Install CMake package config files with Meson, and add Meson options

Squashed onto develop from:
- Install CMake package config files with Meson
- meson: Indent code inside an if block
- meson: set a minimum Meson version
- meson: use `override_dependency()` to set dependencies
- meson: use `install_subdir` for headers
- meson: set the C++ standard to C++11
- meson: handle single header and multiheader the same way CMake does
- meson: add support for the GlobalUDLs option
- meson: add support for the ImplictConversions option
- Add meson information to FILES.md
- Complete the Meson options and match CMake's compile definitions
- Add the JSON_* definitions to the CMake pkg-config file
- Document the Meson options and check them in CI
- Fix the Meson CMake target for includedir or datadir outside the prefix
- Avoid //include in Meson-generated CMake target for prefix /
- Add DisableTupleReferenceConversion to Meson and the CMake pkg-config file
- Check in CI that Meson and pkg-config offer the CMake options
- Remove accidentally committed Python bytecode

Co-authored-by: Dylan Baker <dylan@pnwbakers.com>
Signed-off-by: Dylan Baker <dylan@pnwbakers.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/workflows/ubuntu.yml

@@ -31,6 +31,48 @@ jobs:
       - name: Build
         run: cmake --build build --target ci_test_gcc
 
+  ci_meson_install:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+      - name: Check that Meson and pkg-config offer the CMake options
+        run: make check_build_options
+      - name: Install Meson
+        run: pip install meson
+      - name: Install with Meson
+        run: |
+          meson setup build-meson --prefix=${{ github.workspace }}/install
+          meson install -C build-meson
+      - name: Use the installed package with find_package
+        run: |
+          cmake -S tests/cmake_import/project -B build-import -DCMAKE_PREFIX_PATH=${{ github.workspace }}/install
+          cmake --build build-import
+      - name: Install with Meson and non-default options
+        run: |
+          meson setup build-meson-options --prefix=${{ github.workspace }}/install-options -DMultipleHeaders=true -DDiagnostics=true -DGlobalUDLs=false -DDisableTupleReferenceConversion=true
+          meson install -C build-meson-options
+      - name: Check that the options reach the installed files
+        run: |
+          test -d install-options/include/nlohmann/detail
+          cflags=$(PKG_CONFIG_PATH=${{ github.workspace }}/install-options/share/pkgconfig pkg-config --cflags nlohmann_json)
+          echo "$cflags"
+          echo "$cflags" | grep -q -- '-DJSON_DIAGNOSTICS=1'
+          echo "$cflags" | grep -q -- '-DJSON_USE_GLOBAL_UDLS=0'
+          echo "$cflags" | grep -q -- '-DJSON_DISABLE_TUPLE_REFERENCE_CONVERSION=1'
+          grep -q 'JSON_USE_GLOBAL_UDLS=0;JSON_DISABLE_TUPLE_REFERENCE_CONVERSION=1;JSON_DIAGNOSTICS=1' install-options/share/cmake/nlohmann_json/nlohmann_jsonTargets.cmake
+          cmake -S tests/cmake_import/project -B build-import-options -DCMAKE_PREFIX_PATH=${{ github.workspace }}/install-options
+          cmake --build build-import-options
+      - name: Install with Meson and the include directory outside the prefix
+        run: |
+          meson setup build-meson-split --prefix=${{ github.workspace }}/install-split --includedir=${{ github.workspace }}/install-split-dev/include
+          meson install -C build-meson-split
+          cmake -S tests/cmake_import/project -B build-import-split -DCMAKE_PREFIX_PATH=${{ github.workspace }}/install-split
+          cmake --build build-import-split
+
   ci_infer:
     runs-on: ubuntu-latest
     steps:

CMakeLists.txt

@@ -186,7 +186,33 @@ if (MSVC)
     )
 endif()
 
-# Install a pkg-config file, so other tools can find this.
+# Install a pkg-config file, so other tools can find this. It carries the same
+# compile definitions as the target above.
+set(NLOHMANN_JSON_PKGCONFIG_CFLAGS "")
+if (NOT JSON_GlobalUDLs)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_USE_GLOBAL_UDLS=0")
+endif()
+if (NOT JSON_ImplicitConversions)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_USE_IMPLICIT_CONVERSIONS=0")
+endif()
+if (JSON_DisableEnumSerialization)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_DISABLE_ENUM_SERIALIZATION=1")
+endif()
+if (JSON_DisableTupleReferenceConversion)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_DISABLE_TUPLE_REFERENCE_CONVERSION=1")
+endif()
+if (JSON_Diagnostics)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_DIAGNOSTICS=1")
+endif()
+if (JSON_Diagnostic_Positions)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_DIAGNOSTIC_POSITIONS=1")
+endif()
+if (JSON_LegacyDiscardedValueComparison)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1")
+endif()
+if (JSON_StrictNulHandling)
+    string(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -DJSON_STRICT_NUL_HANDLING=1")
+endif()
 configure_file(
     "${CMAKE_CURRENT_SOURCE_DIR}/cmake/pkg-config.pc.in"
     "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"

FILES.md

@@ -249,9 +249,31 @@ make BUILD.bazel
 
 The "Check amalgamation" workflow fails if the file is out of date.
 
-### `meson.build`
+### `meson.build` and `meson_options.txt`
 
-The build definition for the [Meson](https://mesonbuild.com) build system.
+Meson build definitions suitable for use as a subproject ("wrap" in Meson terminology).
+
+Projects wishing to use the wrap can execute:
+```sh
+meson wrap install nlohmann_json
+```
+
+Which allows Meson to build from source when a system provided dependency isn't available.
+
+To build directly:
+```sh
+meson setup builddir
+ninja -C builddir
+```
+
+`meson_options.txt` defines the options, which mirror the CMake options that change the library's target (for example,
+`-DDiagnostics=true`). Meson requires this file next to `meson.build`, so it is also part of `include.zip`. `make check_build_options`
+([`tools/check_build_options`](tools/check_build_options/README.md)) checks in CI that both files and the pkg-config files
+stay in sync with the CMake options.
+
+When installing, `meson.build` installs the headers, a pkg-config file, and the CMake package config files, so that
+`find_package(nlohmann_json)` works. As Meson cannot generate `nlohmann_jsonTargets.cmake` itself, it is created from
+the template `cmake/nlohmann_jsonTargets.cmake.in`, which is only used by Meson.
 
