root().get<std::unordered_map<std::string, int>>().at("a") == 3);
     }
 
-    // (the exceptions of views have neither the path nor the byte range of the value)
+#if !defined(JSON_NOEXCEPTION)
-#if !defined(JSON_NOEXCEPTION) && !JSON_DIAGNOSTICS && !JSON_DIAGNOSTIC_POSITIONS
     SECTION("std types: the same errors as from the materialized value")
     {
         const json_document d = json_document::parse(R"([[1, "x"], {"a": 1}, "text", [1], 5, null])");
@@ -403,10 +403,10 @@ TEST_CASE("json_view from_json")
         CHECK(d.root()[4].get<strict_color>() == strict_color::red);
 #if !defined(JSON_NOEXCEPTION)
         const json j = d.root().materialize();
-        CHECK(exception_of_call([&] { static_cast<void>(d.root()[2].get<strict_color>()); }) == "[json.exception.out_of_range.410] enum value out of range for strict_color: \"purple\"");
 #if !JSON_DIAGNOSTICS && !JSON_DIAGNOSTIC_POSITIONS
-        CHECK(exception_of_call([&] { static_cast<void>(d.root()[2].get<strict_color>()); }) == exception_of_call([&] { static_cast<void>(j[2].get<strict_color>()); }));
+        CHECK(exception_of_call([&] { static_cast<void>(d.root()[2].get<strict_color>()); }) == "[json.exception.out_of_range.410] enum value out of range for strict_color: \"purple\"");
 #endif
+        CHECK(exception_of_call([&] { static_cast<void>(d.root()[2].get<strict_color>()); }) == exception_of_call([&] { static_cast<void>(j[2].get<strict_color>()); }));
 #endif
     }
 
@@ -443,6 +443,30 @@ TEST_CASE("json_view from_json")
         CHECK(d.root().materialize().get<point>().x == 3);
     }
 
+    SECTION("escaped keys: members are found by their decoded names")
+    {
+        // keys are decoded before they are compared, as by parse(); a lookup
+        // that compares the raw bytes of the source would miss these members
+        const json_document d = json_document::parse(R"([{"\u0078": 1, "y": 2}, {"V\u0061lue": 3, "Te\u0078t": "t"}, {"\u0062": "escaped"}, {"x": 1, "\u0078": 3, "y": 2}])");
+        const json j = d.root().materialize();
+        CHECK(d.root()[0].get<point>().x == 1);
+        CHECK(d.root()[0].get<point>().y == 2);
+        CHECK((d.root()[0].get<point>() == j[0].get<point>()));
+        CHECK(d.root()[1].get<with_names>().value == 3);
+        CHECK(d.root()[1].get<with_names>().text == "t");
+        CHECK(d.root()[2].get<with_defaults>().b == "escaped");
+        CHECK(d.root()[2].get<with_defaults>().a == 1);
+        // a duplicate key written once plain and once escaped: still the first member
+        CHECK(d.root()[3].get<point>().x == 1);
+        CHECK(j[3].get<point>().x == 3);
+#if !defined(JSON_NOEXCEPTION) && !JSON_DIAGNOSTICS && !JSON_DIAGNOSTIC_POSITIONS
+        // an escaped backslash is part of the decoded key: "x\\" is not "x"
+        const json_document e = json_document::parse(R"({"x\\": 1, "y": 2})");
+        CHECK(exception_of_call([&] { static_cast<void>(e.root().get<point>()); }) == exception_of_call([&] { static_cast<void>(e.root().materialize().get<point>()); }));
+        CHECK(exception_of_call([&] { static_cast<void>(e.root().get<point>()); }) == "[json.exception.out_of_range.403] key 'x' not found");
+#endif
+    }
+
     SECTION("editable documents and ordered_json")
     {
         json_editable_document e = json_editable_document::parse(R"({"x": 1, "y": 2})");
@@ -452,11 +476,9 @@ TEST_CASE("json_view from_json")
         CHECK(o.root().get<shape>().center.y == 2);
     }
 
-#if !defined(JSON_NOEXCEPTION) && !JSON_DIAGNOSTICS && !JSON_DIAGNOSTIC_POSITIONS
+#if !defined(JSON_NOEXCEPTION)
     SECTION("errors are those of the same conversion of a json value")
     {
-        // (with JSON_DIAGNOSTICS, those of json name the path of the value,
-        // and with JSON_DIAGNOSTIC_POSITIONS its bytes)
         const json_document d = json_document::parse(R"([{"x": 1}, {"x": "1", "y": 2}, [1, 2], {"id": "7", "c": "red"}])");
         const json j = d.root().materialize();
         for (std::size_t i = 0; i < 3; ++i)
@@ -469,5 +491,70 @@ TEST_CASE("json_view from_json")
 #endif
 }
 
+#ifdef JSON_HAS_CPP_17
+namespace view_from_json
+{
+// a string_view member is not copied: it points into the source text or, for a
+// string with escape sequences, into the buffer of decoded strings of the document
+struct named_view
+{
+    // initialized for GCC -Weffc++
+    // NOLINTNEXTLINE(readability-redundant-member-init)
+    std::string_view name{};
+    int n = 0;
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(named_view, name, n)
+};
+}  // namespace view_from_json
+
+TEST_CASE("json_view from_json: string_view members borrow from the document")
+{
+    using view_from_json::named_view;
+
+    // whether all of s is inside the bytes of text
+    const auto within = [](std::string_view s, std::string_view text)
+    {
+        const auto first = reinterpret_cast<std::uintptr_t>(text.data());
+        const auto begin = reinterpret_cast<std::uintptr_t>(s.data());
+        return begin >= first && begin + s.size() <= first + text.size();
+    };
+
+    SECTION("a string without escapes points into the source text")
+    {
+        const std::string text = R"({"name": "hello", "n": 1})";
+        const json_document d = json_document::parse(text);
+        REQUIRE_FALSE(d.owns_source());
+        const auto r = d.root().get<named_view>();
+        CHECK(r.name == "hello");
+        CHECK(r.n == 1);
+        CHECK(within(r.name, text));
+        CHECK(within(r.name, d.source()));
+    }
+
+    SECTION("a string with escapes points into the document, not into the source text")
+    {
+        const std::string text = R"({"name": "a\nb", "n": 2})";
+        json_document d = json_document::parse(text);
+        REQUIRE_FALSE(d.owns_source());
+        const auto r = d.root().get<named_view>();
+        CHECK(r.name == "a\nb");
+        CHECK(r.n == 2);
+        CHECK_FALSE(within(r.name, text));
+        // valid as long as the document is alive, even if the document is moved
+        const json_document moved = std::move(d);
+        CHECK(r.name == "a\nb");
+        CHECK(moved.root().get<named_view>().name == r.name);
+    }
+
+    SECTION("a document that owns its text keeps the members readable while it is alive")
+    {
+        const json_document d = json_document::parse(std::string(R"({"name": "owned", "n": 3})"));
+        REQUIRE(d.owns_source());
+        const auto r = d.root().get<named_view>();
+        CHECK(r.name == "owned");
+        CHECK(within(r.name, d.source()));
+    }
+}
+#endif
+
 DOCTEST_CLANG_SUPPRESS_WARNING_POP
 DOCTEST_GCC_SUPPRESS_WARNING_POP

