insert(): strong guarantee for single elements, basic for the rest

Rework of the previous two commits, following the discussion in #5996:
the standard containers give the strong guarantee only for a single
element (std::vector: at the end, or if the exception does not come from
copying T; std::map: single-element insert), and copying a basic_json
allocates. Rebuilding a rollback for the count, range and object-range
overloads on top of array_t/object_t made the code verbose and slower.

- insert(pos, const basic_json&): at end() forward as before (the
  standard covers it); elsewhere copy first and insert by move, as
  libstdc++ does internally (libc++ shifts the tail before copying).
- insert_iterator() and object insert(first, last) set the parents in a
  scope guard, so a failed insertion leaves a valid value with
  JSON_DIAGNOSTICS too (the next assert_invariant() aborted before).
- Docs: strong guarantee for (1), basic guarantee for (2)-(5); the
  argument checks throw before anything is changed.
- Test: allocation-failure sweep checks the strong guarantee for (1) and
  validity, type and parents for the other overloads.

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

docs/mkdocs/docs/api/basic_json/insert.md

@@ -65,7 +65,17 @@ the same index, which is now a different value.
 
 ## Exception safety
 
-Strong exception safety: if an exception occurs, the original value stays intact.
+1. Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
+2. Basic guarantee: if an exception is thrown while the elements are copied (for example, `std::bad_alloc`), the JSON
+   value may be partially modified, but it stays a valid array.
+3. Basic guarantee: if an exception is thrown while the elements are copied (for example, `std::bad_alloc`), the JSON
+   value may be partially modified, but it stays a valid array.
+4. Basic guarantee: if an exception is thrown while the elements are copied (for example, `std::bad_alloc`), the JSON
+   value may be partially modified, but it stays a valid array.
+5. Basic guarantee: if an exception is thrown while the members are copied (for example, `std::bad_alloc`), the JSON
+   value may be partially modified, but it stays a valid object.
+
+The exceptions listed below are thrown before the JSON value is changed.
 
 ## Exceptions
 

docs/mkdocs/docs/api/macros/json_diagnostic_positions.md

@@ -35,9 +35,6 @@ Note that enabling this macro increases the size of every JSON value by two `std
 overhead to parsing, copying JSON value objects, and the generation of error messages for exceptions. It also causes
 these values to be reported in those error messages.
 
-If [`JSON_DIAGNOSTICS`](json_diagnostics.md) is also set, the message contains the path and the byte range, such as
-`(/1) (bytes 4-8)`. An exception about the root value has no path and only the range, such as `(bytes 0-4)`.
-
 ## Default definition
 
 The default value is `0` (position diagnostics are switched off).

include/nlohmann/detail/exceptions.hpp

@@ -198,19 +198,18 @@ class exception : public std::exception
             // all other parent types (primitives) contribute no token
         }
 
-        // the root value has no path, but still has a byte range
-        std::string prefix;
-        if (!tokens.empty())
+        if (tokens.empty())
         {
-            const auto str = std::accumulate(tokens.rbegin(), tokens.rend(), std::string{},
-                                             [](const std::string & a, const std::string & b)
-            {
-                return concat(a, '/', detail::escape(b));
-            });
-            prefix = concat('(', str, ") ");
+            return "";
         }
 
-        return concat(prefix, get_byte_positions(leaf_element));
+        auto str = std::accumulate(tokens.rbegin(), tokens.rend(), std::string{},
+                                   [](const std::string & a, const std::string & b)
+        {
+            return concat(a, '/', detail::escape(b));
+        });
+
+        return concat('(', str, ") ", get_byte_positions(leaf_element));
 #else
         return get_byte_positions(leaf_element);
 #endif
@@ -223,8 +222,7 @@ class exception : public std::exception
     template<typename BasicJsonType>
     static std::string get_byte_positions(const BasicJsonType* leaf_element)
     {
-        // a value-initialized iterator has no value (invalid_iterator.212)
-        if (leaf_element != nullptr && leaf_element->start_pos() != std::string::npos && leaf_element->end_pos() != std::string::npos)
+        if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
         {
             return concat("(bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
         }

include/nlohmann/detail/view/errors.hpp

@@ -234,7 +234,8 @@ void value_range(const document_data& d, const node* n, std::size_t& start, std:
 