 ### `Package.swift`
 

Makefile

@@ -1,4 +1,4 @@
-.PHONY: pretty clean ChangeLog.md release update_hedley update_hedley_undef BUILD.bazel natvis macro_builder_check
+.PHONY: pretty clean ChangeLog.md release update_hedley update_hedley_undef BUILD.bazel natvis macro_builder_check check_build_options
 
 ##########################################################################
 # configuration
@@ -124,6 +124,10 @@ macro_builder_check:
 	diff "$$TMPDIR/paste.hpp" "$$TMPDIR/paste_actual.hpp" || (echo "===================================================================\n  $(MACRO_SCOPE_HPP) (NLOHMANN_JSON_EXPAND..NLOHMANN_JSON_DOUBLE_PASTE63) is out of date!\n  Regenerate it, see tools/macro_builder/README.md.\n===================================================================" ; exit 1); \
 	diff "$$TMPDIR/type_body.hpp" "$$TMPDIR/type_body_actual.hpp" || (echo "===================================================================\n  $(MACRO_SCOPE_HPP) (NLOHMANN_JSON_TYPE_BODY) is out of date!\n  Regenerate it, see tools/macro_builder/README.md.\n===================================================================" ; exit 1)
 
+# check that the Meson build and the pkg-config files offer the options of the CMake target
+check_build_options:
+	python3 tools/check_build_options/check_build_options.py .
+
 # check if file single_include/nlohmann/json.hpp has been amalgamated from the nlohmann sources
 check-amalgamation:
 	@mv $(AMALGAMATED_FILE) $(AMALGAMATED_FILE)~
@@ -181,7 +185,7 @@ json.tar.xz:
 # We use `-X` to make the resulting ZIP file reproducible, see
 # <https://content.pivotal.io/blog/barriers-to-deterministic-reproducible-zip-files>.
 include.zip: BUILD.bazel
-	zip -9 --recurse-paths -X include.zip $(SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) $(AMALGAMATED_LITERALS_FILE) BUILD.bazel MODULE.bazel meson.build LICENSE.MIT
+	zip -9 --recurse-paths -X include.zip $(SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) $(AMALGAMATED_LITERALS_FILE) BUILD.bazel MODULE.bazel meson.build meson_options.txt LICENSE.MIT
 
 # Create the files for a release and add signatures and hashes.
 release: include.zip json.tar.xz

cmake/nlohmann_jsonTargets.cmake.in

@@ -0,0 +1,42 @@
+# Imported target for installations made with Meson (see meson.build).
+#
+# CMake installations generate this file with install(EXPORT ...). Meson cannot
+# do that, but as the library is header-only, the target only needs an include
+# directory, the C++ standard, and the compile definitions of the options that
+# differ from their defaults. Paths are computed relative to this file so that
+# the installation can be relocated (e.g., into a sysroot), unless includedir or
+# datadir is outside the prefix.
+
+if(TARGET @PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@)
+    return()
+endif()
+
+get_filename_component(_IMPORT_PREFIX "${CMAKE_CURRENT_LIST_DIR}/@NLOHMANN_JSON_CONFIG_TO_PREFIX@" ABSOLUTE)
+# As in CMake's generated file: avoid "//include" for an installation to "/".
+if(_IMPORT_PREFIX STREQUAL "/")
+    set(_IMPORT_PREFIX "")
+endif()
+
+add_library(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ INTERFACE IMPORTED)
+set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+    INTERFACE_INCLUDE_DIRECTORIES "@NLOHMANN_JSON_INCLUDE_DIR@"
+)
+if(CMAKE_VERSION VERSION_LESS 3.8)
+    set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+        INTERFACE_COMPILE_FEATURES cxx_range_for
+    )
+else()
+    set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+        INTERFACE_COMPILE_FEATURES cxx_std_11
+    )
+endif()
+
+set(_NLOHMANN_JSON_COMPILE_DEFINITIONS "@NLOHMANN_JSON_COMPILE_DEFINITIONS@")
+if(_NLOHMANN_JSON_COMPILE_DEFINITIONS)
+    set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+        INTERFACE_COMPILE_DEFINITIONS "${_NLOHMANN_JSON_COMPILE_DEFINITIONS}"
+    )
+endif()
+
+unset(_NLOHMANN_JSON_COMPILE_DEFINITIONS)
+unset(_IMPORT_PREFIX)

cmake/pkg-config.pc.in

@@ -4,4 +4,4 @@ includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
 Name: @PROJECT_NAME@
 Description: JSON for Modern C++
 Version: @PROJECT_VERSION@
-Cflags: -I${includedir}
+Cflags: -I${includedir}@NLOHMANN_JSON_PKGCONFIG_CFLAGS@

docs/mkdocs/docs/integration/package_managers.md

@@ -125,10 +125,23 @@ meson wrap install nlohmann_json
 Please see the Meson project for any issues regarding the packaging.
 
 The provided `meson.build` can also be used as an alternative to CMake for installing `nlohmann_json` system-wide in
-which case a [pkg-config](pkg-config.md) file is installed. To use it, have your build system require the
+which case a [pkg-config](pkg-config.md) file and the CMake package config files are installed. To use it, have your build system require
-`nlohmann_json` pkg-config dependency. In Meson, it is preferred to use the
+the `nlohmann_json` pkg-config dependency, or use [`find_package(nlohmann_json)`](cmake.md#external) in CMake. In Meson,
-[`dependency()`](https://mesonbuild.com/Reference-manual.html#dependency) object with a subproject fallback, rather than
+it is preferred to use the [`dependency()`](https://mesonbuild.com/Reference-manual.html#dependency) object with a
-using the subproject directly.
+subproject fallback, rather than using the subproject directly.
+
+The options that change the library's configuration are available in Meson as well, named like the
+[CMake options](cmake.md#cmake-options) without the `JSON_` prefix: `MultipleHeaders`, `GlobalUDLs`,
+`ImplicitConversions`, `DisableEnumSerialization`, `DisableTupleReferenceConversion`, `Diagnostics`,
+`Diagnostic_Positions`, `LegacyDiscardedValueComparison`, and `StrictNulHandling`. They have the same defaults as in CMake, except that
+`MultipleHeaders` is `false`. Set them with `-D` when setting up the build, or with the subproject name as prefix when
+the library is used as a subproject:
+
+```shell
+meson setup build -Dnlohmann_json:Diagnostics=true
+```
+
+The resulting compile definitions are part of the Meson dependency, the pkg-config file, and the CMake target.
 
