Construct a scalar member in place; only a throwing value goes through a temporary

Creating the value first and moving it over the member is needed only when
creating it can throw (a string, a binary value or a container). A scalar
or null is again constructed in place, without the extra move and destroy
per member (and, with JSON_DIAGNOSTICS, without the extra set_parents()).

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

.github/workflows/cancel_closed_pr_runs.yml

@@ -24,7 +24,7 @@ jobs:
     permissions:
       actions: write
 
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
 
     steps:
       - name: Harden Runner

.github/workflows/check_amalgamation.yml

@@ -19,7 +19,7 @@ permissions:
 jobs:
   save:
     if: github.event_name == 'pull_request'
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
         uses: step-security/harden-runner@dc2769abcc0fcfbadfc1df54081c1608579ef6b2 # v2.22.2

.github/workflows/check_docs_links.yml

@@ -16,7 +16,7 @@ concurrency:
 jobs:
   check_docs_links:
     if: github.repository == 'nlohmann/json'
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     timeout-minutes: 30
     steps:
       - name: Harden Runner

.github/workflows/comment_check_amalgamation.yml

@@ -12,7 +12,7 @@ jobs:
   comment:
     # push runs on develop have no PR to comment on (and no "pr" artifact)
     if: ${{ github.event.workflow_run.conclusion == 'failure' && github.event.workflow_run.event == 'pull_request' }}
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     permissions:
       contents: read
       actions: read

.github/workflows/dependency-review.yml

@@ -18,7 +18,7 @@ permissions:
 
 jobs:
   dependency-review:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
         uses: step-security/harden-runner@dc2769abcc0fcfbadfc1df54081c1608579ef6b2 # v2.22.2

.github/workflows/flawfinder.yml

@@ -24,7 +24,7 @@ on:
 jobs:
   flawfinder:
     name: Flawfinder
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     permissions:
       actions: read
       contents: read

.github/workflows/labeler.yml

@@ -19,7 +19,7 @@ jobs:
       contents: read
       pull-requests: write
 
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
 
     steps:
       - name: Harden Runner

.github/workflows/publish_documentation.yml

@@ -34,7 +34,7 @@ jobs:
       contents: write
 
     if: github.repository == 'nlohmann/json'
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
         uses: step-security/harden-runner@dc2769abcc0fcfbadfc1df54081c1608579ef6b2 # v2.22.2

.github/workflows/scorecards.yml

@@ -24,7 +24,7 @@ permissions:
 jobs:
   analysis:
     name: Scorecard analysis
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     permissions:
       # Needed to upload the results to code-scanning dashboard.
       security-events: write

.github/workflows/stale.yml

@@ -8,7 +8,7 @@ permissions:
 
 jobs:
   stale:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
 
     permissions:
       issues: write

.github/workflows/ubuntu.yml

@@ -18,7 +18,7 @@ concurrency:
 
 jobs:
   ci_test_gcc:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     container: gcc:latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -130,7 +130,7 @@ jobs:
         run: cmake --build build --target ${{ matrix.target }}
 
   ci_static_analysis_clang:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     container: silkeh/clang:22
     strategy:
       matrix:
@@ -149,7 +149,7 @@ jobs:
         run: cmake --build build --target ${{ matrix.target }}
 
   ci_cmake_options:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     container: ubuntu:24.04
     strategy:
       matrix:
@@ -209,7 +209,7 @@ jobs:
           fail-on-error: false
 
   ci_test_compilers_gcc_old:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         compiler: ['4.8', '4.9', '5', '6']
@@ -251,7 +251,7 @@ jobs:
         run: cmake --build build --target ci_test_compiler_g++-${{ matrix.compiler }}
 
   ci_test_compilers_gcc:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         # older GCC docker images (4, 5, 6) fail to check out code
@@ -269,7 +269,7 @@ jobs:
         run: cmake --build build --target ci_test_compiler_default
 
   ci_test_compilers_clang:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         compiler: ['3.4', '3.5', '3.6', '3.7', '3.8', '3.9', '4', '5', '6', '7', '8', '9', '10', '11', '12', '13', '14', '15-bullseye', '16', '17', '18', '19', '20', '21', '22', 'latest']
@@ -289,7 +289,7 @@ jobs:
         run: cmake --build build --target ci_test_compiler_default
 
   ci_test_standards_gcc:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     container: gcc:latest
     strategy:
       matrix:
@@ -306,7 +306,7 @@ jobs:
         run: cmake --build build --target ci_test_gcc_cxx${{ matrix.standard }}
 
   ci_test_standards_clang:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     container: silkeh/clang:latest
     strategy:
       matrix:
@@ -330,7 +330,7 @@ jobs:
         if: ${{ matrix.stdlib == 'libstdcxx' }}
 
   ci_cuda_example:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
@@ -356,7 +356,7 @@ jobs:
     strategy:
       matrix:
         container: ['gcc:latest', 'silkeh/clang:latest']
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     container: ${{ matrix.container }}
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -383,7 +383,7 @@ jobs:
         run: cmake --build build --target ci_module_cpp20
 
   ci_icpc:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     # Intel discontinued the classic icc/icpc compiler in oneAPI 2024.0; this is
     # Intel's own last officially published image that still includes it.
     container: intel/oneapi-hpckit:2023.2.1-devel-ubuntu22.04
@@ -402,7 +402,7 @@ jobs:
         run: cmake --build build --target ci_icpc
 
   ci_icpx:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     container: intel/oneapi-hpckit:latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -416,7 +416,7 @@ jobs:
         run: cmake --build build --target ci_icpx
 
   ci_nvhpc:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-latest
     container: nvcr.io/nvidia/nvhpc:25.5-devel-cuda12.9-ubuntu22.04
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1

include/nlohmann/detail/input/binary_reader.hpp

@@ -467,13 +467,11 @@ 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, and only
+            // and those names are not passed on: they are skipped unless
-            // checked if error_handler_t::strict must reject ill-formed UTF-8
+            // 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(!(is_object || error_handler != error_handler_t::strict
+            if (JSON_HEDLEY_UNLIKELY(!get_bson_cstr(key, is_object || error_handler == error_handler_t::strict)))
-                                       ? get_bson_cstr(key, is_object)
-                                       : check_bson_cstr(key, std::integral_constant<bool, bulk_scan> {}))))
             {
                 return false;
             }
@@ -497,7 +495,7 @@ class binary_reader
     @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 (@ref check_bson_cstr checks them)
+                      @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.
     */
@@ -556,42 +554,6 @@ class binary_reader
         return true;
     }
 