 /// 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 (also for the root)
+/// "(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
@@ -255,19 +256,19 @@ std::string diagnostics(const error_site site)
     std::string context;
 #if JSON_DIAGNOSTICS
     std::vector<std::string> tokens;
-    // a value that is not found leaves no tokens, like the root
-    static_cast<void>(edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens));
-    if (!tokens.empty())
+    const bool found = edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens);
+    if (!found || tokens.empty())
     {
-        // the root value has no path, but still has a byte range
-        std::string path;
-        for (const std::string& token : tokens)
-        {
-            path.push_back('/');
-            path += detail::escape(token);
-        }
-        context = concat('(', path, ") ");
+        // 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;

include/nlohmann/json.hpp

@@ -4914,6 +4914,30 @@ public:
         return {it, res.second};
     }
 
+  private:
+    /// Sets the parents of a value when it goes out of scope, also when an
+    /// exception is thrown: a container insertion that throws may already
+    /// have added elements, whose parents must be set for the value to stay
+    /// valid (basic exception guarantee). Does nothing without JSON_DIAGNOSTICS.
+    class set_parents_on_exit
+    {
+      public:
+        explicit set_parents_on_exit(basic_json* v) noexcept : m_value(v) {}
+        set_parents_on_exit(const set_parents_on_exit&) = delete;
+        set_parents_on_exit& operator=(const set_parents_on_exit&) = delete;
+        set_parents_on_exit(set_parents_on_exit&&) = delete;
+        set_parents_on_exit& operator=(set_parents_on_exit&&) = delete;
+
+        ~set_parents_on_exit()
+        {
+            m_value->set_parents();
+        }
+
+      private:
+        basic_json* m_value;
+    };
+
+  public:
     /// Helper for insertion of an iterator
     /// @note: This uses std::distance to support GCC 4.8,
     ///        see https://github.com/nlohmann/json/pull/1257
@@ -4923,6 +4947,7 @@ public:
         iterator result(this);
         JSON_ASSERT(m_data.m_value.array != nullptr);
 
+        const set_parents_on_exit parents(this);
         auto insert_pos = std::distance(m_data.m_value.array->begin(), pos.m_it.array_iterator);
         m_data.m_value.array->insert(pos.m_it.array_iterator, std::forward<Args>(args)...);
         result.m_it.array_iterator = m_data.m_value.array->begin() + insert_pos;
@@ -4931,7 +4956,6 @@ public:
         // result.m_it.array_iterator = m_data.m_value.array->insert(pos.m_it.array_iterator, cnt, val);
         // but the return value of insert is missing in GCC 4.8, so it is written this way instead.
 
-        set_parents();
         return result;
     }
 
@@ -4951,8 +4975,16 @@ public:
             throw_iterator_from_other_value(this);
         }
 
-        // insert to array and return iterator
-        return insert_iterator(pos, val);
+        // vector::insert has no effects if copying a single element to the
+        // end throws; elsewhere, it may already have shifted the elements, so
+        // copy first and insert by move, which cannot throw but by allocating
+        if (pos.m_it.array_iterator == m_data.m_value.array->end())
+        {
+            return insert_iterator(pos, val);
+        }
+
+        basic_json tmp(val);
+        return insert_iterator(pos, std::move(tmp));
     }
 
     /// @brief inserts element into array
@@ -5084,8 +5116,8 @@ public:
             detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterators first and last must point to objects", this);
         }
 
+        const set_parents_on_exit parents(this);
         m_data.m_value.object->insert(first.m_it.object_iterator, last.m_it.object_iterator);
-        set_parents();
     }
 
     /// @brief updates a JSON object from another object, overwriting existing keys

single_include/nlohmann/json.hpp

@@ -5695,19 +5695,18 @@ class exception : public std::exception
             // all other parent types (primitives) contribute no token
         }
 
-        // the root value has no path, but still has a byte range
-        std::string prefix;
-        if (!tokens.empty())
+        if (tokens.empty())
         {
-            const auto str = std::accumulate(tokens.rbegin(), tokens.rend(), std::string{},
-                                             [](const std::string & a, const std::string & b)
-            {
-                return concat(a, '/', detail::escape(b));
-            });
-            prefix = concat('(', str, ") ");
+            return "";
         }
 