 ??? example "Example: Wrap"
 

include/nlohmann/detail/conversions/to_json.hpp

@@ -43,10 +43,6 @@ namespace detail
  * j.m_data.m_value.destroy(j.m_data.m_type) to avoid a memory leak in case j contains an
  * allocated value (e.g., a string). See bug issue
  * https://github.com/nlohmann/json/issues/2865 for more information.
- *
- * A value that has to be allocated is created before the old one is destroyed:
- * were it the other way around, an exception while creating the new value would
- * leave j with the type of the new value, but the pointer to the destroyed old one.
  */
 
 template<value_t> struct external_constructor;
@@ -70,20 +66,18 @@ struct external_constructor<value_t::string>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::string_t& s)
     {
-        const typename BasicJsonType::json_value value(s);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value = value;
+        j.m_data.m_value = s;
         j.assert_invariant();
     }
 
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::string_t&& s)
     {
-        const typename BasicJsonType::json_value value(std::move(s));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value = value;
+        j.m_data.m_value = std::move(s);
         j.assert_invariant();
     }
 
@@ -92,10 +86,9 @@ struct external_constructor<value_t::string>
                              int > = 0 >
     static void construct(BasicJsonType& j, const CompatibleStringType& str)
     {
-        auto* created = j.template create<typename BasicJsonType::string_t>(str);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value.string = created;
+        j.m_data.m_value.string = j.template create<typename BasicJsonType::string_t>(str);
         j.assert_invariant();
     }
 };
@@ -106,20 +99,18 @@ struct external_constructor<value_t::binary>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::binary_t& b)
     {
-        const typename BasicJsonType::json_value value(b);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::binary;
-        j.m_data.m_value = value;
+        j.m_data.m_value = typename BasicJsonType::binary_t(b);
         j.assert_invariant();
     }
 
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::binary_t&& b)
     {
-        const typename BasicJsonType::json_value value(std::move(b));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::binary;
-        j.m_data.m_value = value;
+        j.m_data.m_value = typename BasicJsonType::binary_t(std::move(b));
         j.assert_invariant();
     }
 };
@@ -169,10 +160,9 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::array_t& arr)
     {
-        const typename BasicJsonType::json_value value(arr);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = arr;
         j.set_parents();
         j.assert_invariant();
     }
@@ -180,10 +170,9 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::array_t&& arr)
     {
-        const typename BasicJsonType::json_value value(std::move(arr));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = std::move(arr);
         j.set_parents();
         j.assert_invariant();
     }
@@ -199,10 +188,9 @@ struct external_constructor<value_t::array>
         using std::begin;
         using std::end;
 
-        auto* created = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value.array = created;
+        j.m_data.m_value.array = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
         j.set_parents();
         j.assert_invariant();
     }
@@ -210,17 +198,15 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const std::vector<bool>& arr)
     {
-        typename BasicJsonType::array_t elements;
-        elements.reserve(arr.size());
-        for (const bool x : arr)
-        {
-            elements.push_back(x);
-        }
-        const typename BasicJsonType::json_value value(std::move(elements));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = value_t::array;
-        j.set_parents();
+        j.m_data.m_value.array->reserve(arr.size());
+        for (const bool x : arr)
+        {
+            j.m_data.m_value.array->push_back(x);
+            j.set_parent(j.m_data.m_value.array->back());
+        }
         j.assert_invariant();
     }
 
@@ -228,12 +214,11 @@ struct external_constructor<value_t::array>
              enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
     static void construct(BasicJsonType& j, const std::valarray<T>& arr)
     {
-        typename BasicJsonType::array_t elements(arr.size());
-        std::copy(std::begin(arr), std::end(arr), elements.begin());
-        const typename BasicJsonType::json_value value(std::move(elements));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = value_t::array;
+        j.m_data.m_value.array->resize(arr.size());
+        std::copy(std::begin(arr), std::end(arr), j.m_data.m_value.array->begin());
         j.set_parents();
         j.assert_invariant();
     }
@@ -243,15 +228,13 @@ struct external_constructor<value_t::array>
              enable_if_t<is_compatible_range_view<std::remove_cvref_t<CompatibleArrayType>>::value, int> = 0>
     static void construct(BasicJsonType& j, CompatibleArrayType && arr)
     {
-        typename BasicJsonType::array_t elements;
-        for (auto&& x : std::forward<CompatibleArrayType>(arr))
-        {
-            elements.push_back(x);
-        }
-        const typename BasicJsonType::json_value value(std::move(elements));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = value_t::array;
+        for (auto&& x : std::forward<CompatibleArrayType>(arr))
+        {
+            j.m_data.m_value.array->push_back(x);
+        }
         // set the parents only once all elements are in place: a push_back
         // that reallocates moves the earlier elements, which does not keep
         // their parent pointers
@@ -267,10 +250,9 @@ struct external_constructor<value_t::object>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::object_t& obj)
     {
-        const typename BasicJsonType::json_value value(obj);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value = value;
+        j.m_data.m_value = obj;
         j.set_parents();
         j.assert_invariant();
     }
@@ -278,10 +260,9 @@ struct external_constructor<value_t::object>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
     {
-        const typename BasicJsonType::json_value value(std::move(obj));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value = value;
+        j.m_data.m_value = std::move(obj);
         j.set_parents();
         j.assert_invariant();
     }
@@ -293,10 +274,9 @@ struct external_constructor<value_t::object>
         using std::begin;
         using std::end;
 
-        auto* created = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value.object = created;
+        j.m_data.m_value.object = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
         j.set_parents();
         j.assert_invariant();
     }

include/nlohmann/json.hpp

@@ -2056,8 +2056,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         if (is_an_object)
         {
             // the initializer list is a list of pairs -> create an object
-            m_data.m_value = value_t::object;
             m_data.m_type = value_t::object;
+            m_data.m_value = value_t::object;
 
             for (auto& element_ref : init)
             {
@@ -2079,8 +2079,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             }
 #endif
             // the initializer list describes an array -> create an array
-            m_data.m_value.array = create<array_t>(init.begin(), init.end());
             m_data.m_type = value_t::array;
+            m_data.m_value.array = create<array_t>(init.begin(), init.end());
         }
 
         set_parents();
@@ -2093,8 +2093,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(const typename binary_t::container_type& init)
     {
         auto res = basic_json();
-        res.m_data.m_value = init;
         res.m_data.m_type = value_t::binary;
+        res.m_data.m_value = init;
         return res;
     }
 
