Merge branch 'develop' into claude/issue-3885-3dcafd

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

.github/external_ci/appveyor.yml

@@ -83,4 +83,9 @@ build_script:
   - cmake --build . --config "%configuration%" --parallel 2
 
 test_script:
-  - ctest -C "%configuration%" --parallel 2 --output-on-failure
+  - if "%configuration%"=="Release" ctest -C "%configuration%" --parallel 2 --output-on-failure
+  # On Debug builds, skip test-unicode_all
+  # as it is extremely slow to run and cause
+  # occasional timeouts on AppVeyor.
+  # More info: https://github.com/nlohmann/json/pull/1570
+  - if "%configuration%"=="Debug" ctest --exclude-regex "test-unicode" -C "%configuration%" --parallel 2 --output-on-failure

.github/workflows/ubuntu.yml

@@ -31,6 +31,45 @@ 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: 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=${{ github.workspace }}/install-options -DMultipleHeaders=true -DDiagnostics=true -DGlobalUDLs=false
+          meson install -C build-meson-options
+      - name: Check that the options reach the installed files
+        run: |
+          test -d install-options/include/nlohmann/detail
+          cflags=$(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'
+          grep -q 'JSON_USE_GLOBAL_UDLS=0;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:

.github/workflows/windows.yml

@@ -174,7 +174,7 @@ jobs:
       - name: Build
         run: cmake --build build --parallel 10
       - name: Test
-        run: cd build ; ctest -j 10 -C Debug --output-on-failure
+        run: cd build ; ctest -j 10 -C Debug --exclude-regex "test-unicode" --output-on-failure
 
   clang-cl-12:
     runs-on: windows-2022
@@ -191,7 +191,7 @@ jobs:
       - name: Build
         run: cmake --build build --config Debug --parallel 10
       - name: Test
-        run: cd build ; ctest -j 10 -C Debug --output-on-failure
+        run: cd build ; ctest -j 10 -C Debug --exclude-regex "test-unicode" --output-on-failure
 
   ci_module_cpp20:
     runs-on: windows-2022

CMakeLists.txt

@@ -168,7 +168,30 @@ 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_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

@@ -260,9 +260,29 @@ 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`.
+
+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

@@ -222,7 +222,7 @@ 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) BUILD.bazel MODULE.bazel meson.build LICENSE.MIT
+	zip -9 --recurse-paths -X include.zip $(SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_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/ci.cmake

@@ -413,14 +413,13 @@ add_custom_target(ci_test_single_header
 # Valgrind.
 ###############################################################################
 
-# The Unicode test (~17M assertions) is too slow under Valgrind.
 add_custom_target(ci_test_valgrind
     COMMAND CXX=${GCC_TOOL} ${CMAKE_COMMAND}
         -DCMAKE_BUILD_TYPE=Debug -GNinja
         -DJSON_BuildTests=ON -DJSON_Valgrind=ON
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_valgrind
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_valgrind
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_valgrind && ${CMAKE_CTEST_COMMAND} -L valgrind --exclude-regex "test-unicode" --parallel ${N} --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_valgrind && ${CMAKE_CTEST_COMMAND} -L valgrind --parallel ${N} --output-on-failure
     COMMENT "Compile and test with Valgrind"
 )
 
@@ -718,7 +717,7 @@ foreach(COMPILER g++-4.8 g++-4.9 g++-5 g++-6 g++-7 g++-8 g++-9 g++-10 g++-11 cla
                 -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_compiler_${COMPILER}
                 ${ADDITIONAL_FLAGS}
             COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_compiler_${COMPILER}
-            COMMAND cd ${PROJECT_BINARY_DIR}/build_compiler_${COMPILER} && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
+            COMMAND cd ${PROJECT_BINARY_DIR}/build_compiler_${COMPILER} && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode" --output-on-failure
             COMMENT "Compile and test with ${COMPILER}"
         )
     endif()
@@ -732,7 +731,7 @@ add_custom_target(ci_test_compiler_default
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_compiler_default
         ${ADDITIONAL_FLAGS}
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_compiler_default --parallel ${N}
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_compiler_default && ${CMAKE_CTEST_COMMAND} --parallel ${N} -LE git_required --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_compiler_default && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode" -LE git_required --output-on-failure
     COMMENT "Compile and test with default C++ compiler"
 )
 
