json_view: exceptions name the path and the bytes of the value

With JSON_DIAGNOSTICS and JSON_DIAGNOSTIC_POSITIONS, the exceptions of views
now carry the same context as those of basic_json: "(/path) " and
"(bytes a-b) " in front of the message, in basic_json's format (with
JSON_DIAGNOSTICS, no context for the root). Before, views threw without any
context, and since get<T>() reads the view directly, conversions had lost
even the relative path they used to get through materialize().

The throw helpers of detail/view/errors.hpp take an error_site (document
and node; empty without the two macros). Only on the error path, the path is
found by descending from the root (pruned by subtree extent before the first
edit, a full walk through edited sequences after), and the bytes as
materialize() sets them (position_source; a container's end by following the
chain of last elements and scanning to the closing brackets). from_json() for
views and the strict enum macro put the same context in front through
exception_prefix(). Iterators keep their container only under the two
macros, for key(). Without the macros, the accessors compile to the same
code as before.

Tests compare every value's exceptions with those of the parsed or
materialized basic_json value, including edited documents; the checks that
were disabled under the two macros run again.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

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
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
-`JSON_DIAGNOSTICS` enabled.
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) these exceptions name the JSON
+Pointer path of the value within the document, and with
+[`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) its bytes in the source text (where
+[`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
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
-`JSON_DIAGNOSTICS` enabled.
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the exception names the JSON Pointer
+path of the value within the document, and with [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md)
+its bytes in the source text (where [`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
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
-`JSON_DIAGNOSTICS` enabled.
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the exception names the JSON Pointer
+path of the value within the document, and with [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md)
+its bytes in the source text (where [`materialize()`](materialize.md) sets them).
 
 ## Complexity
 

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

@@ -80,14 +80,13 @@ 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
-bullets above) carry a
-[`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no `BasicJsonType` value to point at. An
-exception thrown while converting through `materialize()` (the last bullet) is different: it is thrown by a real
-`BasicJsonType` value, so it **does** carry a `JSON_DIAGNOSTICS` path if `BasicJsonType` was built with it enabled.
-That path is relative to the root of the view's subtree, because `materialize()` builds only the subtree (with parent
-pointers): it is empty if the failing value is the subtree's root itself, and it never is the path within the whole
-document.
+The exceptions thrown directly by this function or by a `from_json()` that reads the view (the first four bullets
+above) carry the context of those of `BasicJsonType`: with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the
+JSON Pointer path of the value within the document, and with
+[`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) its bytes in the source text. An exception
+thrown while converting through `materialize()` (the last bullet) is thrown by the materialized `BasicJsonType` value
+instead: its path is relative to the root of the view's subtree, because `materialize()` builds only the subtree
+(with parent pointers), so it is empty if the failing value is the subtree's root itself.
 
 ## 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
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
-`JSON_DIAGNOSTICS` enabled.
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the exception names the JSON Pointer
+path of the value within the document, and with [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md)
+its bytes in the source text (where [`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
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
-`JSON_DIAGNOSTICS` enabled.
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) the exception names the JSON Pointer
+path of the value within the document, and with [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md)
+its bytes in the source text (where [`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
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
-`JSON_DIAGNOSTICS` enabled.
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) these exceptions name the JSON
+Pointer path of the value within the document, and with
+[`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) its bytes in the source text (where
+[`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
-`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
-`JSON_DIAGNOSTICS` enabled.
+As for `BasicJsonType`, with [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) these exceptions name the JSON
+Pointer path of the value within the document, and with
+[`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) its bytes in the source text (where
+[`materialize()`](materialize.md) sets them).
 
 ## Complexity
 

docs/mkdocs/docs/features/json_view.md

@@ -134,9 +134,12 @@ 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)
-  needs parent pointers in `basic_json` values) or only affect the values `materialize()` produces, through
-  `BasicJsonType`.
+  how it reports errors. With [`JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md) and
+  [`JSON_DIAGNOSTIC_POSITIONS`](../api/macros/json_diagnostic_positions.md), the exceptions of views name the path
+  and the bytes of the value as those of `#!cpp basic_json` do; as a view has neither parent pointers nor stored
+  positions, both are found from the document's index when the exception is thrown, which takes time linear in the
+  size of the document (only for an exception). The other macros only affect the values `materialize()` produces,
+  through `BasicJsonType`.
 
 ## What is different
 
@@ -167,10 +170,6 @@ 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
@@ -329,14 +328,10 @@ 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:
-
-- **Duplicate keys.** Members looked up by name (`at()`, `value()`, ... and thus the macros) find the **first** member
-  with a repeated key, see [Duplicate keys](#duplicate-keys); `#!cpp materialize().get<T>()` would see the last one.
-  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.
+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);
+`#!cpp materialize().get<T>()` would see the last one. Containers built from an object, such as `#!cpp std::map`,
+keep the **last** value either way, as [`parse()`](../api/basic_json/parse.md) does.
 
 `to_json()` is unaffected: it writes `basic_json` values, never views.