-    /*!
-    @brief skip a C-style string that error_handler_t::strict must check
-
-    The names of an array's elements are not passed on. On contiguous input,
-    a well-formed name is checked in place and skipped without being copied.
-    Otherwise (no \\x00-byte in the input that can be scanned, or ill-formed
-    UTF-8), it is read by @ref get_bson_cstr, which reports the error.
-
-    @param[in,out] result  an empty string, which may receive the name
-    @return whether the name was read and is well-formed
-    */
-    bool check_bson_cstr(string_t& result, std::true_type /*bulk*/)
-    {
-        const std::size_t remaining = ia.bulk_remaining();
-        if (remaining != 0)
-        {
-            const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
-            const std::size_t length = find_zero_byte(data, remaining);
-            if (length != remaining && JSON_HEDLEY_LIKELY(valid_utf8_string(data, length)))
-            {
-                // consume the string and its \x00-byte, as get_bson_cstr does
-                ia.bulk_skip(length + 1);
-                chars_read += length + 1;
-                current = 0x00;
-                return true;
-            }
-        }
-        return get_bson_cstr(result);
-    }
-
-    /// input that is not contiguous: the name is read and checked byte by byte
-    bool check_bson_cstr(string_t& result, std::false_type /*bulk*/)
-    {
-        return get_bson_cstr(result);
-    }
-
     /// input that is not contiguous: C-style strings are read byte by byte
     bool get_bson_cstr_bulk(string_t& /*result*/, const bool /*store*/, std::false_type /*bulk*/) const noexcept
     {

include/nlohmann/detail/input/json_sax.hpp

@@ -1303,7 +1303,7 @@ class json_sax_dom_parser : public json_sax_dom_error_state
         {
             // a new member is null and holds nothing: construct the value
             // over it instead of destroying and swapping
-            ::new (static_cast<void*>(&member)) BasicJsonType(std::forward<Value>(v));
+            construct_member(member, std::forward<Value>(v), std::is_nothrow_constructible < BasicJsonType, Value && > {});
         }
         else
         {
@@ -1312,6 +1312,25 @@ class json_sax_dom_parser : public json_sax_dom_error_state
         }
     }
 
+    /// a scalar cannot throw: construct it in place
+    template<typename Value>
+    JSON_HEDLEY_ALWAYS_INLINE
+    static void construct_member(BasicJsonType& member, Value&& v, std::true_type /*nothrow*/)
+    {
+        ::new (static_cast<void*>(&member)) BasicJsonType(std::forward<Value>(v));
+    }
+
+    /// creating a container or a string can throw, and a constructor that was
+    /// interrupted must not have touched the member (#5985): create the value
+    /// first, then move it over the member (the move constructor is noexcept)
+    template<typename Value>
+    JSON_HEDLEY_ALWAYS_INLINE
+    static void construct_member(BasicJsonType& member, Value&& v, std::false_type /*may throw*/)
+    {
+        BasicJsonType value(std::forward<Value>(v));
+        ::new (static_cast<void*>(&member)) BasicJsonType(std::move(value));
+    }
+
     /// a custom base class may care about the lifetime of the value
     template<typename Value>
     static void set_member(BasicJsonType& member, Value&& v, std::false_type /*custom base*/)

include/nlohmann/json.hpp

@@ -543,10 +543,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     ////////////////////////
 
   JSON_PRIVATE_UNLESS_TESTED:
-    // the type and value of a basic_json without its base class (defined
-    // below); the destruction helpers of json_value use it as a stand-in
-    struct data;
-
     /*!
     @brief a JSON value
 
@@ -723,28 +719,27 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         explicit json_value(array_t* value) noexcept : array(value) {}
 
 private:
-        // raw, allocation-free transfer of the type and value from src to
+        // raw, allocation-free transfer of m_data from src to dst: no
-        // dst: no set_parents()/assert_invariant() (the former is
+        // set_parents()/assert_invariant() (the former is O(#children) per
-        // O(#children) per call under JSON_DIAGNOSTICS, which would make the
+        // call under JSON_DIAGNOSTICS, which would make the walk below
-        // walk below quadratic); dst takes ownership, src is left as
+        // quadratic); dst takes ownership, src is left as value_t::null.
-        // value_t::null.
+        static void take(basic_json& dst, basic_json& src) noexcept
-        static void take(data& dst, data& src) noexcept
         {
-            dst.m_type = src.m_type;
+            dst.m_data.m_type = src.m_data.m_type;
-            dst.m_value = src.m_value;
+            dst.m_data.m_value = src.m_data.m_value;
-            src.m_type = value_t::null;
+            src.m_data.m_type = value_t::null;
         }
 