tests/src/unit-json_view_large.cpp

@@ -0,0 +1,544 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json_view.hpp>
+using nlohmann::json;
+using nlohmann::ordered_json;
+using nlohmann::json_document;
+using nlohmann::ordered_json_editable_document;
+using nlohmann::json_view;
+using nlohmann::ordered_json_document;
+using nlohmann::ordered_json_view;
+
+#include "json_view_test_helpers.hpp"
+using json_view_test::generator;
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <iomanip>
+#include <map>
+#include <random>
+#include <set>
+#include <sstream>
+#include <string>
+#include <vector>
+
+// These tests were split off unit-json_view_dump.cpp, whose object file got too large for the MinGW
+// linker (see json_view_test_helpers.hpp). Like that file, this one is also built
+// with C++17, as it mentions JSON_HAS_CPP_17.
+
+TEST_CASE("json_view comparison")
+{
+    SECTION("equality of the values parse() produces")
+    {
+        generator g;
+        std::vector<std::string> texts;
+        for (int i = 0; i < 600; ++i)
+        {
+            std::string text;
+            g.value(text, 0);
+            texts.push_back(text);
+            // the same value written differently: sorted keys, canonical numbers
+            texts.push_back(json::parse(text).dump(1));
+        }
+        for (std::size_t i = 0; i + 2 < texts.size(); ++i)
+        {
+            for (std::size_t k = i; k < i + 3; ++k)
+            {
+                CAPTURE(texts[i])
+                CAPTURE(texts[k])
+                const json_document a = json_document::parse(texts[i]);
+                const json_document b = json_document::parse(texts[k]);
+                const json ja = json::parse(texts[i]);
+                const json jb = json::parse(texts[k]);
+                CHECK((a.root() == b.root()) == (ja == jb));
+                CHECK((a.root() != b.root()) == (ja != jb));
+                CHECK((a.root() == jb) == (ja == jb));
+                CHECK((jb == a.root()) == (ja == jb));
+                CHECK((a.root() != jb) == (ja != jb));
+                CHECK((jb != a.root()) == (ja != jb));
+
+                // ordered_json compares members in order
+                const ordered_json_document oa = ordered_json_document::parse(texts[i]);
+                const ordered_json_document ob = ordered_json_document::parse(texts[k]);
+                const ordered_json oja = ordered_json::parse(texts[i]);
+                const ordered_json ojb = ordered_json::parse(texts[k]);
+                CHECK((oa.root() == ob.root()) == (oja == ojb));
+                CHECK((oa.root() == ojb) == (oja == ojb));
+            }
+        }
+    }
+
+    SECTION("numbers, duplicate keys, member order")
+    {
+        const auto same = [](const char* x, const char* y)
+        {
+            const json_document dx = json_document::parse(x);
+            const json_document dy = json_document::parse(y);
+            return dx.root() == dy.root();
+        };
+        CHECK(same("1", "1.0"));
+        CHECK(same("[1, -1, 2.5]", "[1.0, -1.0, 25e-1]"));
+        CHECK(!same("1", "1.5"));
+        CHECK(same("18446744073709551615", "18446744073709551615"));
+        CHECK(same(R"({"a": 1, "a": 2})", R"({"a": 2})"));
+        CHECK(!same(R"({"a": 1, "a": 2})", R"({"a": 1})"));
+        CHECK(same(R"({"a": 1, "b": 2})", R"({"b": 2, "a": 1})"));
+        CHECK(!same(R"({"a": 1})", R"({"a": 1, "b": 2})"));
+        CHECK(!same("[1, 2]", "[2, 1]"));
+        CHECK(!same("\"a\"", "\"b\""));
+        CHECK(same("\"\\u00e9\"", "\"\xc3\xa9\""));
+        CHECK(!same("null", "false"));
+        CHECK(!same("[]", "{}"));
+        const ordered_json_document dup = ordered_json_document::parse(R"({"a": 1, "b": 2, "a": 3})");
+        const ordered_json_document last = ordered_json_document::parse(R"({"a": 3, "b": 2})");
+        CHECK(dup.root() == last.root());
+        // (== compares as parse() resolves duplicates, a lookup finds the first)
+        CHECK(dup.root()["a"].materialize() == 1);
+        CHECK(dup.root()["a"] != last.root()["a"]);
+        const ordered_json_document ab = ordered_json_document::parse(R"({"a": 1, "b": 2})");
+        const ordered_json_document ba = ordered_json_document::parse(R"({"b": 2, "a": 1})");
+        CHECK(ab.root() != ba.root());
+
+        // discarded values compare as basic_json's do
+        const json discarded(json::value_t::discarded);
+        CHECK((json_view() == json_view()) == (discarded == discarded)); // NOLINT(readability-container-size-empty): operator== is tested
+        CHECK((json_view() == discarded) == (discarded == discarded)); // NOLINT(readability-container-size-empty)
+        const json_document null_document = json_document::parse("null");
+        CHECK(!(json_view() == null_document.root())); // NOLINT(readability-container-size-empty)
+        CHECK(!(null_document.root() == discarded));
+    }
+
+    SECTION("deep nesting")
+    {
+        const std::string deep = std::string(100000, '[') + std::string(100000, ']');
+        const json_document a = json_document::parse(deep);
+        const json_document b = json_document::parse(deep);
+        CHECK(a.root() == b.root());
+        CHECK(a.root() == json::parse(deep));
+        const std::string other = std::string(100000, '[') + "1" + std::string(100000, ']');
+        const json_document c = json_document::parse(other);
+        CHECK(a.root() != c.root());
+    }
+}
+
+TEST_CASE("json_view large objects")
+{
+    // objects with 128 members or more are looked up with a hash index
+    for (const std::size_t members :
+            {
+                127u, 128u, 129u, 10000u
+            })
+    {
+        CAPTURE(members)
+        std::string text = "{";
+        for (std::size_t i = 0; i < members; ++i)
+        {
+            text += (i != 0 ? ",\"" : "\"") + std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\\n" : "") + "\":" + std::to_string(i);
+        }
+        text += R"(,"":"empty key","k1":"a duplicate of an earlier key"})";
+        const json_document d = json_document::parse(text);
+        const json_view v = d.root();
+        const json j = json::parse(text);
+        for (std::size_t i = 0; i < members; ++i)
+        {
+            const std::string key = std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\n" : "");
+            CHECK(v[key].get<std::size_t>() == i);
+            CHECK(v.contains(key));
+            CHECK(v.find(key).key() == key);
+            CHECK(v.at(key).get<std::size_t>() == i);
+            CHECK(!v.contains(key + "x"));
+        }
+        CHECK(v[""].get_string() == "empty key");
+        CHECK(v["k1"].get<int>() == 1); // the first of duplicate keys, as for small objects
+        CHECK(!v.contains("missing"));
+        CHECK_THROWS_WITH_AS(v.at("missing"), json_view_test::message("out_of_range.403", "", 0, text.size(), "key 'missing' not found").c_str(), json::out_of_range&);
+        CHECK(v == j);
+        CHECK(v.materialize() == j);
+    }
+
+    SECTION("duplicate keys: the first member wins, with and without a table")
+    {
+        // an object of `total` members: the keys "k0".."k<n-1>" in order, then
+        // three keys repeated twice more (one copy in the middle, one at the
+        // end), and two keys repeated once; the value of a member is its
+        // position, so that the first member of a key can be told apart
+        struct member
+        {
+            std::string key;
+            std::size_t position;
+        };
+        const auto make_members = [](std::size_t total)
+        {
+            std::vector<std::string> keys;
+            for (std::size_t i = 0; i + 8 < total; ++i)
+            {
+                keys.push_back("k" + std::to_string(i));
+            }
+            const std::size_t n = keys.size();