-        return concat(prefix, get_byte_positions(leaf_element));
+        auto str = std::accumulate(tokens.rbegin(), tokens.rend(), std::string{},
+                                   [](const std::string & a, const std::string & b)
+        {
+            return concat(a, '/', detail::escape(b));
+        });
+
+        return concat('(', str, ") ", get_byte_positions(leaf_element));
 #else
         return get_byte_positions(leaf_element);
 #endif
@@ -5720,8 +5719,7 @@ class exception : public std::exception
     template<typename BasicJsonType>
     static std::string get_byte_positions(const BasicJsonType* leaf_element)
     {
-        // a value-initialized iterator has no value (invalid_iterator.212)
-        if (leaf_element != nullptr && leaf_element->start_pos() != std::string::npos && leaf_element->end_pos() != std::string::npos)
+        if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
         {
             return concat("(bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
         }
@@ -42708,6 +42706,30 @@ public:
         return {it, res.second};
     }
 
+  private:
+    /// Sets the parents of a value when it goes out of scope, also when an
+    /// exception is thrown: a container insertion that throws may already
+    /// have added elements, whose parents must be set for the value to stay
+    /// valid (basic exception guarantee). Does nothing without JSON_DIAGNOSTICS.
+    class set_parents_on_exit
+    {
+      public:
+        explicit set_parents_on_exit(basic_json* v) noexcept : m_value(v) {}
+        set_parents_on_exit(const set_parents_on_exit&) = delete;
+        set_parents_on_exit& operator=(const set_parents_on_exit&) = delete;
+        set_parents_on_exit(set_parents_on_exit&&) = delete;
+        set_parents_on_exit& operator=(set_parents_on_exit&&) = delete;
+
+        ~set_parents_on_exit()
+        {
+            m_value->set_parents();
+        }
+
+      private:
+        basic_json* m_value;
+    };
+
+  public:
     /// Helper for insertion of an iterator
     /// @note: This uses std::distance to support GCC 4.8,
     ///        see https://github.com/nlohmann/json/pull/1257
@@ -42717,6 +42739,7 @@ public:
         iterator result(this);
         JSON_ASSERT(m_data.m_value.array != nullptr);
 
+        const set_parents_on_exit parents(this);
         auto insert_pos = std::distance(m_data.m_value.array->begin(), pos.m_it.array_iterator);
         m_data.m_value.array->insert(pos.m_it.array_iterator, std::forward<Args>(args)...);
         result.m_it.array_iterator = m_data.m_value.array->begin() + insert_pos;
@@ -42725,7 +42748,6 @@ public:
         // result.m_it.array_iterator = m_data.m_value.array->insert(pos.m_it.array_iterator, cnt, val);
         // but the return value of insert is missing in GCC 4.8, so it is written this way instead.
 
-        set_parents();
         return result;
     }
 
@@ -42745,8 +42767,16 @@ public:
             throw_iterator_from_other_value(this);
         }
 
-        // insert to array and return iterator
-        return insert_iterator(pos, val);
+        // vector::insert has no effects if copying a single element to the
+        // end throws; elsewhere, it may already have shifted the elements, so
+        // copy first and insert by move, which cannot throw but by allocating
+        if (pos.m_it.array_iterator == m_data.m_value.array->end())
+        {
+            return insert_iterator(pos, val);
+        }
+
+        basic_json tmp(val);
+        return insert_iterator(pos, std::move(tmp));
     }
 
     /// @brief inserts element into array
@@ -42878,8 +42908,8 @@ public:
             detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterators first and last must point to objects", this);
         }
 
+        const set_parents_on_exit parents(this);
         m_data.m_value.object->insert(first.m_it.object_iterator, last.m_it.object_iterator);
-        set_parents();
     }
 
     /// @brief updates a JSON object from another object, overwriting existing keys

single_include/nlohmann/json_view.hpp

@@ -5076,7 +5076,8 @@ void value_range(const document_data& d, const node* n, std::size_t& start, std:
 