@@ -2104,8 +2104,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(const typename binary_t::container_type& init, typename binary_t::subtype_type subtype)
     {
         auto res = basic_json();
-        res.m_data.m_value = binary_t(init, subtype);
         res.m_data.m_type = value_t::binary;
+        res.m_data.m_value = binary_t(init, subtype);
         return res;
     }
 
@@ -2115,8 +2115,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(typename binary_t::container_type&& init)
     {
         auto res = basic_json();
-        res.m_data.m_value = std::move(init);
         res.m_data.m_type = value_t::binary;
+        res.m_data.m_value = std::move(init);
         return res;
     }
 
@@ -2126,8 +2126,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(typename binary_t::container_type&& init, typename binary_t::subtype_type subtype)
     {
         auto res = basic_json();
-        res.m_data.m_value = binary_t(std::move(init), subtype);
         res.m_data.m_type = value_t::binary;
+        res.m_data.m_value = binary_t(std::move(init), subtype);
         return res;
     }
 

meson.build

@@ -2,24 +2,114 @@ project('nlohmann_json',
     'cpp',
     version : '3.12.0',
     license : 'MIT',
+    meson_version : '>= 0.64',
+    default_options: ['cpp_std=c++11'],
 )
 
+if get_option('MultipleHeaders')
+    incdir = 'include'
+else
+    incdir = 'single_include'
+endif
+
+# The same compile definitions as the CMake target (see target_compile_definitions
+# in CMakeLists.txt): only an option that differs from its default adds one.
+json_defines = []
+if not get_option('GlobalUDLs')
+    json_defines += 'JSON_USE_GLOBAL_UDLS=0'
+endif
+if not get_option('ImplicitConversions')
+    json_defines += 'JSON_USE_IMPLICIT_CONVERSIONS=0'
+endif
+if get_option('DisableEnumSerialization')
+    json_defines += 'JSON_DISABLE_ENUM_SERIALIZATION=1'
+endif
+if get_option('DisableTupleReferenceConversion')
+    json_defines += 'JSON_DISABLE_TUPLE_REFERENCE_CONVERSION=1'
+endif
+if get_option('Diagnostics')
+    json_defines += 'JSON_DIAGNOSTICS=1'
+endif
+if get_option('Diagnostic_Positions')
+    json_defines += 'JSON_DIAGNOSTIC_POSITIONS=1'
+endif
+if get_option('LegacyDiscardedValueComparison')
+    json_defines += 'JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1'
+endif
+if get_option('StrictNulHandling')
+    json_defines += 'JSON_STRICT_NUL_HANDLING=1'
+endif
+
+cpp_args = []
+foreach define : json_defines
+    cpp_args += '-D' + define
+endforeach
+
 nlohmann_json_dep = declare_dependency(
-    include_directories: include_directories('single_include')
+    compile_args: cpp_args,
+    include_directories: include_directories(incdir)
 )
+meson.override_dependency('nlohmann_json', nlohmann_json_dep)
 
+# The multi-header version under the name earlier versions of this file used
 nlohmann_json_multiple_headers = declare_dependency(
+    compile_args: cpp_args,
     include_directories: include_directories('include')
 )
 
 if not meson.is_subproject()
-install_headers('single_include/nlohmann/json.hpp', subdir: 'nlohmann')
+    install_subdir(
-install_headers('single_include/nlohmann/json_fwd.hpp', subdir: 'nlohmann')
+        incdir / 'nlohmann',
-install_headers('single_include/nlohmann/json_literals.hpp', subdir: 'nlohmann')
+        install_dir: get_option('includedir'),
+        install_tag: 'devel',
+    )
 
-pkgc = import('pkgconfig')
+    pkgc = import('pkgconfig')
-pkgc.generate(name: 'nlohmann_json',
+    pkgc.generate(name: 'nlohmann_json',
-    version: meson.project_version(),
+        version: meson.project_version(),
-    description: 'JSON for Modern C++'
+        description: 'JSON for Modern C++',
-)
+        extra_cflags: cpp_args,
+        install_dir: get_option('datadir') / 'pkgconfig',
+    )
+
+    # CMake package config files, so that find_package(nlohmann_json) works. The
+    # include directory is given relative to the config files, so that the
+    # installation can be relocated. This is not possible if includedir or datadir
+    # is an absolute path outside the prefix (e.g., with the separate outputs of
+    # Nix); then the absolute include directory is used, as CMake does.
+    fs = import('fs')
+    cmake_install_dir = get_option('datadir') / 'cmake' / meson.project_name()
+    cmake_to_prefix = []
+    if fs.is_absolute(get_option('includedir')) or fs.is_absolute(cmake_install_dir)
+        cmake_include_dir = (get_option('prefix') / get_option('includedir')).replace('\\', '/')
+    else
+        foreach component : cmake_install_dir.split('/')
+            cmake_to_prefix += '..'
+        endforeach
+        cmake_include_dir = '${_IMPORT_PREFIX}/' + get_option('includedir')
+    endif
+
+    cmake_conf = configuration_data()
+    cmake_conf.set('PROJECT_NAME', meson.project_name())
+    cmake_conf.set('PROJECT_VERSION', meson.project_version())
+    cmake_conf.set('PROJECT_VERSION_MAJOR', meson.project_version().split('.')[0])
+    cmake_conf.set('NLOHMANN_JSON_TARGET_NAME', meson.project_name())
+    cmake_conf.set('NLOHMANN_JSON_TARGETS_EXPORT_NAME', meson.project_name() + 'Targets')
+    cmake_conf.set('NLOHMANN_JSON_INCLUDE_DIR', cmake_include_dir)
+    cmake_conf.set('NLOHMANN_JSON_CONFIG_TO_PREFIX', '/'.join(cmake_to_prefix))
+    cmake_conf.set('NLOHMANN_JSON_COMPILE_DEFINITIONS', ';'.join(json_defines))
+
+    foreach cmake_file : [
+        ['cmake/config.cmake.in', 'nlohmann_jsonConfig.cmake'],
+        ['cmake/nlohmann_jsonConfigVersion.cmake.in', 'nlohmann_jsonConfigVersion.cmake'],
+        ['cmake/nlohmann_jsonTargets.cmake.in', 'nlohmann_jsonTargets.cmake'],
+    ]
+        configure_file(
+            input: cmake_file[0],
+            output: cmake_file[1],
+            configuration: cmake_conf,
+            format: 'cmake@',
+            install_dir: cmake_install_dir,
+        )
+    endforeach
 endif