+            const std::array<std::size_t, 3> triple = {{3, 17, n - 1}};
+            const std::array<std::size_t, 2> twice = {{5, n / 2}};
+            std::vector<std::string> ordered = keys;
+            for (const std::size_t i : triple)
+            {
+                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 2), keys[i]);
+            }
+            for (const std::size_t i : twice)
+            {
+                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 3), keys[i]);
+            }
+            for (const std::size_t i : triple)
+            {
+                ordered.push_back(keys[i]);
+            }
+            std::vector<member> result;
+            result.reserve(ordered.size());
+            for (std::size_t i = 0; i < ordered.size(); ++i)
+            {
+                result.push_back({ordered[i], i});
+            }
+            return result;
+        };
+
+        // 100 and 127 members: no table; 128 members and more: a table
+        for (const std::size_t total :
+                {
+                    100u, 127u, 128u, 200u, 5000u
+                })
+        {
+            CAPTURE(total)
+            const std::vector<member> members = make_members(total);
+            REQUIRE(members.size() >= total);
+            REQUIRE(members.size() >= 100);
+            std::string text = "{";
+            std::map<std::string, std::size_t> first;
+            std::map<std::string, std::size_t> last;
+            std::map<std::string, std::size_t> occurrences;
+            for (const member& m : members)
+            {
+                text += (text.size() > 1 ? ",\"" : "\"") + m.key + "\":" + std::to_string(m.position);
+                first.insert({m.key, m.position});
+                last[m.key] = m.position;
+                ++occurrences[m.key];
+            }
+            text += '}';
+            REQUIRE(first.size() < members.size());
+
+            const json_document d = json_document::parse(text);
+            const json_view v = d.root();
+            const json j = json::parse(text);
+            CHECK(v.size() == members.size()); // every occurrence is visited
+            const json m = v.materialize();
+            for (const auto& entry : first)
+            {
+                CAPTURE(entry.first)
+                const std::size_t expected = entry.second;
+                CHECK(v[entry.first].get<std::size_t>() == expected);
+                CHECK(v.at(entry.first).get<std::size_t>() == expected);
+                CHECK(v.find(entry.first).value().get<std::size_t>() == expected);
+                CHECK(v.value(entry.first, std::size_t{0}) == expected);
+                CHECK(v.contains(entry.first));
+                CHECK(v.count(entry.first) == occurrences[entry.first]);
+                const std::string pointer = "/" + entry.first;
+                CHECK(v[json::json_pointer(pointer)].get<std::size_t>() == expected);
+                CHECK(v.at(json::json_pointer(pointer)).get<std::size_t>() == expected);
+                CHECK(v.value(json::json_pointer(pointer), std::size_t{0}) == expected);
+                CHECK(v.contains(json::json_pointer(pointer)));
+                // materialize() and parse() keep the last value instead
+                CHECK(j[entry.first].get<std::size_t>() == last.at(entry.first));
+                CHECK(m[entry.first].get<std::size_t>() == last.at(entry.first));
+            }
+            CHECK(!v.contains("k"));
+            CHECK(v["missing"].is_discarded());
+            CHECK(v.materialize() == j);
+            CHECK(v == j);
+        }
+    }
+
+    SECTION("colliding keys")
+    {
+        // the hash is not seeded, so keys that all land in one place must not
+        // make the table build quadratic: such an object gets no table and is
+        // searched linearly
+        constexpr std::size_t members = 300;
+        constexpr std::size_t table_size = 1024; // the table size for 300 members: the next power of two >= 600
+        std::vector<std::string> colliding;
+        std::vector<std::string> spread;
+        for (std::uint64_t counter = 0; colliding.size() < members || spread.size() < members; ++counter)
+        {
+            std::string key(8, 'a');
+            std::uint64_t x = counter;
+            for (std::size_t i = 0; i < 8; ++i, x /= 26)
+            {
+                key[i] = static_cast<char>('a' + (x % 26));
+            }
+            const bool lands_in_slot_zero = (nlohmann::detail::view::key_hash(key.data(), key.size()) & (table_size - 1)) == 0;
+            if (lands_in_slot_zero && colliding.size() < members)
+            {
+                colliding.push_back(key);
+            }
+            else if (!lands_in_slot_zero && spread.size() < members)
+            {
+                spread.push_back(key);
+            }
+        }
+
+        const auto make_text = [](const std::vector<std::string>& keys)
+        {
+            std::string text = "{";
+            for (std::size_t i = 0; i < keys.size(); ++i)
+            {
+                text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i % 10);
+            }
+            return text + "}";
+        };
+        const std::string colliding_text = make_text(colliding);
+        const std::string spread_text = make_text(spread);
+
+        json_document with_collisions = json_document::parse(colliding_text);
+        json_document without_collisions = json_document::parse(spread_text);
+        for (const auto* pair :
+                {
+                    &colliding, &spread
+                })
+        {
+            const json_view v = (pair == &colliding ? with_collisions : without_collisions).root();
+            for (std::size_t i = 0; i < members; ++i)
+            {
+                CAPTURE(i)
+                CHECK(v[(*pair)[i]].get<std::size_t>() == i % 10);
+                CHECK(v.at((*pair)[i]).get<std::size_t>() == i % 10);
+                CHECK(v.find((*pair)[i]).key() == (*pair)[i]);
+                CHECK(!v.contains((*pair)[i] + "x"));
+            }
+            CHECK(!v.contains("missing"));
+        }
+        CHECK(with_collisions.root() == json::parse(colliding_text));
+
+        // only the object with the spread keys got a table (both texts have the
+        // same length, so the tables are the only difference)
+        with_collisions.shrink_to_fit();
+        without_collisions.shrink_to_fit();
+        CHECK(without_collisions.memory_usage() >= with_collisions.memory_usage() + (table_size * sizeof(std::uint32_t)));
+    }
+
+    SECTION("keys that differ in their last bytes are spread over the table")
+    {
+        // The hash must spread the usual families of keys (numbered names, hex
+        // strings, dates, short names): a key farther than index_max_displacement
+        // from its home slot would leave the object without a table. The keys
+        // are placed with linear probing, as the table does.
+        const auto max_displacement = [](const std::vector<std::string>& keys)
+        {
+            std::size_t slots = 16;
+            while (slots < 2 * keys.size())
+            {
+                slots *= 2;
+            }
+            std::vector<bool> used(slots, false);
+            std::size_t farthest = 0;
+            for (const std::string& key : keys)
+            {
+                std::size_t i = nlohmann::detail::conditional_static_cast<std::size_t>(nlohmann::detail::view::key_hash(key.data(), key.size())) & (slots - 1);
+                std::size_t distance = 0;
+                while (used[i])
+                {
+                    i = (i + 1) & (slots - 1);
+                    ++distance;
+                }
+                used[i] = true;
+                farthest = (std::max)(farthest, distance);
+            }
+            return farthest;
+        };