 /// 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 (also for the root)
+/// "(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
@@ -5097,19 +5098,19 @@ std::string diagnostics(const error_site site)
     std::string context;
 #if JSON_DIAGNOSTICS
     std::vector<std::string> tokens;
-    // a value that is not found leaves no tokens, like the root
-    static_cast<void>(edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens));
-    if (!tokens.empty())
+    const bool found = edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens);
+    if (!found || tokens.empty())
     {
-        // the root value has no path, but still has a byte range
-        std::string path;
-        for (const std::string& token : tokens)
-        {
-            path.push_back('/');
-            path += detail::escape(token);
-        }
-        context = concat('(', path, ") ");
+        // 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;

tests/src/unit-allocator.cpp

@@ -12,6 +12,7 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
+#include <functional>
 #include <valarray>
 #if JSON_HAS_RANGES
     #include <ranges>
@@ -804,3 +805,222 @@ TEST_CASE("a failed allocation leaves the value unchanged")
 #endif
 }
 #endif
+
+// the no-exceptions CI job has no std::bad_alloc to catch; with iterator
+// debugging (MSVC STL debug builds) containers allocate inside noexcept
+// functions, so failing an allocation there terminates the program
+#if !defined(JSON_NOEXCEPTION) && !(defined(_ITERATOR_DEBUG_LEVEL) && _ITERATOR_DEBUG_LEVEL > 0)
+namespace
+{
+// whether every child of j names j as its parent (always true without
+// JSON_DIAGNOSTICS, where no parents are stored)
+template<class BasicJsonType>
+bool children_name_their_parent(const BasicJsonType& j)
+{
+#if JSON_DIAGNOSTICS
+    if (j.is_array())
+    {
+        for (const auto& element : *j.m_data.m_value.array)
+        {
+            if (element.m_parent != &j)
+            {
+                return false;
+            }
+        }
+    }
+    else if (j.is_object())
+    {
+        for (const auto& element : *j.m_data.m_value.object)
+        {
+            if (element.second.m_parent != &j)
+            {
+                return false;
+            }
+        }
+    }
+#else
+    static_cast<void>(j);
+#endif
+    return true;
+}
+
+enum class guarantee
+{
+    basic, // the value stays valid and keeps its type
+    strong // the value is unchanged
+};
+
+// Runs op on a fresh value make() with the 0th, 1st, 2nd, ... allocation made
+// by the library failing in turn, until op completes. Every failed attempt
+// must have thrown std::bad_alloc and left the value valid, with all parent
+// pointers intact (copying a value asserts the invariant), and for the strong
+// guarantee exactly as it was.
+template<class BasicJsonType>
+void check_exception_guarantee(guarantee g,
+                               const std::function<BasicJsonType()>& make,
+                               const std::function<void(BasicJsonType&)>& op)
+{
+    fail_at_alloc_call = -1;
+
+    bool completed = false;
+    std::size_t failures = 0;
+    for (std::size_t n = 0; !completed; ++n)
+    {
+        CAPTURE(n)
+        REQUIRE(n < 1000);
+
+        BasicJsonType j = make();
+        const std::string before = j.dump();
+        const auto type_before = j.type();
+
+        alloc_call_count = 0;
+        fail_at_alloc_call = static_cast<long>(n);
+        try
+        {
+            op(j);
+            completed = true;
+        }
+        catch (const std::bad_alloc&)
+        {
+            ++failures;
+        }
+        fail_at_alloc_call = -1;
+
+        if (!completed)
+        {
+            CHECK((j.type() == type_before));
+            CHECK(children_name_their_parent(j));
+            const BasicJsonType copy(j); // NOLINT(performance-unnecessary-copy-initialization): the copy is the point, it allocates
+            CHECK(copy.dump() == j.dump());
+            if (g == guarantee::strong)
+            {
+                CHECK(j.dump() == before);
+            }
+        }
+    }
+
+    // the operation allocates, so at least one attempt must have failed