         // true if v is not an array/object, or is an already-empty one
-        static bool has_no_children(const data& v) noexcept
+        static bool has_no_children(const basic_json& v) noexcept
         {
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                return v.m_value.array->empty();
+                return v.m_data.m_value.array->empty();
             }
-            if (v.m_type == value_t::object)
+            if (v.m_data.m_type == value_t::object)
             {
-                return v.m_value.object->empty();
+                return v.m_data.m_value.object->empty();
             }
             return true;
         }
@@ -753,21 +748,21 @@ private:
         // its own, i.e. v can be freed in one go (its destructor then
         // destroys scalars and empty containers only, so it recurses at most
         // one level deep); stops at the first structured child it meets
-        static bool all_children_leaves(const data& v) noexcept
+        static bool all_children_leaves(const basic_json& v) noexcept
         {
             // array_t only needs forward iterators (see custom_array_type)
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                const auto& a = *v.m_value.array;
+                const auto& a = *v.m_data.m_value.array;
                 return std::all_of(a.begin(), a.end(), [](const basic_json & el)
                 {
-                    return has_no_children(el.m_data);
+                    return has_no_children(el);
                 });
             }
-            const auto& o = *v.m_value.object;
+            const auto& o = *v.m_data.m_value.object;
             return std::all_of(o.begin(), o.end(), [](const typename object_t::value_type & el)
             {
-                return has_no_children(el.second.m_data);
+                return has_no_children(el.second);
             });
         }
 
@@ -799,30 +794,30 @@ private:
 
         // the child of a non-empty array/object v that the walk in
         // destroy_container() continues with (see walk_child_it() above)
-        static data& walk_child(data& v)
+        static basic_json& walk_child(basic_json& v)
         {
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                return v.m_value.array->back().m_data;
+                return v.m_data.m_value.array->back();
             }
-            JSON_ASSERT(v.m_type == value_t::object);
+            JSON_ASSERT(v.m_data.m_type == value_t::object);
-            return walk_child_it(*v.m_value.object)->second.m_data;
+            return walk_child_it(*v.m_data.m_value.object)->second;
         }
 
         // removes walk_child(v) from a non-empty array/object v; this never
         // allocates, and since it is only ever called when that child is a
         // scalar or an already-empty array/object, destroying it never
         // recurses more than one level deep (see destroy() below)
-        static void pop_walk_child(data& v)
+        static void pop_walk_child(basic_json& v)
         {
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                v.m_value.array->pop_back();
+                v.m_data.m_value.array->pop_back();
             }
             else
             {
-                JSON_ASSERT(v.m_type == value_t::object);
+                JSON_ASSERT(v.m_data.m_type == value_t::object);
-                v.m_value.object->erase(walk_child_it(*v.m_value.object));
+                v.m_data.m_value.object->erase(walk_child_it(*v.m_data.m_value.object));
             }
         }
 
@@ -831,23 +826,23 @@ private:
         // recurses at most one level deep); this is the same allocator-based
         // free the old recursive implementation used, just factored out so
         // every level of the walk in destroy() can share it
-        static void free_container(data& v) noexcept
+        static void free_container(basic_json& v) noexcept
         {
             JSON_ASSERT(has_no_children(v) || all_children_leaves(v));
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
                 AllocatorType<array_t> alloc;
-                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_value.array);
+                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_data.m_value.array);
-                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_value.array, 1);
+                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_data.m_value.array, 1);
             }
             else
             {
-                JSON_ASSERT(v.m_type == value_t::object);
+                JSON_ASSERT(v.m_data.m_type == value_t::object);
                 AllocatorType<object_t> alloc;
-                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_value.object);
+                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_data.m_value.object);
-                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_value.object, 1);
+                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_data.m_value.object, 1);
             }
-            v.m_type = value_t::null; // avoid a double free if v is later destructed
+            v.m_data.m_type = value_t::null; // avoid a double free if v is later destructed
         }
 
 public:
@@ -878,16 +873,14 @@ public:
 
             // This json_value is not itself a basic_json, so the top-level
             // container is first moved into a local stand-in ("cur"); a
-            // default-constructed data has a null pointer in its m_value
+            // default-constructed basic_json has a null pointer in its
-            // (see data::m_value's initializer), so swapping it with *this
+            // m_value (see data::m_value's initializer), so swapping it
-            // leaves this union's own pointer null, and it is never looked
+            // with *this leaves this union's own pointer null, and it is
-            // at or freed a second time. The stand-ins are data, not
+            // never looked at or freed a second time.
-            // basic_json, so that destroying a value never constructs a
+            basic_json cur;
-            // CustomBaseClass, whose constructor may allocate (#5995).
+            cur.m_data.m_type = t;
-            data cur;
-            cur.m_type = t;
             using std::swap;
-            swap(cur.m_value, *this);
+            swap(cur.m_data.m_value, *this);
 
             destroy_bounded(cur, 0);
         }
@@ -896,7 +889,7 @@ public:
         // The first recursion_depth_limit() levels are destroyed by plain
         // recursion, which is the fastest way and cannot throw; anything
         // nested deeper is handed to destroy_walk(), which uses no call stack.
-        static void destroy_bounded(data& v, std::size_t depth) noexcept
+        static void destroy_bounded(basic_json& v, std::size_t depth) noexcept
         {
             if (JSON_HEDLEY_UNLIKELY(depth >= detail::recursion_depth_limit()))
             {
@@ -904,23 +897,23 @@ public:
                 return;
             }
 