+        // the keys of a printf-like pattern with one %d, %0Nd or %0Nx, formatted with a stream
+        // (a format string that is not a literal is a Flawfinder error)
+        const auto numbered = [](const char* format, int count, int step)
+        {
+            const std::string pattern(format);
+            const std::size_t percent = pattern.find('%');
+            std::size_t conversion = percent + 1;
+            std::size_t width = 0;
+            while (pattern[conversion] >= '0' && pattern[conversion] <= '9')
+            {
+                width = (width * 10) + static_cast<std::size_t>(pattern[conversion] - '0');
+                ++conversion;
+            }
+            const bool hex = pattern[conversion] == 'x';
+            std::vector<std::string> keys;
+            for (int i = 0; i < count; ++i)
+            {
+                std::ostringstream key;
+                key << pattern.substr(0, percent) << std::setfill('0') << std::setw(static_cast<int>(width))
+                    << (hex ? std::hex : std::dec) << (i * step) << pattern.substr(conversion + 1);
+                keys.push_back(key.str());
+            }
+            return keys;
+        };
+        for (const char* format :
+                {"key%d", "%d", "item_%04d", "a%05d", "%03dxyz", "id%d", "user_%d", "%d_suffix", "0x%04x", "A%07d", "12345678%d", "1234567%d", "123456789%d",
+                 "configuration_parameter_value_%04d_extra", "2026-01-%02dT00:00:00Z"
+                })
+        {
+            CAPTURE(format)
+            CHECK(max_displacement(numbered(format, std::string(format).find("%02d") != std::string::npos ? 60 : 1000, 1)) < nlohmann::detail::view::index_max_displacement); // NOLINT(abseil-string-find-str-contains)
+            CHECK(max_displacement(numbered(format, 600, 7)) < nlohmann::detail::view::index_max_displacement);
+        }
+        std::mt19937_64 rng(7); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+        for (const std::size_t length :
+                {
+                    std::size_t{1}, std::size_t{2}, std::size_t{3}, std::size_t{5}, std::size_t{7}, std::size_t{8}, std::size_t{9}, std::size_t{12}, std::size_t{16}, std::size_t{17}, std::size_t{33}
+                })
+        {
+            CAPTURE(length)
+            std::set<std::string> distinct;
+            // (there are 26 and 676 keys of one and two letters)
+            std::size_t wanted = 700;
+            if (length == 1)
+            {
+                wanted = 26;
+            }
+            else if (length == 2)
+            {
+                wanted = 500;
+            }
+            while (distinct.size() < wanted)
+            {
+                std::string key(length, 'a');
+                for (char& c : key)
+                {
+                    c = static_cast<char>('a' + (rng() % 26));
+                }
+                distinct.insert(key);
+            }
+            CHECK(max_displacement(std::vector<std::string>(distinct.begin(), distinct.end())) < nlohmann::detail::view::index_max_displacement);
+        }
+    }
+
+    SECTION("keys of every length that differ in one byte")
+    {
+        // In a large object, a key is found by comparing its bytes with those of the member the
+        // table points to: up to 16 bytes as two overlapping words, longer ones with memcmp.
+        // Keys of every length from 0 to 40, and keys that differ from them in one byte.
+        std::mt19937_64 rng(2026); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+        std::vector<std::string> keys;
+        std::set<std::string> distinct;
+        for (std::size_t length = 0; length <= 40; ++length)
+        {
+            for (int copy = 0; copy < 5; ++copy)
+            {
+                std::string key(length, 'a');
+                for (char& c : key)
+                {
+                    c = static_cast<char>('a' + (rng() % 26));
+                }
+                if (distinct.insert(key).second)
+                {
+                    keys.push_back(key);
+                }
+            }
+        }
+        std::string text = "{";
+        for (std::size_t i = 0; i < keys.size(); ++i)
+        {
+            text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i);
+        }
+        text += "}";
+        REQUIRE(keys.size() >= 128); // (a table is built for 128 members)
+        const json_document d = json_document::parse(text);
+        const json_view v = d.root();
+        for (std::size_t i = 0; i < keys.size(); ++i)
+        {
+            CAPTURE(keys[i])
+            CHECK(v[keys[i]].get<std::size_t>() == i);
+            CHECK(v.at(keys[i]).get<std::size_t>() == i);
+            CHECK(v.contains(keys[i]));
+            for (std::size_t at = 0; at < keys[i].size(); ++at)
+            {
+                std::string other = keys[i];
+                other[at] = other[at] == 'z' ? 'y' : 'z';
+                CAPTURE(other)
+                CHECK(v.contains(other) == (distinct.count(other) != 0));
+            }
+            CHECK(v.contains(keys[i] + "a") == (distinct.count(keys[i] + "a") != 0));
+            if (!keys[i].empty())
+            {
+                CHECK(v.contains(keys[i].substr(1)) == (distinct.count(keys[i].substr(1)) != 0));
+            }
+        }
+    }
+
+    SECTION("shrink_to_fit releases the tables' spare capacity")
+    {
+        const auto make_text = [](int objects, int members)
+        {
+            std::string text = "[";
+            for (int object = 0; object < objects; ++object)
+            {
+                text += object != 0 ? ",{" : "{";
+                for (int i = 0, n = members + object; i < n; ++i)
+                {
+                    text += (i != 0 ? ",\"" : "\"") + std::to_string(i) + "\":" + std::to_string(i);
+                }
+                text += '}';
+            }
+            return text + "]";
+        };
+        const std::string small_text = make_text(5, 150);
+        const std::string big_text = make_text(40, 400);
+
+        // reading a big text, and then a small one, leaves the spare capacity
+        // of the big one: shrink_to_fit() brings the document to the size of
+        // one parsed from the small text alone
+        json_document d = json_document::parse(big_text);
+        const std::size_t big = d.memory_usage();
+        d.read(small_text);
+        CHECK(d.memory_usage() >= big);
+        d.shrink_to_fit();
+        json_document fresh = json_document::parse(small_text);
+        fresh.shrink_to_fit();
+        CHECK(d.memory_usage() == fresh.memory_usage());
+        CHECK(d.memory_usage() < big / 2);
+        CHECK(d.root() == json::parse(small_text));
+        for (int object = 0; object < 5; ++object)
+        {
+            const json_view v = d.root()[static_cast<std::size_t>(object)];
+            for (int i = 0, n = 150 + object; i < n; ++i)
+            {
+                CHECK(v[std::to_string(i)].get<int>() == i);
+            }
+        }
+    }
+
+    SECTION("nested, reused, and in arrays")
+    {
+        std::string inner = "{";
+        for (int i = 0; i < 300; ++i)
+        {
+            inner += (i != 0 ? ",\"m" : "\"m") + std::to_string(i) + "\":" + std::to_string(i);
+        }
+        inner += '}';
+        const std::string text = "[" + inner + ",{\"x\":" + inner + "}," + inner + "]";
+        json_document d = json_document::parse(text);
+        CHECK(d.root()[0]["m299"].get<int>() == 299);
+        CHECK(d.root()[1]["x"]["m150"].get<int>() == 150);
+        CHECK(d.root()[2]["m0"].get<int>() == 0);
+        const std::size_t with_index = d.memory_usage();
+        d.read(std::string("{\"small\": 1}"));
+        CHECK(d.root()["small"].get<int>() == 1);
+        d.read(text);
+        CHECK(d.root()[2]["m7"].get<int>() == 7);
+        CHECK(d.memory_usage() >= with_index / 2);
+    }
+}