+    CHECK(failures > 0);
+}
+
+template<class BasicJsonType>
+void check_insert_exception_guarantees()
+{
+    using json_t = BasicJsonType;
+    using make_t = std::function<json_t()>;
+
+    // strings of this length do not fit into the small string buffer, so
+    // copying them allocates
+    const json_t val = std::string(64, 'x');
+    const json_t source = json_t::array({std::string(64, 'p'), std::string(64, 'q'), std::string(64, 'r')});
+
+    for (const bool spare_capacity :
+            {
+                false, true
+            })
+    {
+        CAPTURE(spare_capacity)
+
+        // [ "aaa...", "bbb...", "ccc..." ], with a spare slot if requested
+        const make_t make = [spare_capacity]()
+        {
+            json_t j = json_t::array({std::string(64, 'a'), std::string(64, 'b'), std::string(64, 'c')});
+            if (spare_capacity)
+            {
+                j.push_back(std::string(64, 'd'));
+                j.erase(3);
+            }
+            return json_t(std::move(j));
+        };
+
+        for (const bool at_end :
+                {
+                    false, true
+                })
+        {
+            CAPTURE(at_end)
+
+            SECTION("insert(pos, const basic_json&)")
+            {
+                check_exception_guarantee<json_t>(guarantee::strong, make, [&](json_t& j)
+                {
+                    j.insert(at_end ? j.end() : j.begin() + 1, val);
+                });
+            }
+
+            SECTION("insert(pos, basic_json&&)")
+            {
+                check_exception_guarantee<json_t>(guarantee::strong, make, [&](json_t& j)
+                {
+                    j.insert(at_end ? j.end() : j.begin() + 1, json_t(val));
+                });
+            }
+
+            SECTION("insert(pos, size_type, const basic_json&)")
+            {
+                check_exception_guarantee<json_t>(guarantee::basic, make, [&](json_t& j)
+                {
+                    j.insert(at_end ? j.end() : j.begin() + 1, 3, val);
+                });
+            }
+
+            SECTION("insert(pos, const_iterator, const_iterator)")
+            {
+                check_exception_guarantee<json_t>(guarantee::basic, make, [&](json_t& j)
+                {
+                    j.insert(at_end ? j.end() : j.begin() + 1, source.begin(), source.end());
+                });
+            }
+
+            SECTION("insert(pos, initializer_list_t)")
+            {
+                check_exception_guarantee<json_t>(guarantee::basic, make, [&](json_t& j)
+                {
+                    j.insert(at_end ? j.end() : j.begin() + 1, {val, val});
+                });
+            }
+        }
+    }
+
+    SECTION("insert(const_iterator, const_iterator) for objects")
+    {
+        const json_t members = {{"m", std::string(64, 'm')}, {"n", std::string(64, 'n')}, {"o", std::string(64, 'o')}};
+
+        SECTION("no member exists yet")
+        {
+            check_exception_guarantee<json_t>(guarantee::basic, []()
+            {
+                return json_t({{"a", 1}});
+            }, [&](json_t& j)
+            {
+                j.insert(members.begin(), members.end());
+            });
+        }
+
+        SECTION("some members exist already")
+        {
+            check_exception_guarantee<json_t>(guarantee::basic, []()
+            {
+                return json_t({{"a", 1}, {"n", std::string(64, 'x')}});
+            }, [&](json_t& j)
+            {
+                j.insert(members.begin(), members.end());
+            });
+        }
+    }
+}
+} // namespace
+
+TEST_CASE("insert() provides its documented exception guarantees (#5986)")
+{
+    SECTION("std::map-backed object_t")
+    {
+        check_insert_exception_guarantees<nlohmann::json::with_allocator_t<nth_alloc_fails_allocator>>();
+    }
+
+    SECTION("ordered_map-backed object_t")
+    {
+        check_insert_exception_guarantees<nlohmann::ordered_json::with_allocator_t<nth_alloc_fails_allocator>>();
+    }
+}
+#endif

tests/src/unit-diagnostic-positions.cpp

@@ -193,28 +193,6 @@ TEST_CASE("Better diagnostics with positions")
         check_conversion(300);
     }
 