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                for (auto& child : *v.m_value.array)
+                for (auto& child : *v.m_data.m_value.array)
                 {
                     if (child.m_data.m_type == value_t::array || child.m_data.m_type == value_t::object)
                     {
-                        destroy_bounded(child.m_data, depth + 1);
+                        destroy_bounded(child, depth + 1);
                     }
                 }
             }
             else
             {
-                for (auto& child : *v.m_value.object)
+                for (auto& child : *v.m_data.m_value.object)
                 {
                     if (child.second.m_data.m_type == value_t::array || child.second.m_data.m_type == value_t::object)
                     {
-                        destroy_bounded(child.second.m_data, depth + 1);
+                        destroy_bounded(child.second, depth + 1);
                     }
                 }
             }
@@ -947,15 +940,18 @@ public:
         // array/object, which neither allocates nor recurses more
         // than one level deep.
         //
-        // Like destroy_container(), the walk keeps the containers it
+        // This json_value is not itself a basic_json, so the
-        // holds in data stand-ins (cur, prev, gp, tmp), which never
+        // top-level container is first moved into a local stand-in
-        // construct a CustomBaseClass.
+        // ("cur"); a default-constructed basic_json has a null
-        static void destroy_walk(data& top) noexcept
+        // pointer in its m_value (see data::m_value's initializer),
+        // so swapping it with *this leaves this union's own pointer
+        // null, and it is never looked at or freed a second time.
+        static void destroy_walk(basic_json& top) noexcept
         {
-            data cur;
+            basic_json cur;
             take(cur, top);
 
-            data prev; // value_t::null: no parent
+            basic_json prev; // value_t::null: no parent
 
             // true right after cur was entered: its children have not been
             // looked at yet. If none of them has children of its own, cur is
@@ -969,7 +965,7 @@ public:
                 fresh = false;
                 if (has_no_children(cur) || (fresh_now && all_children_leaves(cur)))
                 {
-                    if (prev.m_type == value_t::null)
+                    if (prev.m_data.m_type == value_t::null)
                     {
                         free_container(cur);
                         return; // back at the top with nothing left to do
@@ -978,7 +974,7 @@ public:
                     // ascend: detach the grandparent link from prev's
                     // walk_child() slot, drop that (now null) slot, free cur
                     // (it is empty), then move up one level
-                    data gp;
+                    basic_json gp;
                     take(gp, walk_child(prev));
                     pop_walk_child(prev);
 
@@ -989,7 +985,7 @@ public:
                     continue;
                 }
 
-                data& cur_child_ref = walk_child(cur);
+                basic_json& cur_child_ref = walk_child(cur);
 
                 if (has_no_children(cur_child_ref))
                 {
@@ -1001,7 +997,7 @@ public:
                 // descend into the non-empty child, reversing the
                 // link: its slot takes over prev, and the child becomes
                 // the new cur
-                data tmp;
+                basic_json tmp;
                 take(tmp, cur_child_ref);
                 take(cur_child_ref, prev);
                 take(prev, cur);

single_include/nlohmann/json.hpp

@@ -16948,7 +16948,7 @@ class json_sax_dom_parser : public json_sax_dom_error_state
         {
             // a new member is null and holds nothing: construct the value
             // over it instead of destroying and swapping
-            ::new (static_cast<void*>(&member)) BasicJsonType(std::forward<Value>(v));
+            construct_member(member, std::forward<Value>(v), std::is_nothrow_constructible < BasicJsonType, Value && > {});
         }
         else
         {
@@ -16957,6 +16957,25 @@ class json_sax_dom_parser : public json_sax_dom_error_state
         }
     }
 
+    /// a scalar cannot throw: construct it in place
+    template<typename Value>
+    JSON_HEDLEY_ALWAYS_INLINE
+    static void construct_member(BasicJsonType& member, Value&& v, std::true_type /*nothrow*/)
+    {
+        ::new (static_cast<void*>(&member)) BasicJsonType(std::forward<Value>(v));
+    }
+
+    /// creating a container or a string can throw, and a constructor that was
+    /// interrupted must not have touched the member (#5985): create the value
+    /// first, then move it over the member (the move constructor is noexcept)
+    template<typename Value>
+    JSON_HEDLEY_ALWAYS_INLINE
+    static void construct_member(BasicJsonType& member, Value&& v, std::false_type /*may throw*/)
+    {
+        BasicJsonType value(std::forward<Value>(v));
+        ::new (static_cast<void*>(&member)) BasicJsonType(std::move(value));
+    }
+
     /// a custom base class may care about the lifetime of the value
     template<typename Value>
     static void set_member(BasicJsonType& member, Value&& v, std::false_type /*custom base*/)
@@ -18474,13 +18493,11 @@ 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, and only
+            // and those names are not passed on: they are skipped unless
-            // checked if error_handler_t::strict must reject ill-formed UTF-8
+            // 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(!(is_object || error_handler != error_handler_t::strict
+            if (JSON_HEDLEY_UNLIKELY(!get_bson_cstr(key, is_object || error_handler == error_handler_t::strict)))
-                                       ? get_bson_cstr(key, is_object)
-                                       : check_bson_cstr(key, std::integral_constant<bool, bulk_scan> {}))))
             {
                 return false;
             }
@@ -18504,7 +18521,7 @@ class binary_reader
     @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 (@ref check_bson_cstr checks them)
+                      @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.
     */
@@ -18563,42 +18580,6 @@ class binary_reader
         return true;
     }
 
-    /*!
-    @brief skip a C-style string that error_handler_t::strict must check
-
-    The names of an array's elements are not passed on. On contiguous input,
-    a well-formed name is checked in place and skipped without being copied.
-    Otherwise (no \\x00-byte in the input that can be scanned, or ill-formed
-    UTF-8), it is read by @ref get_bson_cstr, which reports the error.
-
-    @param[in,out] result  an empty string, which may receive the name
-    @return whether the name was read and is well-formed
-    */
-    bool check_bson_cstr(string_t& result, std::true_type /*bulk*/)
-    {
-        const std::size_t remaining = ia.bulk_remaining();
-        if (remaining != 0)
-        {
-            const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
-            const std::size_t length = find_zero_byte(data, remaining);
-            if (length != remaining && JSON_HEDLEY_LIKELY(valid_utf8_string(data, length)))
-            {
-                // consume the string and its \x00-byte, as get_bson_cstr does
-                ia.bulk_skip(length + 1);
-                chars_read += length + 1;
-                current = 0x00;
-                return true;
-            }
-        }
-        return get_bson_cstr(result);
-    }
-
-    /// input that is not contiguous: the name is read and checked byte by byte
-    bool check_bson_cstr(string_t& result, std::false_type /*bulk*/)
-    {
-        return get_bson_cstr(result);
-    }
-
     /// input that is not contiguous: C-style strings are read byte by byte
     bool get_bson_cstr_bulk(string_t& /*result*/, const bool /*store*/, std::false_type /*bulk*/) const noexcept
     {
@@ -38373,10 +38354,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     ////////////////////////
 