tests/src/unit-json_view_macros.cpp

@@ -25,7 +25,7 @@
 #endif
 
 // the view's own macros do not leak
-#if defined(NLOHMANN_VIEW_LIKELY) || defined(NLOHMANN_VIEW_UNLIKELY) || defined(NLOHMANN_VIEW_ALWAYS_INLINE) || defined(NLOHMANN_VIEW_NOINLINE) \
+#if defined(NLOHMANN_VIEW_LIKELY) || defined(NLOHMANN_VIEW_UNLIKELY) || defined(NLOHMANN_VIEW_ALWAYS_INLINE) || defined(NLOHMANN_VIEW_NOINLINE) || defined(NLOHMANN_VIEW_NOCLONE) \
     || defined(NLOHMANN_VIEW_NODISCARD) || defined(NLOHMANN_VIEW_THROW) || defined(NLOHMANN_VIEW_HAS_CPP_17) || defined(NLOHMANN_VIEW_LITTLE_ENDIAN) \
     || defined(NLOHMANN_VIEW_REPEAT16)
     #error "json_view.hpp leaks a macro"

tests/src/unit-json_view_positions.cpp

@@ -81,6 +81,112 @@ std::string range(const json& j)
 {
     return j.start_pos() == npos && j.end_pos() == npos ? "none" : std::to_string(j.start_pos()) + "-" + std::to_string(j.end_pos());
 }
+
+#if !defined(JSON_NOEXCEPTION)
+using json_view_test::exception_of_call;
+
+// the exceptions about every value of v are those about the value at the same
+// place in j, a value of the whole document from parse() or materialize() (so
+// that its parents and positions are set); members whose key repeats are
+// skipped (the view finds the first one, j holds the last)
+template<typename View>
+void check_exceptions(const View& v, const json& j)
+{
+    CAPTURE(j.dump())
+    if (!v.is_number())
+    {
+        CHECK(exception_of_call([&] { static_cast<void>(v.template get<int>()); }) == exception_of_call([&] { static_cast<void>(j.get<int>()); }));
+    }
+    if (!v.is_string())
+    {
+        CHECK(exception_of_call([&] { static_cast<void>(v.template get<std::string>()); }) == exception_of_call([&] { static_cast<void>(j.get<std::string>()); }));
+    }
+    if (!v.is_array())
+    {
+        CHECK(exception_of_call([&] { static_cast<void>(v.template get<std::vector<int>>()); }) == exception_of_call([&] { static_cast<void>(j.get<std::vector<int>>()); }));
+    }
+    CHECK(exception_of_call([&] { static_cast<void>(v.at("missing")); }) == exception_of_call([&] { static_cast<void>(j.at("missing")); }));
+    CHECK(exception_of_call([&] { static_cast<void>(v.at(1000)); }) == exception_of_call([&] { static_cast<void>(j.at(1000)); }));
+    CHECK(exception_of_call([&] { static_cast<void>(v.at(json::json_pointer("/missing"))); }) == exception_of_call([&] { static_cast<void>(j.at(json::json_pointer("/missing"))); }));
+    CHECK(exception_of_call([&] { static_cast<void>(v.at(json::json_pointer("/-"))); }) == exception_of_call([&] { static_cast<void>(j.at(json::json_pointer("/-"))); }));
+    CHECK(exception_of_call([&] { static_cast<void>(v.value("k", 0)); }) == exception_of_call([&] { static_cast<void>(j.value("k", 0)); }));
+    if (!v.is_object())
+    {
+        CHECK(exception_of_call([&] { static_cast<void>(v["k"]); }) == exception_of_call([&] { static_cast<void>(j["k"]); }));
+        // (without the context of basic_json: view iterators do not know the value they iterate over)
+        CHECK(exception_of_call([&] { static_cast<void>(v.begin().key()); }) == "[json.exception.invalid_iterator.207] cannot use key() for non-object iterators");
+    }
+    if (!v.is_array())
+    {
+        CHECK(exception_of_call([&] { static_cast<void>(v[0]); }) == exception_of_call([&] { static_cast<void>(j[0]); }));
+    }
+    if (v.is_null())
+    {
+        CHECK(exception_of_call([&] { static_cast<void>(v.front()); }) == exception_of_call([&] { static_cast<void>(j.front()); }));
+    }
+    if (v.is_object())
+    {
+        for (auto it = v.begin(); it != v.end(); ++it)
+        {
+            const std::string key(it.key().data(), it.key().size());
+            if (v.count(key) == 1)
+            {
+                check_exceptions(it.value(), j.at(key));
+            }
+        }
+    }
+    else if (v.is_array())
+    {
+        for (std::size_t i = 0; i < v.size(); ++i)
+        {
+            check_exceptions(v[i], j[i]);
+        }
+    }
+}
+
+// as check_exceptions, for edits that fail (they change neither d nor j)
+void check_edit_exceptions(json_editable_document& d, const json_editable_document::view_type& v, json& j)
+{
+    CAPTURE(j.dump())
+    if (!v.is_object() && !v.is_null())
+    {
+        CHECK(exception_of_call([&] { d.set(v, "k", 1); }) == exception_of_call([&] { j["k"] = 1; }));
+        CHECK(exception_of_call([&] { d.erase(v, "k"); }) == exception_of_call([&] { j.erase("k"); }));
+    }
+    if (!v.is_array() && !v.is_null())
+    {
+        CHECK(exception_of_call([&] { d.set(v, 0, 1); }) == exception_of_call([&] { j[0] = 1; }));
+        CHECK(exception_of_call([&] { d.push_back(v, 1); }) == exception_of_call([&] { j.push_back(1); }));
+    }
+    if (!v.is_array())
+    {
+        CHECK(exception_of_call([&] { d.insert(v, 0, 1); }) == exception_of_call([&] { j.insert(j.cbegin(), 1); }));
+        CHECK(exception_of_call([&] { d.erase(v, 0); }) == exception_of_call([&] { j.erase(0); }));
+    }
+    else
+    {
+        CHECK(exception_of_call([&] { d.erase(v, 1000); }) == exception_of_call([&] { j.erase(1000); }));
+    }
+    if (v.is_object())
+    {
+        for (auto it = v.begin(); it != v.end(); ++it)
+        {
+            const std::string key(it.key().data(), it.key().size());
+            if (v.count(key) == 1)
+            {
+                check_edit_exceptions(d, it.value(), j.at(key));
+            }
+        }
+    }
+    else if (v.is_array())
+    {
+        for (std::size_t i = 0; i < v.size(); ++i)
+        {
+            check_edit_exceptions(d, v[i], j[i]);
+        }
+    }
+}
+#endif
 } // namespace
 
 TEST_CASE("json_view materialize() source positions")
@@ -345,3 +451,123 @@ TEST_CASE("json_view materialize() source positions")
     }
 #endif
 }
+
+#if !defined(JSON_NOEXCEPTION)
+TEST_CASE("json_view exceptions name the path and the bytes of the value")
+{
+    SECTION("as those of basic_json")
+    {
+        const std::vector<std::string> texts =
+        {
+            "null", "true", "42", "\"s\"", "[]", "{}", "[1, [2, [3, []]]]", R"({"a": {"b": [1, {"c": null}]}, "d": "e"})",
+            R"({"a/b": {"~": [1]}, "\u0041\n": {"x": "\t"}, "": [{}]})",
+            R"([1 /* ] */, {"a": [] // }
+, "b": {} } , ])",
+            "\n\t[\r\n  1 ,\n  {\n    \"a\" : [ ]\n  }\n]\n",
+        };
+        for (const auto& text : texts)
+        {
+            CAPTURE(text)
+            const json j = json::parse(text, nullptr, true, true, true);
+            const json_document d = json_document::parse(text, true, true, true);
+            check_exceptions(d.root(), j);
+            json_editable_document e = json_editable_document::parse(text, true, true, true);
+            check_exceptions(e.root(), j);
+            json m = e.root().materialize();
+            check_edit_exceptions(e, e.root(), m);
+        }
+    }
+
+    SECTION("generated documents")
+    {
+        json_view_test::generator gen;
+        for (int i = 0; i < 100; ++i)
+        {
+            std::string text;
+            gen.value(text, 0);
+            CAPTURE(text)
+            const json_document d = json_document::parse(text);
+            check_exceptions(d.root(), json::parse(text));
+        }
+    }
+
+    SECTION("edited documents: as those of materialize()")
+    {
+        const std::string text = R"({"a": [1, 2], "b": {"c": "\n", "d": true}, "e": [3, [4]], "f": "x"})";
+        json_editable_document d = json_editable_document::parse(text);
+        d.set(d.root()["f"], 5);
+        d.push_back(d.root()["a"], json::parse(R"({"n": [null]})"));
+        d.erase(d.root()["e"], 0);
+        d.set(d.root()["b"], "c2", d.root()["e"]);
+        d.insert(d.root()["e"], 0, "new");
+        json m = d.root().materialize();
+        check_exceptions(d.root(), m);
+        check_edit_exceptions(d, d.root(), m);
+        // (a value inside a new container: a path, but no bytes)
+        std::string expected = "[json.exception.type_error.302] ";
+#if JSON_DIAGNOSTICS
+        expected += "(/a/2/n/0) ";
+#endif
+        expected += "type must be number, but is null";
+        CHECK(exception_of_call([&] { static_cast<void>(d.root()["a"][2]["n"][0].get<int>()); }) == expected);
+    }
+
+    SECTION("deep documents with siblings after every nested container")
+    {
+        // the search for the path pushes and pops one frame per level (the
+        // stack reallocates while it grows, and shrinks again at every
+        // sibling): run under a sanitizer, a reference to a popped or moved
+        // frame would show here
+        std::string text = "7";
+        for (int level = 0; level < 40; ++level)
+        {
+            text = R"([[1, [2]], )" + text + R"(, {"k": [3, {"l": [4]}]}, [5, [6, [7]]]])";
+        }
+        CAPTURE(text)
+        const json j = json::parse(text);
+        const json_document d = json_document::parse(text);
+        check_exceptions(d.root(), j);
+        json_editable_document e = json_editable_document::parse(text);
+        e.set(e.root()[0][0], 9);
+        check_exceptions(e.root(), e.root().materialize());
+    }
+
+    SECTION("examples")
+    {
+        const std::string text = R"({"people": [{"name": "a", "age": 1}, {"name": "c", "age": "x"}], "o": {"k": 1}})";
+        const json_document d = json_document::parse(text);
+        std::string expected_age = "[json.exception.type_error.302] ";
+#if JSON_DIAGNOSTICS
+        expected_age += "(/people/1/age) ";
+#endif
+        expected_age += "(bytes 58-61) type must be number, but is string";
+        CHECK(exception_of_call([&] { static_cast<void>(d.root()["people"][1]["age"].get<int>()); }) == expected_age);
+
+        std::string expected_zz = "[json.exception.out_of_range.403] ";
+#if JSON_DIAGNOSTICS
+        expected_zz += "(/people/0) ";
+#endif
+        expected_zz += "(bytes 12-35) key 'zz' not found";
+        CHECK(exception_of_call([&] { static_cast<void>(d.root().at(json::json_pointer("/people/0/zz"))); }) == expected_zz);
+
+        // the root has no path, and with JSON_DIAGNOSTICS then no bytes either (as basic_json)
+        std::string expected_missing = "[json.exception.out_of_range.403] ";
+#if !JSON_DIAGNOSTICS
+        expected_missing += "(bytes 0-79) ";
+#endif
+        expected_missing += "key 'missing' not found";
+        CHECK(exception_of_call([&] { static_cast<void>(d.root().at("missing")); }) == expected_missing);
+    }
+
+    SECTION("duplicate keys: the value the view finds")
+    {
+        const json_document d = json_document::parse(R"({"x": "1", "x": "22"})");
+        std::string expected = "[json.exception.type_error.302] ";
+#if JSON_DIAGNOSTICS
+        expected += "(/x) ";
+#endif
+        expected += "(bytes 6-9) type must be number, but is string";
+        CHECK(exception_of_call([&] { static_cast<void>(d.root()["x"].get<int>()); }) == expected);
+    }
+}
+#endif