meson_options.txt

@@ -0,0 +1,54 @@
+option(
+    'MultipleHeaders',
+    type: 'boolean',
+    value: false,
+    description: 'Use non-amalgamated version of the library',
+)
+option(
+    'GlobalUDLs',
+    type: 'boolean',
+    value: true,
+    description: 'Place user-defined string literals in the global namespace',
+)
+option(
+    'ImplicitConversions',
+    type: 'boolean',
+    value: true,
+    description: 'Enable implicit conversions',
+)
+option(
+    'DisableEnumSerialization',
+    type: 'boolean',
+    value: false,
+    description: 'Disable default integer enum serialization',
+)
+option(
+    'DisableTupleReferenceConversion',
+    type: 'boolean',
+    value: false,
+    description: 'Disable conversion from a one-element tuple of a JSON reference',
+)
+option(
+    'Diagnostics',
+    type: 'boolean',
+    value: false,
+    description: 'Use extended diagnostic messages',
+)
+option(
+    'Diagnostic_Positions',
+    type: 'boolean',
+    value: false,
+    description: 'Enable diagnostic positions',
+)
+option(
+    'LegacyDiscardedValueComparison',
+    type: 'boolean',
+    value: false,
+    description: 'Enable legacy discarded value comparison',
+)
+option(
+    'StrictNulHandling',
+    type: 'boolean',
+    value: false,
+    description: 'Enable strict NUL-byte handling',
+)

single_include/nlohmann/json.hpp

@@ -6837,10 +6837,6 @@ namespace detail
  * j.m_data.m_value.destroy(j.m_data.m_type) to avoid a memory leak in case j contains an
  * allocated value (e.g., a string). See bug issue
  * https://github.com/nlohmann/json/issues/2865 for more information.
- *
- * A value that has to be allocated is created before the old one is destroyed:
- * were it the other way around, an exception while creating the new value would
- * leave j with the type of the new value, but the pointer to the destroyed old one.
  */
 
 template<value_t> struct external_constructor;
@@ -6864,20 +6860,18 @@ struct external_constructor<value_t::string>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::string_t& s)
     {
-        const typename BasicJsonType::json_value value(s);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value = value;
+        j.m_data.m_value = s;
         j.assert_invariant();
     }
 
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::string_t&& s)
     {
-        const typename BasicJsonType::json_value value(std::move(s));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value = value;
+        j.m_data.m_value = std::move(s);
         j.assert_invariant();
     }
 
@@ -6886,10 +6880,9 @@ struct external_constructor<value_t::string>
                              int > = 0 >
     static void construct(BasicJsonType& j, const CompatibleStringType& str)
     {
-        auto* created = j.template create<typename BasicJsonType::string_t>(str);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value.string = created;
+        j.m_data.m_value.string = j.template create<typename BasicJsonType::string_t>(str);
         j.assert_invariant();
     }
 };
@@ -6900,20 +6893,18 @@ struct external_constructor<value_t::binary>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::binary_t& b)
     {
-        const typename BasicJsonType::json_value value(b);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::binary;
-        j.m_data.m_value = value;
+        j.m_data.m_value = typename BasicJsonType::binary_t(b);
         j.assert_invariant();
     }
 
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::binary_t&& b)
     {
-        const typename BasicJsonType::json_value value(std::move(b));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::binary;
-        j.m_data.m_value = value;
+        j.m_data.m_value = typename BasicJsonType::binary_t(std::move(b));
         j.assert_invariant();
     }
 };
@@ -6963,10 +6954,9 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::array_t& arr)
     {
-        const typename BasicJsonType::json_value value(arr);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = arr;
         j.set_parents();
         j.assert_invariant();
     }
@@ -6974,10 +6964,9 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::array_t&& arr)
     {
-        const typename BasicJsonType::json_value value(std::move(arr));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = std::move(arr);
         j.set_parents();
         j.assert_invariant();
     }
@@ -6993,10 +6982,9 @@ struct external_constructor<value_t::array>
         using std::begin;
         using std::end;
 
-        auto* created = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value.array = created;
+        j.m_data.m_value.array = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
         j.set_parents();
         j.assert_invariant();
     }
@@ -7004,17 +6992,15 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const std::vector<bool>& arr)
     {
-        typename BasicJsonType::array_t elements;
-        elements.reserve(arr.size());
-        for (const bool x : arr)
-        {
-            elements.push_back(x);
-        }
-        const typename BasicJsonType::json_value value(std::move(elements));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = value_t::array;
-        j.set_parents();
+        j.m_data.m_value.array->reserve(arr.size());
+        for (const bool x : arr)
+        {
+            j.m_data.m_value.array->push_back(x);
+            j.set_parent(j.m_data.m_value.array->back());
+        }
         j.assert_invariant();
     }
 
@@ -7022,12 +7008,11 @@ struct external_constructor<value_t::array>
              enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
     static void construct(BasicJsonType& j, const std::valarray<T>& arr)
     {
-        typename BasicJsonType::array_t elements(arr.size());
-        std::copy(std::begin(arr), std::end(arr), elements.begin());
-        const typename BasicJsonType::json_value value(std::move(elements));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = value_t::array;
+        j.m_data.m_value.array->resize(arr.size());
+        std::copy(std::begin(arr), std::end(arr), j.m_data.m_value.array->begin());
         j.set_parents();
         j.assert_invariant();
     }
@@ -7037,15 +7022,13 @@ struct external_constructor<value_t::array>
              enable_if_t<is_compatible_range_view<std::remove_cvref_t<CompatibleArrayType>>::value, int> = 0>
     static void construct(BasicJsonType& j, CompatibleArrayType && arr)
     {
-        typename BasicJsonType::array_t elements;
-        for (auto&& x : std::forward<CompatibleArrayType>(arr))
-        {
-            elements.push_back(x);
-        }
-        const typename BasicJsonType::json_value value(std::move(elements));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value;
+        j.m_data.m_value = value_t::array;
+        for (auto&& x : std::forward<CompatibleArrayType>(arr))
+        {
+            j.m_data.m_value.array->push_back(x);
+        }
         // set the parents only once all elements are in place: a push_back
         // that reallocates moves the earlier elements, which does not keep
         // their parent pointers
@@ -7061,10 +7044,9 @@ struct external_constructor<value_t::object>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::object_t& obj)
     {
-        const typename BasicJsonType::json_value value(obj);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value = value;
+        j.m_data.m_value = obj;
         j.set_parents();
         j.assert_invariant();
     }
@@ -7072,10 +7054,9 @@ struct external_constructor<value_t::object>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
     {
-        const typename BasicJsonType::json_value value(std::move(obj));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value = value;
+        j.m_data.m_value = std::move(obj);
         j.set_parents();
         j.assert_invariant();
     }
@@ -7087,10 +7068,9 @@ struct external_constructor<value_t::object>
         using std::begin;
         using std::end;
 