@@ -770,7 +769,7 @@ add_custom_target(ci_icpc
         -DJSON_BuildTests=ON -DJSON_FastTests=ON
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_icpc
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_icpc
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_icpc && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_icpc && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode" --output-on-failure
     COMMENT "Compile and test with ICPC"
 )
 
@@ -781,7 +780,7 @@ add_custom_target(ci_icpx
         -DJSON_BuildTests=ON -DJSON_FastTests=ON
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_icpx
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_icpx
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_icpx && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_icpx && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode" --output-on-failure
     COMMENT "Compile and test with ICPX (Intel oneAPI DPC++/C++)"
 )
 
@@ -817,7 +816,7 @@ add_custom_target(ci_nvhpc
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_nvhpc
     # the pipes are escaped so the surrounding shell passes them to ctest verbatim
     # instead of treating them as shell pipe operators
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_nvhpc && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-comparison_cpp20\\|test-comparison_legacy_cpp20\\|test-constructor1_cpp11\\|test-deserialization_cpp20" --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_nvhpc && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode\\|test-comparison_cpp20\\|test-comparison_legacy_cpp20\\|test-constructor1_cpp11\\|test-deserialization_cpp20" --output-on-failure
     COMMENT "Compile and test with NVIDIA HPC SDK (nvc++)"
 )
 

cmake/nlohmann_jsonTargets.cmake.in

@@ -0,0 +1,38 @@
+# 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 "${CMAKE_CURRENT_LIST_DIR}/@NLOHMANN_JSON_CONFIG_TO_PREFIX@" ABSOLUTE)
+
+add_library(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ INTERFACE IMPORTED)
+set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+    INTERFACE_INCLUDE_DIRECTORIES "@NLOHMANN_JSON_INCLUDE_DIR@"
+)
+if(CMAKE_VERSION VERSION_LESS 3.8)
+    set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+        INTERFACE_COMPILE_FEATURES cxx_range_for
+    )
+else()
+    set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+        INTERFACE_COMPILE_FEATURES cxx_std_11
+    )
+endif()
+
+set(_NLOHMANN_JSON_COMPILE_DEFINITIONS "@NLOHMANN_JSON_COMPILE_DEFINITIONS@")
+if(_NLOHMANN_JSON_COMPILE_DEFINITIONS)
+    set_target_properties(@PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+        INTERFACE_COMPILE_DEFINITIONS "${_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

@@ -121,10 +121,23 @@ 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 file is installed. To use it, have your build system require the `nlohmann_json`
-pkg-config dependency. In Meson, it is preferred to use the
-[`dependency()`](https://mesonbuild.com/Reference-manual.html#dependency) object with a subproject fallback, rather than
-using the subproject directly.
+which case a pkg-config file and the CMake package config files are installed. To use it, have your build system require
+the `nlohmann_json` pkg-config dependency, or use [`find_package(nlohmann_json)`](cmake.md#external) in CMake. In Meson,
+it is preferred to use the [`dependency()`](https://mesonbuild.com/Reference-manual.html#dependency) object with a
+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`, `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"
 

meson.build

@@ -2,23 +2,111 @@ 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('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_headers('single_include/nlohmann/json_fwd.hpp', subdir: 'nlohmann')
+    install_subdir(
+        incdir / 'nlohmann',
+        install_dir: get_option('includedir'),
+        install_tag: 'devel',
+    )
 
-pkgc = import('pkgconfig')
-pkgc.generate(name: 'nlohmann_json',
-    version: meson.project_version(),
-    description: 'JSON for Modern C++'
-)
+    pkgc = import('pkgconfig')
+    pkgc.generate(name: 'nlohmann_json',
+        version: meson.project_version(),
+        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 +1,48 @@
+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(
+    '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',
+)

tests/CMakeLists.txt

@@ -129,6 +129,9 @@ json_test_set_test_options(test-disabled_exceptions
         #$<$<CXX_COMPILER_ID:MSVC>:/EH>
 )
 