   JSON_PRIVATE_UNLESS_TESTED:
-    // the type and value of a basic_json without its base class (defined
-    // below); the destruction helpers of json_value use it as a stand-in
-    struct data;
-
     /*!
     @brief a JSON value
 
@@ -38553,28 +38530,27 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         explicit json_value(array_t* value) noexcept : array(value) {}
 
 private:
-        // raw, allocation-free transfer of the type and value from src to
+        // raw, allocation-free transfer of m_data from src to dst: no
-        // dst: no set_parents()/assert_invariant() (the former is
+        // set_parents()/assert_invariant() (the former is O(#children) per
-        // O(#children) per call under JSON_DIAGNOSTICS, which would make the
+        // call under JSON_DIAGNOSTICS, which would make the walk below
-        // walk below quadratic); dst takes ownership, src is left as
+        // quadratic); dst takes ownership, src is left as value_t::null.
-        // value_t::null.
+        static void take(basic_json& dst, basic_json& src) noexcept
-        static void take(data& dst, data& src) noexcept
         {
-            dst.m_type = src.m_type;
+            dst.m_data.m_type = src.m_data.m_type;
-            dst.m_value = src.m_value;
+            dst.m_data.m_value = src.m_data.m_value;
-            src.m_type = value_t::null;
+            src.m_data.m_type = value_t::null;
         }
 
         // true if v is not an array/object, or is an already-empty one
-        static bool has_no_children(const data& v) noexcept
+        static bool has_no_children(const basic_json& v) noexcept
         {
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                return v.m_value.array->empty();
+                return v.m_data.m_value.array->empty();
             }
-            if (v.m_type == value_t::object)
+            if (v.m_data.m_type == value_t::object)
             {
-                return v.m_value.object->empty();
+                return v.m_data.m_value.object->empty();
             }
             return true;
         }
@@ -38583,21 +38559,21 @@ private:
         // its own, i.e. v can be freed in one go (its destructor then
         // destroys scalars and empty containers only, so it recurses at most
         // one level deep); stops at the first structured child it meets
-        static bool all_children_leaves(const data& v) noexcept
+        static bool all_children_leaves(const basic_json& v) noexcept
         {
             // array_t only needs forward iterators (see custom_array_type)
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                const auto& a = *v.m_value.array;
+                const auto& a = *v.m_data.m_value.array;
                 return std::all_of(a.begin(), a.end(), [](const basic_json & el)
                 {
-                    return has_no_children(el.m_data);
+                    return has_no_children(el);
                 });
             }
-            const auto& o = *v.m_value.object;
+            const auto& o = *v.m_data.m_value.object;
             return std::all_of(o.begin(), o.end(), [](const typename object_t::value_type & el)
             {
-                return has_no_children(el.second.m_data);
+                return has_no_children(el.second);
             });
         }
 
@@ -38629,30 +38605,30 @@ private:
 
         // the child of a non-empty array/object v that the walk in
         // destroy_container() continues with (see walk_child_it() above)
-        static data& walk_child(data& v)
+        static basic_json& walk_child(basic_json& v)
         {
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                return v.m_value.array->back().m_data;
+                return v.m_data.m_value.array->back();
             }
-            JSON_ASSERT(v.m_type == value_t::object);
+            JSON_ASSERT(v.m_data.m_type == value_t::object);
-            return walk_child_it(*v.m_value.object)->second.m_data;
+            return walk_child_it(*v.m_data.m_value.object)->second;
         }
 
         // removes walk_child(v) from a non-empty array/object v; this never
         // allocates, and since it is only ever called when that child is a
         // scalar or an already-empty array/object, destroying it never
         // recurses more than one level deep (see destroy() below)
-        static void pop_walk_child(data& v)
+        static void pop_walk_child(basic_json& v)
         {
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                v.m_value.array->pop_back();
+                v.m_data.m_value.array->pop_back();
             }
             else
             {
-                JSON_ASSERT(v.m_type == value_t::object);
+                JSON_ASSERT(v.m_data.m_type == value_t::object);
-                v.m_value.object->erase(walk_child_it(*v.m_value.object));
+                v.m_data.m_value.object->erase(walk_child_it(*v.m_data.m_value.object));
             }
         }
 
@@ -38661,23 +38637,23 @@ private:
         // recurses at most one level deep); this is the same allocator-based
         // free the old recursive implementation used, just factored out so
         // every level of the walk in destroy() can share it
-        static void free_container(data& v) noexcept
+        static void free_container(basic_json& v) noexcept
         {
             JSON_ASSERT(has_no_children(v) || all_children_leaves(v));
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
                 AllocatorType<array_t> alloc;
-                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_value.array);
+                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_data.m_value.array);
-                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_value.array, 1);
+                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_data.m_value.array, 1);
             }
             else
             {
-                JSON_ASSERT(v.m_type == value_t::object);
+                JSON_ASSERT(v.m_data.m_type == value_t::object);
                 AllocatorType<object_t> alloc;
-                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_value.object);
+                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_data.m_value.object);
-                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_value.object, 1);
+                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_data.m_value.object, 1);
             }
-            v.m_type = value_t::null; // avoid a double free if v is later destructed
+            v.m_data.m_type = value_t::null; // avoid a double free if v is later destructed
         }
 
 public:
@@ -38708,16 +38684,14 @@ public:
 