-        auto* created = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value.object = created;
+        j.m_data.m_value.object = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
         j.set_parents();
         j.assert_invariant();
     }
@@ -29256,8 +29236,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         if (is_an_object)
         {
             // the initializer list is a list of pairs -> create an object
-            m_data.m_value = value_t::object;
             m_data.m_type = value_t::object;
+            m_data.m_value = value_t::object;
 
             for (auto& element_ref : init)
             {
@@ -29279,8 +29259,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             }
 #endif
             // the initializer list describes an array -> create an array
-            m_data.m_value.array = create<array_t>(init.begin(), init.end());
             m_data.m_type = value_t::array;
+            m_data.m_value.array = create<array_t>(init.begin(), init.end());
         }
 
         set_parents();
@@ -29293,8 +29273,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(const typename binary_t::container_type& init)
     {
         auto res = basic_json();
-        res.m_data.m_value = init;
         res.m_data.m_type = value_t::binary;
+        res.m_data.m_value = init;
         return res;
     }
 
@@ -29304,8 +29284,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(const typename binary_t::container_type& init, typename binary_t::subtype_type subtype)
     {
         auto res = basic_json();
-        res.m_data.m_value = binary_t(init, subtype);
         res.m_data.m_type = value_t::binary;
+        res.m_data.m_value = binary_t(init, subtype);
         return res;
     }
 
@@ -29315,8 +29295,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(typename binary_t::container_type&& init)
     {
         auto res = basic_json();
-        res.m_data.m_value = std::move(init);
         res.m_data.m_type = value_t::binary;
+        res.m_data.m_value = std::move(init);
         return res;
     }
 
@@ -29326,8 +29306,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(typename binary_t::container_type&& init, typename binary_t::subtype_type subtype)
     {
         auto res = basic_json();
-        res.m_data.m_value = binary_t(std::move(init), subtype);
         res.m_data.m_type = value_t::binary;
+        res.m_data.m_value = binary_t(std::move(init), subtype);
         return res;
     }
 

tests/CMakeLists.txt

@@ -141,11 +141,6 @@ json_test_set_test_options(test-unicode4 TEST_PROPERTIES TIMEOUT 3000)
 # only the #972 regression test needs thirdparty/fifo_map on its include path
 json_test_set_test_options(test-regression1 LINK_LIBRARIES fifo_map_include)
 
-# GCC's false -Warray-bounds error with JSON_DIAGNOSTICS only shows up when optimizing (#5742)
-json_test_set_test_options(test-diagnostics-optimized
-    COMPILE_OPTIONS $<$<CXX_COMPILER_ID:GNU>:-O3 -Werror=array-bounds>
-)
-
 #############################################################################
 # add unit tests
 #############################################################################

tests/src/unit-allocator.cpp

@@ -12,11 +12,6 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
-#include <valarray>
-#if JSON_HAS_RANGES
-    #include <ranges>
-#endif
-
 namespace
 {
 // special test case to check if memory is leaked if constructor throws
@@ -612,173 +607,3 @@ TEST_CASE("bad my_allocator::construct")
         j["test"].push_back("should not leak");
     }
 }
-
-// the no-exceptions CI job skips every CHECK_THROWS_AS, which would leave
-// next_construct_fails set for the next allocation outside a check
-#if !defined(JSON_NOEXCEPTION)
-TEST_CASE("a failed allocation leaves the value unchanged")
-{
-    // create JSON type using the throwing allocator
-    using my_json = nlohmann::basic_json<std::map,
-          std::vector,
-          std::string,
-          bool,
-          std::int64_t,
-          std::uint64_t,
-          double,
-          my_allocator>;
-
-    // Each of these creates a string, array, object, or binary value. The
-    // value must be created before the type is changed: otherwise, a failed
-    // creation left a value of the new type without anything behind it (an
-    // assertion in its destructor, a null pointer everywhere else) or, when
-    // an old value was destroyed first, with a pointer to that destroyed one.
-
-    SECTION("creating a binary value")
-    {
-        const std::vector<std::uint8_t> bytes = {1, 2, 3};
-        my_json _;
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(_ = my_json::binary(bytes), std::bad_alloc&);
-        next_construct_fails = true;
-        CHECK_THROWS_AS(_ = my_json::binary(bytes, 42), std::bad_alloc&);
-        next_construct_fails = true;
-        CHECK_THROWS_AS(_ = my_json::binary(std::vector<std::uint8_t>(bytes)), std::bad_alloc&);
-        next_construct_fails = true;
-        CHECK_THROWS_AS(_ = my_json::binary(std::vector<std::uint8_t>(bytes), 42), std::bad_alloc&);
-        next_construct_fails = false;
-    }
-
-    SECTION("turning a null value into an array or object")
-    {
-        my_json j;
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(j[0], std::bad_alloc&);
-        CHECK(j.is_null());
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(j["key"], std::bad_alloc&);
-        CHECK(j.is_null());
-
-#ifdef JSON_HAS_CPP_17
-        next_construct_fails = true;
-        CHECK_THROWS_AS(j[std::string_view("key")], std::bad_alloc&);
-        CHECK(j.is_null());
-#endif
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(j.push_back(my_json(1)), std::bad_alloc&);
-        CHECK(j.is_null());
-
-        const my_json one = 1;
-        next_construct_fails = true;
-        CHECK_THROWS_AS(j.push_back(one), std::bad_alloc&);
-        CHECK(j.is_null());
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(j.push_back(my_json::object_t::value_type("key", 1)), std::bad_alloc&);
-        CHECK(j.is_null());
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(j.emplace_back(1), std::bad_alloc&);
-        CHECK(j.is_null());
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(j.emplace("key", 1), std::bad_alloc&);
-        CHECK(j.is_null());
-
-        const my_json object = {{"key", 1}};
-        next_construct_fails = true;
-        CHECK_THROWS_AS(j.update(object), std::bad_alloc&);
-        CHECK(j.is_null());
-
-        next_construct_fails = false;
-    }
-
-    // With iterator debugging, VS 2015's containers construct a proxy with the
-    // allocator in constructors that cannot report its failure, so a failing
-    // allocator crashes this section there (SIGSEGV with VS 2015 Debug x86).
-#if !(defined(_MSC_VER) && _MSC_VER < 1910 && defined(_ITERATOR_DEBUG_LEVEL) && _ITERATOR_DEBUG_LEVEL > 0)
-    SECTION("converting into an existing value")
-    {
-        // to_json replaces the value it is given; the old one must survive a
-        // failed creation of the new one
-        my_json j = "old";
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, std::string("new")), std::bad_alloc&);
-        CHECK(j == "old");
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, std::vector<int> {1, 2}), std::bad_alloc&);
-        CHECK(j == "old");
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, std::vector<bool> {true, false}), std::bad_alloc&);
-        CHECK(j == "old");
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, std::map<std::string, int> {{"a", 1}}), std::bad_alloc&);
-        CHECK(j == "old");
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, my_json::binary_t({1, 2})), std::bad_alloc&);
-        CHECK(j == "old");
-
-        // the overloads for lvalues of the value types, for the value types
-        // themselves, and for the remaining compatible types
-        const std::string string = "new";
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, string), std::bad_alloc&);
-        CHECK(j == "old");
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, "new"), std::bad_alloc&);
-        CHECK(j == "old");
-
-        // to_json only moves a binary value that it converted from another
-        // container type, which my_json's std::vector<std::uint8_t> is not
-        using binary_constructor = nlohmann::detail::external_constructor<nlohmann::detail::value_t::binary>;
-        next_construct_fails = true;
-        CHECK_THROWS_AS(binary_constructor::construct(j, my_json::binary_t({1, 2})), std::bad_alloc&);
-        CHECK(j == "old");
-
-        my_json::array_t array = {1, 2};
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, array), std::bad_alloc&);
-        CHECK(j == "old");
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, std::move(array)), std::bad_alloc&);
-        CHECK(j == "old");
-
-        my_json::object_t object = {{"a", 1}};
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, object), std::bad_alloc&);
-        CHECK(j == "old");
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, std::move(object)), std::bad_alloc&);
-        CHECK(j == "old");
-
-        next_construct_fails = true;
-        CHECK_THROWS_AS(nlohmann::to_json(j, std::valarray<int> {1, 2}), std::bad_alloc&);
-        CHECK(j == "old");
-
-#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*/)
-        {
-            return true;
-        })), std::bad_alloc&);
-        CHECK(j == "old");
-#endif
-
-        next_construct_fails = false;
-        nlohmann::to_json(j, std::vector<int> {1, 2});
-        CHECK(j == my_json({1, 2}));
-    }
-#endif
-}
-#endif