tests/src/unit-msgpack.cpp

@@ -27,12 +27,15 @@ using nlohmann::json;
 #include <sstream>
 #include <iomanip>
 #include <limits>
+#include <list>
 #include <set>
 #include "make_test_data_available.hpp"
 #include "round_trip_corpus.hpp"
 #include "test_utils.hpp"
 #include "sax_countdown.hpp"
+#include "sax_event_loggers.hpp"
 using utils::SaxCountdown;
+using utils::SaxEventLogger;
 
 
 TEST_CASE("MessagePack")
@@ -2212,3 +2215,99 @@ TEST_CASE("MessagePack large strings and binaries (chunked reader)")
         }
     }
 }
+
+TEST_CASE("MessagePack arrays of scalars from contiguous and non-contiguous input")
+{
+    // contiguous input reads the integers, floats, booleans, and nils an
+    // array begins with in one loop, other input value by value; both must
+    // give the same events, value, or error for the complete document and for
+    // every truncation of it, and stop at every event a SAX handler rejects
+    const std::vector<std::uint8_t> msgpack =
+    {
+        0x83,                                                       // map(3)
+        0xA1, 'a',                                                  // "a"
+        0xDC, 0x00, 0x16,                                           // array 16 (22)
+        0x00, 0x7F, 0xCC, 0xFF, 0xCD, 0x01, 0x00,                   // 0, 127, 255, 256
+        0xCE, 0x00, 0x01, 0x00, 0x00,                               // 65536
+        0xCF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,       // 18446744073709551615
+        0xFF, 0xE0, 0xD0, 0x80, 0xD1, 0xFF, 0x00,                   // -1, -32, -128, -256
+        0xD2, 0xFF, 0xFE, 0xFF, 0xFF,                               // -65537
+        0xD3, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,       // -9223372036854775808
+        0xC2, 0xC3, 0xC0,                                           // false, true, nil
+        0xCA, 0x3F, 0xC0, 0x00, 0x00,                               // 1.5 (float 32)
+        0xCB, 0xBF, 0xB9, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9A,       // -0.1
+        0xA1, 'x',                                                  // "x" (ends the loop)
+        0x01,                                                       // 1
+        0xCB, 0x40, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,       // 2.5
+        0xD9, 0x01, 'y',                                            // "y" (str 8)
+        0xC0,                                                       // nil
+        0xA1, 'b',                                                  // "b"
+        0x93,                                                       // fixarray(3)
+        0x92, 0xCB, 0x3F, 0xF4, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // [1.25,
+        0xCB, 0xC0, 0x0E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,       //  -3.75]
+        0x92, 0xCB, 0x3F, 0xF4, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // [1.25,
+        0xCB, 0xC0, 0x0E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,       //  -3.75]
+        0x90,                                                       // []
+        0xA1, 'c',                                                  // "c"
+        0x94, 0x80, 0x01, 0xC4, 0x01, 0x05, 0x91, 0x03              // [{}, 1, bin 8, [3]]
+    };
+
+    const json j = json::from_msgpack(msgpack);
+    CHECK(j["a"].size() == 22);
+    CHECK(j["a"][5] == 18446744073709551615u);
+    CHECK(j["a"][7] == -32);
+    CHECK(j["a"][11] == (std::numeric_limits<std::int64_t>::min)());
+    CHECK(j["a"][15] == 1.5);
+    CHECK(j["a"][16] == -0.1);
+    CHECK(j["a"][17] == "x");
+    CHECK(j["b"] == json::parse("[[1.25, -3.75], [1.25, -3.75], []]"));
+    CHECK(j["c"][2].is_binary());
+
+    for (std::size_t length = 0; length <= msgpack.size(); ++length)
+    {
+        CAPTURE(length)
+        const std::vector<std::uint8_t> contiguous(msgpack.begin(), msgpack.begin() + static_cast<std::ptrdiff_t>(length));
+        const std::list<std::uint8_t> bytewise(contiguous.begin(), contiguous.end());
+
+        CHECK(json::from_msgpack(contiguous, true, false).dump() == json::from_msgpack(bytewise.begin(), bytewise.end(), true, false).dump());
+#if !defined(JSON_NOEXCEPTION)
+        std::string contiguous_error;
+        std::string bytewise_error;
+        try
+        {
+            json _;
+            _ = json::from_msgpack(contiguous);
+        }
+        catch (const json::parse_error& e)
+        {
+            contiguous_error = e.what();
+        }
+        try
+        {
+            json _;
+            _ = json::from_msgpack(bytewise.begin(), bytewise.end());
+        }
+        catch (const json::parse_error& e)
+        {
+            bytewise_error = e.what();
+        }
+        CHECK(contiguous_error == bytewise_error);
+#endif
+
+        SaxEventLogger from_contiguous;
+        SaxEventLogger from_bytewise;
+        CHECK(json::sax_parse(contiguous, &from_contiguous, json::input_format_t::msgpack)
+              == json::sax_parse(bytewise.begin(), bytewise.end(), &from_bytewise, json::input_format_t::msgpack));
+        CHECK(from_contiguous.events == from_bytewise.events);
+    }
+
+    for (int events = 0; events <= 60; ++events)
+    {
+        CAPTURE(events)
+        const std::list<std::uint8_t> bytewise(msgpack.begin(), msgpack.end());
+        SaxCountdown from_contiguous(events);
+        SaxCountdown from_bytewise(events);
+        CHECK(json::sax_parse(msgpack, &from_contiguous, json::input_format_t::msgpack)
+              == json::sax_parse(bytewise.begin(), bytewise.end(), &from_bytewise, json::input_format_t::msgpack));
+    }
+}

tests/src/unit-serialization.cpp

@@ -23,6 +23,7 @@ using nlohmann::json;
 #include <cstdint>
 #include <sstream>
 #include <iomanip>
+#include <limits>
 #include <string>
 #include <vector>
 
@@ -248,6 +249,51 @@ TEST_CASE_TEMPLATE("serialization for extreme integer values", T, int32_t, uint3
     }
 }
 
+TEST_CASE("integers of every digit count are written like std::to_string")
+{
+    // dump_integer() writes up to 16 digits in two groups of eight and 17 to
+    // 20 digits as one to four digits and two groups of eight
+    std::vector<std::uint64_t> values;
+    std::uint64_t power = 1;
+    for (int digits = 1; digits <= 20; ++digits)
+    {
+        values.push_back(power);                     // 1 followed by zeros
+        values.push_back(power + 1);
+        values.push_back((power * 2) - 1);
+        if (digits < 20)
+        {
+            values.push_back((power * 10) - 1);      // all 9s
+            values.push_back((power * 10) - power);  // 9 followed by zeros
+            power *= 10;
+        }
+    }
+    values.push_back((std::numeric_limits<std::uint64_t>::max)());
+    values.push_back(static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()));
+    values.push_back(static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()) + 1);
+    std::uint64_t state = 0x9E3779B97F4A7C15u;
+    for (int i = 0; i < 20000; ++i)
+    {
+        state = (state * 6364136223846793005u) + 1442695040888963407u;
+        values.push_back(state >> (state % 61));     // every bit length
+    }
+
+    for (const auto v : values)
+    {
+        CAPTURE(v)
+        CHECK(json(v).dump() == std::to_string(v));
+        if (v <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
+        {
+            const auto s = static_cast<std::int64_t>(v);
+            CHECK(json(s).dump() == std::to_string(s));
+            CHECK(json(-s).dump() == std::to_string(-s));
+        }
+    }
+    CHECK(json((std::numeric_limits<std::int64_t>::min)()).dump() == "-9223372036854775808");
+
+    // in a container, so the digits are followed by other output
+    CHECK(json::array({std::uint64_t{18446744073709551615u}, std::int64_t{-1234567890123456789}, 1}).dump() == "[18446744073709551615,-1234567890123456789,1]");
+}
+
 TEST_CASE("dump with binary values")
 {
     auto binary = json::binary({1, 2, 3, 4});

tests/src/unit-ubjson.cpp

@@ -21,12 +21,15 @@ using nlohmann::json;
 