+# raise timeout of expensive Unicode test
+json_test_set_test_options(test-unicode4 TEST_PROPERTIES TIMEOUT 3000)
+
 #############################################################################
 # add unit tests
 #############################################################################

tests/src/test_utils.hpp

@@ -8,7 +8,6 @@
 
 #pragma once
 
-#include <array> // array
 #include <cstdint> // uint8_t
 #include <cstddef> // size_t
 #include <fstream> // ifstream, istreambuf_iterator, ios
@@ -43,33 +42,6 @@ T next_integer_sample(T i, T last, T stride)
     return n < last ? n : last;
 }
 
-// UTF-8 continuation bytes in [lo, hi] that stand in for all of them in the
-// ill-formed UTF-8 tests. Both the lexer's range checks and the serializer's
-// decoder (detail::decode) only distinguish the classes 0x80..0x8F, 0x90..0x9F,
-// and 0xA0..0xBF, so the first and last byte of each class within [lo, hi]
-// exercise every behavior while a test sweeps another byte position through
-// all 256 values (#5418). Define JSON_TEST_UTF8_EXHAUSTIVE to get every byte.
-inline std::vector<int> utf8_continuation_bytes(int lo, int hi)
-{
-    std::vector<int> result;
-#ifdef JSON_TEST_UTF8_EXHAUSTIVE
-    for (int byte = lo; byte <= hi; ++byte)
-    {
-        result.push_back(byte);
-    }
-#else
-    static const std::array<int, 6> class_ends = {{0x80, 0x8F, 0x90, 0x9F, 0xA0, 0xBF}};
-    for (const int byte : class_ends)
-    {
-        if (lo <= byte && byte <= hi)
-        {
-            result.push_back(byte);
-        }
-    }
-#endif
-    return result;
-}
-
 inline std::vector<std::uint8_t> read_binary_file(const std::string& filename)
 {
     std::ifstream file(filename, std::ios::binary);

tests/src/unit-binary_formats.cpp

@@ -14,7 +14,7 @@ using nlohmann::json;
 #include <fstream>
 #include "make_test_data_available.hpp"
 
-TEST_CASE("Binary Formats")
+TEST_CASE("Binary Formats" * doctest::skip())
 {
     SECTION("canada.json")
     {
@@ -142,6 +142,48 @@ TEST_CASE("Binary Formats")
         CHECK((100.0 * double(ubjson_3_size) / double(json_size)) == Approx(84.963));
     }
 