tests/src/unit-diagnostics-optimized.cpp

@@ -1,80 +0,0 @@
-//     __ _____ _____ _____
-//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
-// |  |  |__   |  |  | | | |  version 3.12.0
-// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
-//
-// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
-// SPDX-License-Identifier: MIT
-
-// Regression test for https://github.com/nlohmann/json/issues/5742: with
-// JSON_DIAGNOSTICS, GCC (12 to at least 16) reported a false -Warray-bounds
-// error in the inlined set_parents() at -O3. The type of a new string was set
-// before the string was allocated, so GCC had to assume that operator new
-// could change it again and checked the object branch of set_parents()
-// against the string's allocation. Setting the type after creating the value
-// avoids this. The warning depends on GCC's inlining decisions, so the
-// sections cover two patterns that trigger it on different GCC versions
-// (#4819 and #5742).
-// On GCC, this file is compiled with -O3 -Werror=array-bounds (see
-// tests/CMakeLists.txt), so the test fails to build if the warning returns.
-
-#include "doctest_compatibility.h"
-
-#ifdef JSON_DIAGNOSTICS
-    #undef JSON_DIAGNOSTICS
-#endif
-
-#define JSON_DIAGNOSTICS 1
-
-#include <nlohmann/json.hpp>
-using nlohmann::json;
-
-#include <algorithm>
-#include <iterator>
-#include <utility>
-#include <vector>
-
-namespace
-{
-enum class diag_color
-{
-    red,
-    green,
-    blue
-};
-
-void to_json(json& j, const diag_color& c)
-{
-    static const std::pair<diag_color, json> m[] = // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
-    {
-        {diag_color::red, "r"},
-        {diag_color::green, "g"},
-        {diag_color::blue, "b"},
-    };
-    const auto* it = std::find_if(std::begin(m), std::end(m), [c](const std::pair<diag_color, json>& p)
-    {
-        return p.first == c;
-    });
-    j = it->second;
-}
-} // namespace
-
-TEST_CASE("diagnostics with optimization")
-{
-    SECTION("issue #4819 - object in vector")
-    {
-        std::vector<json> jsons{};
-        jsons.emplace_back(json({{"key", "value"}}));
-        CHECK(jsons.back()["key"] == "value");
-    }
-
-    SECTION("issue #5742 - string values from a static table")
-    {
-        json j = json::array();
-        j.push_back(diag_color::red);
-        j.push_back(diag_color::green);
-        j.push_back(diag_color::blue);
-        CHECK(j.dump() == R"(["r","g","b"])");
-        CHECK_THROWS_WITH_AS(j[1].get<int>(), "[json.exception.type_error.302] (/1) type must be number, but is string", json::type_error);
-    }
-}

tools/check_build_options/README.md

@@ -0,0 +1,21 @@
+# check_build_options
+
+Checks that the Meson build and the pkg-config files offer the same options as the CMake target, so that a new CMake
+option is not forgotten in one of them.
+
+The compile definitions of the CMake target (`target_compile_definitions` in [`CMakeLists.txt`](../../CMakeLists.txt))
+are the reference. When you add an option there, also add it to
+
+- the pkg-config block in `CMakeLists.txt` (`NLOHMANN_JSON_PKGCONFIG_CFLAGS`),
+- [`meson_options.txt`](../../meson_options.txt), named without the `JSON_` prefix and with the same default,
+- [`meson.build`](../../meson.build) (`json_defines`), and
+- the list of Meson options in
+  [`docs/mkdocs/docs/integration/package_managers.md`](../../docs/mkdocs/docs/integration/package_managers.md).
+
+Run the check with
+
+```shell
+make check_build_options
+```
+
+It needs only Python 3 and runs in the `ci_meson_install` CI job.