 #include <iostream>
 #include <fstream>
+#include <list>
 #include <set>
 #include "make_test_data_available.hpp"
 #include "round_trip_corpus.hpp"
 #include "test_utils.hpp"
 #include "sax_countdown.hpp"
+#include "sax_event_loggers.hpp"
 using utils::SaxCountdown;
+using utils::SaxEventLogger;
 
 
 TEST_CASE("UBJSON")
@@ -3400,3 +3403,72 @@ TEST_CASE("UBJSON optimized container type marker is validated for count 0")
         }
     }
 }
+
+TEST_CASE("UBJSON optimized arrays from contiguous and non-contiguous input")
+{
+    // contiguous input reads the numbers of an array with a type marker in
+    // one loop, other input number by number; both must give the same events,
+    // value, or error for the complete document and for every truncation of
+    // it, and stop at every event a SAX handler rejects
+    json document =
+    {
+        {"u8", {0, 200, 255}},
+        {"i8", {-5, 100, -128}},
+        {"i16", {-30000, 1000, 30000}},
+        {"i32", {-2000000000, 5, 70000}},
+        {"i64", {-9000000000000000000LL, 1, 5000000000LL}},
+        {"f64", {1.5, -0.1, 2.5}},
+        {"pairs", {{1.25, -3.75}, {1.25, -3.75}, json::array()}},
+        {"mixed", {1, "a", 2.5, nullptr}},
+    };
+    const std::vector<std::uint8_t> encoded = json::to_ubjson(document, true, true);
+    CHECK(json::from_ubjson(encoded) == document);
+
+    for (std::size_t length = 0; length <= encoded.size(); ++length)
+    {
+        CAPTURE(length)
+        const std::vector<std::uint8_t> contiguous(encoded.begin(), encoded.begin() + static_cast<std::ptrdiff_t>(length));
+        const std::list<std::uint8_t> bytewise(contiguous.begin(), contiguous.end());
+
+        CHECK(json::from_ubjson(contiguous, true, false).dump() == json::from_ubjson(bytewise.begin(), bytewise.end(), true, false).dump());
+#if !defined(JSON_NOEXCEPTION)
+        std::string contiguous_error;
+        std::string bytewise_error;
+        try
+        {
+            json _;
+            _ = json::from_ubjson(contiguous);
+        }
+        catch (const json::exception& e)
+        {
+            contiguous_error = e.what();
+        }
+        try
+        {
+            json _;
+            _ = json::from_ubjson(bytewise.begin(), bytewise.end());
+        }
+        catch (const json::exception& e)
+        {
+            bytewise_error = e.what();
+        }
+        CHECK(contiguous_error == bytewise_error);
+#endif
+
+        SaxEventLogger from_contiguous;
+        SaxEventLogger from_bytewise;
+        CHECK(json::sax_parse(contiguous, &from_contiguous, json::input_format_t::ubjson)
+              == json::sax_parse(bytewise.begin(), bytewise.end(), &from_bytewise, json::input_format_t::ubjson));
+        CHECK(from_contiguous.events == from_bytewise.events);
+    }
+
+    for (int events = 0; events <= 80; ++events)
+    {
+        CAPTURE(events)
+        const std::list<std::uint8_t> bytewise(encoded.begin(), encoded.end());
+        SaxCountdown from_contiguous(events);
+        SaxCountdown from_bytewise(events);
+        CHECK(json::sax_parse(encoded, &from_contiguous, json::input_format_t::ubjson)
+              == json::sax_parse(bytewise.begin(), bytewise.end(), &from_bytewise, json::input_format_t::ubjson));
+    }
+}

tests/src/unit-unicode.cpp

@@ -13,6 +13,7 @@ using nlohmann::json;
 
 #include <algorithm>
 #include <fstream>
+#include <random>
 #include <string>
 #include "make_test_data_available.hpp"
 #include "test_utils.hpp"
@@ -1631,3 +1632,40 @@ TEST_CASE("Unicode RFC 3629")
 }
 
 DOCTEST_CLANG_SUPPRESS_WARNING_POP
+
+TEST_CASE("UTF-8 check of whole strings")
+{
+    // valid_utf8_string() decides short strings with a word test and long ones
+    // 16 bytes at a time where a vector check is available; it must agree with
+    // the byte-wise check for every mix of ASCII, sequences of each length,
+    // ill-formed and truncated sequences, at every length and offset
+    const char* const pieces[] = // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+    {
+        "a", "\x7F", "\xC3\xA9", "\xE2\x82\xAC", "\xE0\xA0\x80", "\xEF\xBF\xBF", "\xF0\x9F\x98\x80", "\xF4\x8F\xBF\xBF",
+        "\x80", "\xC0\xAF", "\xC3", "\xE2\x82", "\xED\xA0\x80", "\xF0\x9F", "\xF4\x90\x80\x80", "\xFF"
+    };
+    // std::mt19937's sequence is fixed by the standard; no distribution is used
+    std::mt19937 rng(5); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+    std::size_t valid = 0;
+    for (int i = 0; i < 100000; ++i)
+    {
+        std::string s;
+        const std::size_t length = rng() % 100;
+        const auto ascii = static_cast<std::uint32_t>(rng() % 101);
+        while (s.size() < length)
+        {
+            // mostly well-formed pieces (the first eight), so that long valid
+            // strings are common
+            s += (rng() % 100 < ascii) ? std::string("x") : std::string(pieces[rng() % (rng() % 8 == 0 ? 16 : 8)]);
+        }
+        const auto* data = reinterpret_cast<const unsigned char*>(s.data());
+        const bool expected = nlohmann::detail::is_valid_utf8(s);
+        valid += expected ? 1 : 0;
+        CAPTURE(s)
+        CHECK(nlohmann::detail::valid_utf8_string(data, s.size()) == expected);
+        CHECK((nlohmann::detail::valid_utf8_prefix(data, s.size()) == s.size()) == expected);
+    }
+    // both outcomes are common enough to be tested
+    CHECK(valid > 20000);
+    CHECK(valid < 80000);
+}

tools/generate_natvis/README.md

@@ -6,6 +6,11 @@ The checked-in `nlohmann_json.natvis` covers the default namespace (no ABI tags)
 of ABI tags, with both versioned and unversioned namespace variants. Configurations that enable three or more ABI tags
 are not covered by this reduced file; use `--abi-tags` or `--all` (see below) to generate a file for them.
 