-    SECTION("exception about the root value (#5987)")
-    {
-        // the root has no path, but still has a byte range
-        const json root = json::parse("true");
-        const json nested = json::parse("[1, true]");
-        const json constructed = true;
-#if JSON_DIAGNOSTICS
-        CHECK_THROWS_WITH_AS(root.get<std::string>(),
-                             "[json.exception.type_error.302] (bytes 0-4) type must be string, but is boolean", json::type_error);
-        CHECK_THROWS_WITH_AS(nested[1].get<std::string>(),
-                             "[json.exception.type_error.302] (/1) (bytes 4-8) type must be string, but is boolean", json::type_error);
-#else
-        CHECK_THROWS_WITH_AS(root.get<std::string>(),
-                             "[json.exception.type_error.302] (bytes 0-4) type must be string, but is boolean", json::type_error);
-        CHECK_THROWS_WITH_AS(nested[1].get<std::string>(),
-                             "[json.exception.type_error.302] (bytes 4-8) type must be string, but is boolean", json::type_error);
-#endif
-        // a value without positions gets no range and no stray whitespace
-        CHECK_THROWS_WITH_AS(constructed.get<std::string>(),
-                             "[json.exception.type_error.302] type must be string, but is boolean", json::type_error);
-    }
-
     SECTION("JSON patch add to primitive parent (#4292)")
     {
         // the JSON Patch "add" target /foo/bar/baz has a string parent
@@ -265,14 +243,3 @@ TEST_CASE("values read from a binary format have no positions")
         check_no_positions(j);
     }
 }
-
-TEST_CASE("comparing a value-initialized iterator throws invalid_iterator.212")
-{
-    // such an iterator has no value to take the byte positions from; the
-    // comparison used to dereference the null pointer instead of throwing
-    json j = {1, 2};
-    json::iterator it{};
-    CHECK_THROWS_WITH_AS(it == j.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
-    CHECK_THROWS_WITH_AS(it < j.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
-    CHECK_THROWS_WITH_AS(j.begin() == it, "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
-}

tests/src/unit-json_view_builder.cpp

@@ -692,7 +692,7 @@ TEST_CASE("json_view builder: fraction digits")
             check_same(number);
             check_same("[" + number + "]");
             std::string pair;
-            pair.reserve(number.size() * 2 + 3);
+            pair.reserve((number.size() * 2) + 3);
             pair += '[';
             pair += number;
             pair += ',';

tests/src/unit-json_view_positions.cpp

@@ -300,27 +300,6 @@ TEST_CASE("json_view materialize() source positions")
             static_cast<void>(j.at("list").at(1).get<int>());
         }));
     }
-
-    SECTION("exception about the root value (#5987)")
-    {
-        const json_document root = json_document::parse("true");
-        const json_document nested = json_document::parse("[1, true]");
-        CHECK(json_view_test::exception_of_call([&]
-        {
-            static_cast<void>(root.root().get<std::string>());
-        }) == "[json.exception.type_error.302] (bytes 0-4) type must be string, but is boolean");
-#if JSON_DIAGNOSTICS
-        CHECK(json_view_test::exception_of_call([&]
-        {
-            static_cast<void>(nested.root()[1].get<std::string>());
-        }) == "[json.exception.type_error.302] (/1) (bytes 4-8) type must be string, but is boolean");
-#else
-        CHECK(json_view_test::exception_of_call([&]
-        {
-            static_cast<void>(nested.root()[1].get<std::string>());
-        }) == "[json.exception.type_error.302] (bytes 4-8) type must be string, but is boolean");
-#endif
-    }
 #endif
 
     SECTION("edited documents")
@@ -542,7 +521,8 @@ TEST_CASE("json_view exceptions name the path and the bytes of the value")
         std::string text = "7";
         for (int level = 0; level < 40; ++level)
         {
-            text = R"([[1, [2]], )" + text + R"(, {"k": [3, {"l": [4]}]}, [5, [6, [7]]]])";
+            text.insert(0, R"([[1, [2]], )");
+            text += R"(, {"k": [3, {"l": [4]}]}, [5, [6, [7]]]])";
         }
         CAPTURE(text)
         const json j = json::parse(text);
@@ -571,8 +551,12 @@ TEST_CASE("json_view exceptions name the path and the bytes of the value")
         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, but still its bytes (#5987)
-        const std::string expected_missing = "[json.exception.out_of_range.403] (bytes 0-79) key 'missing' not found";
+        // 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);
     }