+    SECTION("jeopardy.json")
+    {
+        const auto* filename = TEST_DATA_DIRECTORY "/jeopardy/jeopardy.json";
+        json j = json::parse(std::ifstream(filename));
+
+        const auto json_size = j.dump().size();
+        const auto bjdata_1_size = json::to_bjdata(j).size();
+        const auto bjdata_2_size = json::to_bjdata(j, true).size();
+        const auto bjdata_3_size = json::to_bjdata(j, true, true).size();
+        const auto bon8_size = json::to_bon8(j).size();
+        const auto bson_size = json::to_bson({{"", j}}).size(); // wrap array in object for BSON
+        const auto cbor_size = json::to_cbor(j).size();
+        const auto msgpack_size = json::to_msgpack(j).size();
+        const auto ubjson_1_size = json::to_ubjson(j).size();
+        const auto ubjson_2_size = json::to_ubjson(j, true).size();
+        const auto ubjson_3_size = json::to_ubjson(j, true, true).size();
+
+        CHECK(json_size == 52508728);
+        CHECK(bjdata_1_size == 50710965);
+        CHECK(bjdata_2_size == 51144830);
+        CHECK(bjdata_3_size == 51144830);
+        CHECK(bon8_size == 45942080);
+        CHECK(bson_size == 56008520);
+        CHECK(cbor_size == 46187320);
+        CHECK(msgpack_size == 46158575);
+        CHECK(ubjson_1_size == 50710965);
+        CHECK(ubjson_2_size == 51144830);
+        CHECK(ubjson_3_size == 49861422);
+
+        CHECK((100.0 * double(json_size) / double(json_size)) == Approx(100.0));
+        CHECK((100.0 * double(bjdata_1_size) / double(json_size)) == Approx(96.576));
+        CHECK((100.0 * double(bjdata_2_size) / double(json_size)) == Approx(97.402));
+        CHECK((100.0 * double(bjdata_3_size) / double(json_size)) == Approx(97.402));
+        CHECK((100.0 * double(bon8_size) / double(json_size)) == Approx(87.494));
+        CHECK((100.0 * double(bson_size) / double(json_size)) == Approx(106.665));
+        CHECK((100.0 * double(cbor_size) / double(json_size)) == Approx(87.961));
+        CHECK((100.0 * double(msgpack_size) / double(json_size)) == Approx(87.906));
+        CHECK((100.0 * double(ubjson_1_size) / double(json_size)) == Approx(96.576));
+        CHECK((100.0 * double(ubjson_2_size) / double(json_size)) == Approx(97.402));
+        CHECK((100.0 * double(ubjson_3_size) / double(json_size)) == Approx(94.958));
+    }
+
     SECTION("sample.json")
     {
         const auto* filename = TEST_DATA_DIRECTORY "/json_testsuite/sample.json";
@@ -182,47 +224,3 @@ TEST_CASE("Binary Formats")
         CHECK((100.0 * double(ubjson_3_size) / double(json_size)) == Approx(89.450));
     }
 }
-
-// jeopardy.json is 52 MB and produces ~500 MB of serialization output, so it
-// is kept apart from the cheap corpus files above (#5418)
-TEST_CASE("Binary Formats (jeopardy.json)" * doctest::skip())
-{
-    const auto* filename = TEST_DATA_DIRECTORY "/jeopardy/jeopardy.json";
-    json j = json::parse(std::ifstream(filename));
-
-    const auto json_size = j.dump().size();
-    const auto bjdata_1_size = json::to_bjdata(j).size();
-    const auto bjdata_2_size = json::to_bjdata(j, true).size();
-    const auto bjdata_3_size = json::to_bjdata(j, true, true).size();
-    const auto bon8_size = json::to_bon8(j).size();
-    const auto bson_size = json::to_bson({{"", j}}).size(); // wrap array in object for BSON
-    const auto cbor_size = json::to_cbor(j).size();
-    const auto msgpack_size = json::to_msgpack(j).size();
-    const auto ubjson_1_size = json::to_ubjson(j).size();
-    const auto ubjson_2_size = json::to_ubjson(j, true).size();
-    const auto ubjson_3_size = json::to_ubjson(j, true, true).size();
-
-    CHECK(json_size == 52508728);
-    CHECK(bjdata_1_size == 50710965);
-    CHECK(bjdata_2_size == 51144830);
-    CHECK(bjdata_3_size == 51144830);
-    CHECK(bon8_size == 45942080);
-    CHECK(bson_size == 56008520);
-    CHECK(cbor_size == 46187320);
-    CHECK(msgpack_size == 46158575);
-    CHECK(ubjson_1_size == 50710965);
-    CHECK(ubjson_2_size == 51144830);
-    CHECK(ubjson_3_size == 49861422);
-
-    CHECK((100.0 * double(json_size) / double(json_size)) == Approx(100.0));
-    CHECK((100.0 * double(bjdata_1_size) / double(json_size)) == Approx(96.576));
-    CHECK((100.0 * double(bjdata_2_size) / double(json_size)) == Approx(97.402));
-    CHECK((100.0 * double(bjdata_3_size) / double(json_size)) == Approx(97.402));
-    CHECK((100.0 * double(bon8_size) / double(json_size)) == Approx(87.494));
-    CHECK((100.0 * double(bson_size) / double(json_size)) == Approx(106.665));
-    CHECK((100.0 * double(cbor_size) / double(json_size)) == Approx(87.961));
-    CHECK((100.0 * double(msgpack_size) / double(json_size)) == Approx(87.906));
-    CHECK((100.0 * double(ubjson_1_size) / double(json_size)) == Approx(96.576));
-    CHECK((100.0 * double(ubjson_2_size) / double(json_size)) == Approx(97.402));
-    CHECK((100.0 * double(ubjson_3_size) / double(json_size)) == Approx(94.958));
-}