tools/check_build_options/check_build_options.py

@@ -0,0 +1,144 @@
+#!/usr/bin/env python3
+"""Check that the Meson build and the pkg-config files offer the CMake options.
+
+The compile definitions of the CMake target (target_compile_definitions in
+CMakeLists.txt) are the reference. For every option used there, the script
+checks that
+
+- the CMake pkg-config file adds the same definition under the same condition,
+- meson_options.txt has a boolean option of the same name without the "JSON_"
+  prefix and with the same default,
+- meson.build adds the same definition under the same condition, and
+- the Meson section of the package manager documentation lists the option.
+
+Meson's MultipleHeaders option selects the include directory and adds no
+definition; it is the only Meson option without a definition.
+"""
+
+import argparse
+import os
+import re
+import sys
+
+REPO_ROOT = os.path.normpath(os.path.join(sys.path[0], '..', '..'))
+DOCS = os.path.join('docs', 'mkdocs', 'docs', 'integration', 'package_managers.md')
+
+# Meson options that add no compile definition, with their default
+MESON_ONLY = {'MultipleHeaders': 'false'}
+
+
+def read(root, path):
+    with open(os.path.join(root, path), encoding='utf-8') as f:
+        return f.read()
+
+
+def cmake_target_definitions(cmake):
+    """Return {option: (definition, add_if_on)} from target_compile_definitions."""
+    block = re.search(r'target_compile_definitions\(\s*\$\{NLOHMANN_JSON_TARGET_NAME\}\s*INTERFACE(.*?)\n\)', cmake, re.S)
+    if not block:
+        sys.exit('CMakeLists.txt: target_compile_definitions of the target not found')
+    result = {}
+    for line in block.group(1).split('\n'):
+        line = line.strip()
+        if not line:
+            continue
+        m = re.fullmatch(r'\$<\$<NOT:\$<BOOL:\$\{JSON_(\w+)\}>>:(\w+=\w+)>', line)
+        if m:
+            result[m.group(1)] = (m.group(2), False)
+            continue
+        m = re.fullmatch(r'\$<\$<BOOL:\$\{JSON_(\w+)\}>:(\w+=\w+)>', line)
+        if m:
+            result[m.group(1)] = (m.group(2), True)
+            continue
+        sys.exit(f'CMakeLists.txt: unexpected line in target_compile_definitions: {line}')
+    return result
+
+
+def cmake_defaults(cmake):
+    """Return {option: 'true'/'false'} for the option() calls of the form JSON_<name>."""
+    return {m.group(1): 'true' if m.group(2) == 'ON' else 'false'
+            for m in re.finditer(r'^option\(JSON_(\w+)\s+"[^"]*"\s+(ON|OFF)\)', cmake, re.M)}
+
+
+def cmake_pkgconfig_definitions(cmake):
+    """Return {option: (definition, add_if_on)} from the pkg-config block."""
+    return {m.group(2): (m.group(3), m.group(1) is None)
+            for m in re.finditer(r'if \((NOT )?JSON_(\w+)\)\s*\n\s*string\(APPEND NLOHMANN_JSON_PKGCONFIG_CFLAGS " -D(\w+=\w+)"\)', cmake)}
+
+
+def meson_options(options):
+    """Return {option: default} for the boolean options in meson_options.txt."""
+    result = {}
+    for block in re.findall(r'option\((.*?)\)', options, re.S):
+        name = re.search(r"'(\w+)'", block).group(1)
+        kind = re.search(r"type\s*:\s*'(\w+)'", block)
+        value = re.search(r'value\s*:\s*(\w+)', block)
+        result[name] = value.group(1) if kind and kind.group(1) == 'boolean' and value else None
+    return result
+
+
+def meson_definitions(meson):
+    """Return {option: (definition, add_if_on)} from meson.build."""
+    return {m.group(2): (m.group(3), m.group(1) is None)
+            for m in re.finditer(r"if (not )?get_option\('(\w+)'\)\s*\n\s*json_defines \+= '(\w+=\w+)'", meson)}
+
+
+def describe(definition):
+    name, add_if_on = definition
+    return f'{name} if {"enabled" if add_if_on else "disabled"}'
+
+
+def compare(errors, where, expected, actual):
+    for option, definition in expected.items():
+        if option not in actual:
+            errors.append(f'{where}: no definition for option {option} (expected {describe(definition)})')
+        elif actual[option] != definition:
+            errors.append(f'{where}: option {option} adds {describe(actual[option])}, expected {describe(definition)}')
+    for option in actual.keys() - expected.keys():
+        errors.append(f'{where}: definition for option {option}, which the CMake target does not have')
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__.split('\n')[0])
+    parser.add_argument('root', nargs='?', default=REPO_ROOT, help='repository root (default: %(default)s)')
+    root = parser.parse_args().root
+
+    cmake = read(root, 'CMakeLists.txt')
+    reference = cmake_target_definitions(cmake)
+    defaults = cmake_defaults(cmake)
+    errors = []
+
+    compare(errors, 'CMakeLists.txt (pkg-config)', reference, cmake_pkgconfig_definitions(cmake))
+    compare(errors, 'meson.build', reference, meson_definitions(read(root, 'meson.build')))
+
+    options = meson_options(read(root, 'meson_options.txt'))
+    for option in reference:
+        if option not in defaults:
+            errors.append(f'CMakeLists.txt: no option(JSON_{option} ... ON|OFF)')
+        elif option not in options:
+            errors.append(f'meson_options.txt: option {option} missing')
+        elif options[option] != defaults[option]:
+            errors.append(f'meson_options.txt: option {option} must be boolean with value {defaults[option]} as in CMake')
+    for option, default in MESON_ONLY.items():
+        if options.get(option) != default:
+            errors.append(f'meson_options.txt: option {option} must be boolean with value {default}')
+    for option in options.keys() - reference.keys() - MESON_ONLY.keys():
+        errors.append(f'meson_options.txt: option {option} has no counterpart in the CMake target')
+
+    docs = read(root, DOCS)
+    for option in sorted(set(options) & (reference.keys() | MESON_ONLY.keys())):
+        if f'`{option}`' not in docs:
+            errors.append(f'{DOCS}: Meson option {option} not listed')
+
+    for error in errors:
+        print(error, file=sys.stderr)
+    if errors:
+        print('The Meson build and the pkg-config files must offer the options of the CMake target; see '
+              'tools/check_build_options/README.md.', file=sys.stderr)
+        return 1
+    print(f'OK: {len(reference)} options with compile definitions agree between CMake, pkg-config, and Meson.')
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main())