             // This json_value is not itself a basic_json, so the top-level
             // container is first moved into a local stand-in ("cur"); a
-            // default-constructed data has a null pointer in its m_value
+            // default-constructed basic_json has a null pointer in its
-            // (see data::m_value's initializer), so swapping it with *this
+            // m_value (see data::m_value's initializer), so swapping it
-            // leaves this union's own pointer null, and it is never looked
+            // with *this leaves this union's own pointer null, and it is
-            // at or freed a second time. The stand-ins are data, not
+            // never looked at or freed a second time.
-            // basic_json, so that destroying a value never constructs a
+            basic_json cur;
-            // CustomBaseClass, whose constructor may allocate (#5995).
+            cur.m_data.m_type = t;
-            data cur;
-            cur.m_type = t;
             using std::swap;
-            swap(cur.m_value, *this);
+            swap(cur.m_data.m_value, *this);
 
             destroy_bounded(cur, 0);
         }
@@ -38726,7 +38700,7 @@ public:
         // The first recursion_depth_limit() levels are destroyed by plain
         // recursion, which is the fastest way and cannot throw; anything
         // nested deeper is handed to destroy_walk(), which uses no call stack.
-        static void destroy_bounded(data& v, std::size_t depth) noexcept
+        static void destroy_bounded(basic_json& v, std::size_t depth) noexcept
         {
             if (JSON_HEDLEY_UNLIKELY(depth >= detail::recursion_depth_limit()))
             {
@@ -38734,23 +38708,23 @@ public:
                 return;
             }
 
-            if (v.m_type == value_t::array)
+            if (v.m_data.m_type == value_t::array)
             {
-                for (auto& child : *v.m_value.array)
+                for (auto& child : *v.m_data.m_value.array)
                 {
                     if (child.m_data.m_type == value_t::array || child.m_data.m_type == value_t::object)
                     {
-                        destroy_bounded(child.m_data, depth + 1);
+                        destroy_bounded(child, depth + 1);
                     }
                 }
             }
             else
             {
-                for (auto& child : *v.m_value.object)
+                for (auto& child : *v.m_data.m_value.object)
                 {
                     if (child.second.m_data.m_type == value_t::array || child.second.m_data.m_type == value_t::object)
                     {
-                        destroy_bounded(child.second.m_data, depth + 1);
+                        destroy_bounded(child.second, depth + 1);
                     }
                 }
             }
@@ -38777,15 +38751,18 @@ public:
         // array/object, which neither allocates nor recurses more
         // than one level deep.
         //
-        // Like destroy_container(), the walk keeps the containers it
+        // This json_value is not itself a basic_json, so the
-        // holds in data stand-ins (cur, prev, gp, tmp), which never
+        // top-level container is first moved into a local stand-in
-        // construct a CustomBaseClass.
+        // ("cur"); a default-constructed basic_json has a null
-        static void destroy_walk(data& top) noexcept
+        // pointer in its m_value (see data::m_value's initializer),
+        // so swapping it with *this leaves this union's own pointer
+        // null, and it is never looked at or freed a second time.
+        static void destroy_walk(basic_json& top) noexcept
         {
-            data cur;
+            basic_json cur;
             take(cur, top);
 
-            data prev; // value_t::null: no parent
+            basic_json prev; // value_t::null: no parent
 
             // true right after cur was entered: its children have not been
             // looked at yet. If none of them has children of its own, cur is
@@ -38799,7 +38776,7 @@ public:
                 fresh = false;
                 if (has_no_children(cur) || (fresh_now && all_children_leaves(cur)))
                 {
-                    if (prev.m_type == value_t::null)
+                    if (prev.m_data.m_type == value_t::null)
                     {
                         free_container(cur);
                         return; // back at the top with nothing left to do
@@ -38808,7 +38785,7 @@ public:
                     // ascend: detach the grandparent link from prev's
                     // walk_child() slot, drop that (now null) slot, free cur
                     // (it is empty), then move up one level
-                    data gp;
+                    basic_json gp;
                     take(gp, walk_child(prev));
                     pop_walk_child(prev);
 
@@ -38819,7 +38796,7 @@ public:
                     continue;
                 }
 
-                data& cur_child_ref = walk_child(cur);
+                basic_json& cur_child_ref = walk_child(cur);
 
                 if (has_no_children(cur_child_ref))
                 {
@@ -38831,7 +38808,7 @@ public:
                 // descend into the non-empty child, reversing the
                 // link: its slot takes over prev, and the child becomes
                 // the new cur
-                data tmp;
+                basic_json tmp;
                 take(tmp, cur_child_ref);
                 take(cur_child_ref, prev);
                 take(prev, cur);