+The visualizers of `basic_json_document` and `basic_json_view` live in the same inline namespaces as `basic_json`, so the
+ABI tags apply to them in the same way, and the `view_mode` template argument is covered by a wildcard: it does not
+multiply the namespaces. Each namespace gets three more types (`basic_json_view<*,*>`, `basic_json_document<*,*>`, and
+`detail::view::node`), which roughly doubles the size of the file.
+
 The ABI tag list and the library version are parsed from
 `include/nlohmann/detail/abi_macros.hpp`, so this script must be re-run (via
 `make natvis`) whenever an `NLOHMANN_JSON_ABI_TAG_*` macro is added to that
@@ -35,7 +40,7 @@ version other than the one in `abi_macros.hpp`.
 |-------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | `--list-tags`     | Print every ABI tag (in namespace order) with the macro that enables it and the `NLOHMANN_JSON_ABI_TAG_*` identifier, then exit.                                                                                                                    |
 | `--abi-tags TAGS` | Add the namespaces of one configuration, given as a comma-separated list of ABI tags (`_diag,_dp,_ns`; the leading underscore is optional, and the order does not matter). Can be repeated for several configurations. Unknown tags are an error. |
-| `--all`           | Generate the namespaces for every combination of ABI tags. The file size doubles with each tag (about 60 MB for 12 tags). Cannot be combined with `--abi-tags`.                                                                                    |
+| `--all`           | Generate the namespaces for every combination of ABI tags. The file size doubles with each tag (about 60 MB for 11 tags). Cannot be combined with `--abi-tags`.                                                                                    |
 | `--output FILE`   | Write the Natvis file to `FILE` instead of `nlohmann_json.natvis` in the repository root.                                                                                                                                                           |
 
 Each configuration gets both the versioned (`json_abi_diag_dp_ns_v3_12_0`) and the unversioned (`json_abi_diag_dp_ns`,

tools/generate_natvis/generate_natvis.py

@@ -95,7 +95,7 @@ if __name__ == '__main__':
                                 'optional) of one configuration to add to the default namespaces; can be repeated')
     selection.add_argument('--all', action='store_true',
                            help='Generate the namespaces for every combination of ABI tags; the file size doubles '
-                                'with each ABI tag (about 60 MB for 12 tags)')
+                                'with each ABI tag (about 60 MB for 11 tags)')
     parser.add_argument('--list-tags', action='store_true',
                         help='List the ABI tags with the macros that enable them, and exit')
     parser.add_argument('--output', metavar='FILE',

tools/generate_natvis/nlohmann_json.natvis.j2

@@ -5,6 +5,39 @@
 <!-- * * * * * * * * AUTO-GENERATED FILE  * * * * * * * * -->
 
 <AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
+{# The children of the container node `node` (a pointer expression) of the document `doc` (a document_data pointer
+   expression). A node is only an index into the source text: strings are read from `doc`, so the strings of the
+   direct children are readable here, but the children of a nested container are shown as nodes (see the node
+   visualizer below). Containers with edits (flag 8, "moved") are not expanded. The node kinds are the numbers of
+   node_kind: 1 object, 2 array, 3 string; the float token is shown only by the node visualizer. #}
+{% macro children(node, doc=none) %}
+            <CustomListItems MaxItemsPerView="1000">
+              <Variable Name="nd" InitialValue="{{ node }}" />
+              <Variable Name="obj" InitialValue="nd != 0 &amp;&amp; (int)nd-&gt;kind == 1" />
+              <Variable Name="n" InitialValue="(nd != 0 &amp;&amp; ((int)nd-&gt;kind == 1 || (int)nd-&gt;kind == 2) &amp;&amp; (nd-&gt;flags &amp; 8) == 0) ? (int)nd-&gt;len : 0" />
+              <Variable Name="p" InitialValue="nd + 1" />
+              <Variable Name="i" InitialValue="0" />
+              <Size>obj ? 2 * n : n</Size>
+              <Loop Condition="i &lt; n">
+{% if doc %}
+                <Item Name="key" Condition="obj">{{ doc }}-&gt;base._Elems[p-&gt;flags &amp; 3] + p-&gt;off,[p-&gt;len]s8</Item>
+{% else %}
+                <Item Name="key" Condition="obj">*p</Item>
+{% endif %}
+                <Exec Condition="obj">p = p + 1</Exec>
+{% if doc %}
+                <Item Name="value" Condition="obj &amp;&amp; (int)p-&gt;kind == 3">{{ doc }}-&gt;base._Elems[p-&gt;flags &amp; 3] + p-&gt;off,[p-&gt;len]s8</Item>
+{% endif %}
+                <Item Name="value" Condition="obj{% if doc %} &amp;&amp; (int)p-&gt;kind != 3{% endif %}">*p</Item>
+{% if doc %}
+                <Item Condition="!obj &amp;&amp; (int)p-&gt;kind == 3">{{ doc }}-&gt;base._Elems[p-&gt;flags &amp; 3] + p-&gt;off,[p-&gt;len]s8</Item>
+{% endif %}
+                <Item Condition="!obj{% if doc %} &amp;&amp; (int)p-&gt;kind != 3{% endif %}">*p</Item>
+                <Exec>p = p + (((int)p-&gt;kind == 1 || (int)p-&gt;kind == 2) ? p-&gt;next : 1)</Exec>
+                <Exec>i = i + 1</Exec>
+              </Loop>
+            </CustomListItems>
+{%- endmacro %}
 {% for ns in namespaces %}
     <!-- Namespace {{ ns }} -->
     <Type Name="{{ ns }}::basic_json&lt;*&gt;">
@@ -62,5 +95,44 @@
     </Type>
 
 {% endfor %}
+
+    <!-- json_view / json_document (include/nlohmann/json_view.hpp). They live in the same inline namespaces as
+         basic_json, so the ABI tags need no extra entries; the view_mode is a template argument that the wildcard
+         covers. A view is a pointer to the document's data and a pointer to a node of its flat index; the
+         strings of the source are found through document_data::base (std::array of the MSVC STL: _Elems). -->
+    <Type Name="{{ ns }}::detail::view::node">
+        <DisplayString Condition="(int)kind == 0">null</DisplayString>
+        <DisplayString Condition="(int)kind == 1">object, size={len}</DisplayString>
+        <DisplayString Condition="(int)kind == 2">array, size={len}</DisplayString>
+        <DisplayString Condition="(int)kind == 3">string, length={len}</DisplayString>
+        <DisplayString Condition="(int)kind == 4">boolean: {(flags &amp; 4) != 0}</DisplayString>
+        <DisplayString Condition="(int)kind == 5">int64: {(__int64)((unsigned __int64)len | ((unsigned __int64)next &lt;&lt; 32))}</DisplayString>
+        <DisplayString Condition="(int)kind == 6">uint64: {(unsigned __int64)len | ((unsigned __int64)next &lt;&lt; 32)}</DisplayString>
+        <DisplayString Condition="(int)kind == 7">float, length={len}</DisplayString>
+        <DisplayString>link</DisplayString>
+        <Expand>
+{{ children('this') }}
+        </Expand>
+    </Type>
+
+    <Type Name="{{ ns }}::basic_json_view&lt;*,*&gt;">
+        <DisplayString Condition="m_node == 0">discarded</DisplayString>
+        <DisplayString Condition="(int)m_node-&gt;kind == 3">{m_doc-&gt;base._Elems[m_node-&gt;flags &amp; 3] + m_node-&gt;off,[m_node-&gt;len]s8}</DisplayString>
+        <DisplayString Condition="(int)m_node-&gt;kind == 7">{m_doc-&gt;base._Elems[m_node-&gt;flags &amp; 3] + m_node-&gt;off,[m_node-&gt;len]s8b}</DisplayString>
+        <DisplayString>{*m_node}</DisplayString>
+        <Expand>
+{{ children('m_node', 'm_doc') }}
+        </Expand>
+    </Type>
+
+    <Type Name="{{ ns }}::basic_json_document&lt;*,*&gt;">
+        <DisplayString Condition="m_data._Mypair._Myval2 == 0 || m_data._Mypair._Myval2-&gt;discarded">discarded</DisplayString>
+        <DisplayString>{*m_data._Mypair._Myval2-&gt;nodes}</DisplayString>
+        <Expand>
+            <Item Name="[source]" Condition="m_data._Mypair._Myval2 != 0">m_data._Mypair._Myval2-&gt;src,[m_data._Mypair._Myval2-&gt;size]s8b</Item>
+            <Item Name="[nodes]" Condition="m_data._Mypair._Myval2 != 0">m_data._Mypair._Myval2-&gt;node_count</Item>
+{{ children('m_data._Mypair._Myval2->nodes', 'm_data._Mypair._Myval2') }}
+        </Expand>
+    </Type>
 {% endfor %}
 </AutoVisualizer>