tests/src/unit-allocator.cpp

@@ -12,6 +12,7 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
+#include <limits>
 #include <valarray>
 #if JSON_HAS_RANGES
     #include <ranges>
@@ -790,7 +791,7 @@ TEST_CASE("a failed allocation leaves the value unchanged")
 #if JSON_HAS_RANGES && !defined(__MINGW32__)
         const std::vector<int> numbers = {1, 2};
         next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, numbers | std::views::filter([](int /*unused*/)
+        CHECK_THROWS_AS(nlohmann::to_json(j, numbers | std::views::filter([](int /*unused*/) noexcept
         {
             return true;
         })), std::bad_alloc&);
@@ -804,3 +805,172 @@ TEST_CASE("a failed allocation leaves the value unchanged")
 #endif
 }
 #endif
+
+#if !defined(JSON_NOEXCEPTION)
+namespace
+{
+// the allocation numbered sweep_fail_at (counted from 1) throws; 0 never fails
+std::size_t sweep_allocations = 0;
+std::size_t sweep_fail_at = 0;
+std::ptrdiff_t sweep_live = 0;
+
+template<class T>
+struct sweep_allocator
+{
+    using value_type = T;
+
+    sweep_allocator() = default;
+    template<class U> sweep_allocator(const sweep_allocator<U>& /*unused*/) noexcept {}
+
+    T* allocate(std::size_t n)
+    {
+        if (sweep_fail_at != 0 && ++sweep_allocations == sweep_fail_at)
+        {
+            throw std::bad_alloc();
+        }
+        ++sweep_live;
+        return std::allocator<T>().allocate(n);
+    }
+
+    void deallocate(T* p, std::size_t n) noexcept
+    {
+        --sweep_live;
+        std::allocator<T>().deallocate(p, n);
+    }
+
+    // GCC 4.8's std::map calls these on the allocator directly instead of
+    // going through std::allocator_traits
+    std::size_t max_size() const noexcept
+    {
+        return (std::numeric_limits<std::size_t>::max)() / sizeof(T);
+    }
+
+    template<class U, class... Args>
+    void construct(U* p, Args&& ... args) noexcept(noexcept(::new (static_cast<void*>(p)) U(std::forward<Args>(args)...)))
+    {
+        ::new (static_cast<void*>(p)) U(std::forward<Args>(args)...);
+    }
+
+    template<class U>
+    void destroy(U* p) noexcept
+    {
+        static_cast<void>(p); // unused for trivially destructible types
+        p->~U();
+    }
+
+    template <class U>
+    struct rebind
+    {
+        using other = sweep_allocator<U>;
+    };
+
+    bool operator==(const sweep_allocator& /*unused*/) const noexcept
+    {
+        return true;
+    }
+    bool operator!=(const sweep_allocator& /*unused*/) const noexcept
+    {
+        return false;
+    }
+};
+
+// run make() with the allocation numbered k failing, for k = 1, 2, ...: every
+// failure must be a std::bad_alloc and must not leave anything behind, and
+// the first k without a failure must yield the value made without failures
+template<class BasicJsonType, class Make>
+void sweep_allocations_of(const Make& make)
+{
+    sweep_fail_at = 0;
+    const BasicJsonType expected = make();
+    const std::ptrdiff_t live_before = sweep_live;
+
+    std::size_t failures = 0;
+    for (std::size_t k = 1; k < 10000; ++k)
+    {
+        sweep_allocations = 0;
+        sweep_fail_at = k;
+        try
+        {
+            const BasicJsonType result = make();
+            sweep_fail_at = 0;
+            CHECK(result == expected);
+            break;
+        }
+        catch (const std::bad_alloc&)
+        {
+            sweep_fail_at = 0;
+            ++failures;
+        }
+        CHECK(sweep_live == live_before);
+    }
+    sweep_fail_at = 0;
+    CHECK(failures > 10);
+    CHECK(sweep_live == live_before);
+}
+} // namespace
+
+TEST_CASE("parse() survives a failing allocation at every point (#5985)")
+{
+    // strings beyond the small string buffer, nested objects and arrays
+    const std::string text = R"({"a":"a long string that does not fit into the small string buffer1","b":[1,2,[3,{"k":"another string that is longer than any small string buffer"}]],"c":{"x":1,"y":{"z":[]},"w":"yet another string that does not fit into a small buffer"},"d":1,"b":[[],{}]})";
+
+    using sweep_json = nlohmann::json::with_allocator_t<sweep_allocator>;
+    using sweep_ordered_json = nlohmann::ordered_json::with_allocator_t<sweep_allocator>;
+
+    SECTION("json")
+    {
+        sweep_allocations_of<sweep_json>([&]
+        {
+            return sweep_json::parse(text);
+        });
+    }
+
+    SECTION("ordered_json")
+    {
+        sweep_allocations_of<sweep_ordered_json>([&]
+        {
+            return sweep_ordered_json::parse(text);
+        });
+    }
+
+    // With iterator debugging (MSVC STL debug builds, also used by clang-cl),
+    // containers allocate a debug proxy through the allocator inside their
+    // noexcept move constructors, so failing that allocation terminates the
+    // program instead of throwing std::bad_alloc. Nothing to check there.
+#if !(defined(_ITERATOR_DEBUG_LEVEL) && _ITERATOR_DEBUG_LEVEL > 0)
+    SECTION("parser callback")
+    {
+        const auto keep_all = [](int /*depth*/, sweep_json::parse_event_t /*event*/, sweep_json& /*parsed*/) noexcept
+        {
+            return true;
+        };
+        sweep_allocations_of<sweep_json>([&]
+        {
+            return sweep_json::parse(text, keep_all);
+        });
+
+        const auto drop_d = [](int /*depth*/, sweep_json::parse_event_t event, sweep_json & parsed)
+        {
+            return event != sweep_json::parse_event_t::key || parsed != "d";
+        };
+        sweep_allocations_of<sweep_json>([&]
+        {
+            return sweep_json::parse(text, drop_d);
+        });
+    }
+#endif
+
+    SECTION("sax_parse into an existing value")
+    {
+        // a failed parse leaves the target in a state that is safe to destroy
+        using sax_t = nlohmann::detail::json_sax_dom_parser<sweep_json, nlohmann::detail::iterator_input_adapter<const char*>>;
+        sweep_allocations_of<sweep_json>([&]() -> sweep_json
+        {
+            sweep_json value;
+            sax_t sax(value, false);
+            static_cast<void>(sweep_json::sax_parse(text, &sax));
+            return value;
+        });
+    }
+}
+#endif

tests/src/unit-bson.cpp

@@ -23,7 +23,6 @@ using nlohmann::json;
 #include <cstdint>
 #include <fstream>
 #include <limits>
-#include <list>
 #include <sstream>
 #include <vector>
 #include "make_test_data_available.hpp"
@@ -1200,31 +1199,6 @@ TEST_CASE("BSON keys from contiguous and stream input")
             from_stream = e.what();
         }
         CHECK(from_vector == from_stream);
-
-        // error_handler_t::strict checks the array element names in place on
-        // contiguous input and byte by byte otherwise; the names are
-        // well-formed, so both give the same value or error as above
-        std::string strict_from_vector;
-        std::string strict_from_list;
-        try
-        {
-            strict_from_vector = json::from_bson(input, true, true, json::error_handler_t::strict).dump();
-        }
-        catch (const json::parse_error& e)
-        {
-            strict_from_vector = e.what();
-        }
-        try
-        {
-            const std::list<std::uint8_t> list(input.begin(), input.end());
-            strict_from_list = json::from_bson(list.begin(), list.end(), true, true, json::error_handler_t::strict).dump();
-        }
-        catch (const json::parse_error& e)
-        {
-            strict_from_list = e.what();
-        }
-        CHECK(strict_from_vector == from_vector);
-        CHECK(strict_from_list == from_vector);
     }
 }
 
@@ -1253,18 +1227,6 @@ TEST_CASE("BSON array element names")
 
     std::istringstream stream(std::string(reinterpret_cast<const char*>(bson.data()), bson.size()));
     CHECK(json::from_bson(stream) == expected);
-
-    // input that is not contiguous reads the names byte by byte and must reject
-    // the same name
-    const std::list<std::uint8_t> list(bson.begin(), bson.end());
-    CHECK_THROWS_WITH_AS(_ = json::from_bson(list.begin(), list.end(), 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&);
-
-    // without exceptions, the rejected name ends the parse
-    CHECK(json::from_bson(bson, true, false, json::error_handler_t::strict).is_discarded());
-
-    // well-formed names pass the check without being stored
-    const json valid = {{"a", {true, false, {{"k", json::array({1, 2})}}}}};
-    CHECK(json::from_bson(json::to_bson(valid), true, true, json::error_handler_t::strict) == valid);
 }
 #endif
 

tests/src/unit-custom-base-class.cpp

@@ -7,7 +7,6 @@
 // SPDX-License-Identifier: MIT
 
 #include <algorithm>
-#include <memory>
 #include <set>
 #include <sstream>
 #include <string>
@@ -496,92 +495,3 @@ TEST_CASE("Regression test for issue #5674 - copy construction must not require
         CHECK(*c == 1);
     }
 }
-
-// counts the constructions and destructions of the base class (#5995)
-struct counting_base
-{
-    static std::size_t constructions;
-    static std::size_t destructions;
-
-    counting_base() noexcept
-    {
-        ++constructions;
-    }
-    counting_base(const counting_base& /*unused*/) noexcept
-    {
-        ++constructions;
-    }
-    counting_base(counting_base&& /*unused*/) noexcept
-    {
-        ++constructions;
-    }
-    counting_base& operator=(const counting_base& /*unused*/) noexcept = default;
-    counting_base& operator=(counting_base&& /*unused*/) noexcept = default;
-    ~counting_base()
-    {
-        ++destructions;
-    }
-
-    static void reset() noexcept
-    {
-        constructions = 0;
-        destructions = 0;
-    }
-};
-
-std::size_t counting_base::constructions = 0;
-std::size_t counting_base::destructions = 0;
-
-using json_with_counting_base = nlohmann::json::with_base_class_t<counting_base>;
-
-TEST_CASE("destroying a value does not construct the custom base class")
-{
-    // regression test for #5995: destroying an array or object used a
-    // default-constructed basic_json as a stand-in, which constructed a base
-    // class that belonged to no value (and could allocate in the noexcept
-    // destructor); now every destroyed value destroys exactly its own base
-    // object, and none is constructed
-    const auto check_destroy = [](std::unique_ptr<json_with_counting_base> j, std::size_t values)
-    {
-        counting_base::reset();
-        j = nullptr;
-        CHECK(counting_base::constructions == 0);
-        CHECK(counting_base::destructions == values);
-    };
-
-    SECTION("scalar")
-    {
-        check_destroy(std::unique_ptr<json_with_counting_base>(new json_with_counting_base(42)), 1);
-    }
-
-    SECTION("array and object")
-    {
-        check_destroy(std::unique_ptr<json_with_counting_base>(new json_with_counting_base(json_with_counting_base::parse(R"({"a":[1,2,3],"b":{"c":true}})"))), 7);
-        check_destroy(std::unique_ptr<json_with_counting_base>(new json_with_counting_base(json_with_counting_base::array())), 1);
-    }
-
-    SECTION("nested deeper than the recursion depth limit")
-    {
-        // alternating arrays and objects, so both kinds of container are
-        // walked by destroy_walk()
-        constexpr std::size_t depth = 1000;
-        std::unique_ptr<json_with_counting_base> j(new json_with_counting_base(json_with_counting_base::array({1, 2})));
-        for (std::size_t i = 0; i < depth; ++i)
-        {
-            json_with_counting_base outer = (i % 2 == 0) ? json_with_counting_base::object() : json_with_counting_base::array();
-            if (outer.is_object())
-            {
-                outer["x"] = std::move(*j);
-                outer["y"] = nullptr;
-            }
-            else
-            {
-                outer.push_back(std::move(*j));
-                outer.push_back(true);
-            }
-            *j = std::move(outer);
-        }
-        // the innermost array with its two elements, and two values per level
-        check_destroy(std::move(j), 3 + (2 * depth));
-    }
-}

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

@@ -521,8 +521,7 @@ 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.insert(0, R"([[1, [2]], )");
+            text = R"([[1, [2]], )" + text + R"(, {"k": [3, {"l": [4]}]}, [5, [6, [7]]]])";
-            text += R"(, {"k": [3, {"l": [4]}]}, [5, [6, [7]]]])";
         }
         CAPTURE(text)
         const json j = json::parse(text);