tests/src/unit-msgpack-cpp17.cpp

@@ -1,99 +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
-
-// This file contains the C++17-only part of unit-msgpack.cpp (std::byte
-// input). It is kept in a separate translation unit so the (much larger)
-// unit-msgpack.cpp does not need to be compiled and run a second time just
-// for this one test case (#5418).
-
-#include "doctest_compatibility.h"
-
-#include <nlohmann/json.hpp>
-using nlohmann::json;
-
-#ifdef JSON_HAS_CPP_17
-#include <cstddef>
-#include <vector>
-
-// Test suite for verifying MessagePack handling with std::byte input
-TEST_CASE("MessagePack with std::byte")
-{
-
-    SECTION("std::byte compatibility")
-    {
-        SECTION("vector roundtrip")
-        {
-            json original =
-            {
-                {"name", "test"},
-                {"value", 42},
-                {"array", {1, 2, 3}}
-            };
-
-            std::vector<uint8_t> temp = json::to_msgpack(original);
-            // Convert the uint8_t vector to std::byte vector
-            std::vector<std::byte> msgpack_data(temp.size());
-            for (size_t i = 0; i < temp.size(); ++i)
-            {
-                msgpack_data[i] = std::byte(temp[i]);
-            }
-            // Deserialize from std::byte vector back to JSON
-            json from_bytes;
-            CHECK_NOTHROW(from_bytes = json::from_msgpack(msgpack_data));
-
-            CHECK(from_bytes == original);
-        }
-
-        SECTION("empty vector")
-        {
-            const std::vector<std::byte> empty_data;
-            CHECK_THROWS_WITH_AS([&]()
-            {
-                [[maybe_unused]] auto result = json::from_msgpack(empty_data);
-                return true;
-            }
-            (),
-            "[json.exception.parse_error.110] parse error at byte 1: syntax error while parsing MessagePack value: unexpected end of input",
-            json::parse_error&);
-        }
-
-        SECTION("comparison with workaround")
-        {
-            json original =
-            {
-                {"string", "hello"},
-                {"integer", 42},
-                {"float", 3.14},
-                {"boolean", true},
-                {"null", nullptr},
-                {"array", {1, 2, 3}},
-                {"object", {{"key", "value"}}}
-            };
-
-            std::vector<uint8_t> temp = json::to_msgpack(original);
-
-            std::vector<std::byte> msgpack_data(temp.size());
-            for (size_t i = 0; i < temp.size(); ++i)
-            {
-                msgpack_data[i] = std::byte(temp[i]);
-            }
-            // Attempt direct deserialization using std::byte input
-            const json direct_result = json::from_msgpack(msgpack_data);
-
-            // Test the workaround approach: reinterpret as unsigned char* and use iterator range
-            const auto* const char_start = reinterpret_cast<unsigned char const*>(msgpack_data.data());
-            const auto* const char_end = char_start + msgpack_data.size();
-            json workaround_result = json::from_msgpack(char_start, char_end);
-
-            // Verify that the final deserialized JSON matches the original JSON
-            CHECK(direct_result == workaround_result);
-            CHECK(direct_result == original);
-        }
-    }
-}
-#endif

tests/src/unit-msgpack.cpp

@@ -2085,6 +2085,85 @@ TEST_CASE("MessagePack roundtrips" * doctest::skip())
     }
 }
 
+#ifdef JSON_HAS_CPP_17
+// Test suite for verifying MessagePack handling with std::byte input
+TEST_CASE("MessagePack with std::byte")
+{
+
+    SECTION("std::byte compatibility")
+    {
+        SECTION("vector roundtrip")
+        {
+            json original =
+            {
+                {"name", "test"},
+                {"value", 42},
+                {"array", {1, 2, 3}}
+            };
+
+            std::vector<uint8_t> temp = json::to_msgpack(original);
+            // Convert the uint8_t vector to std::byte vector
+            std::vector<std::byte> msgpack_data(temp.size());
+            for (size_t i = 0; i < temp.size(); ++i)
+            {
+                msgpack_data[i] = std::byte(temp[i]);
+            }
+            // Deserialize from std::byte vector back to JSON
+            json from_bytes;
+            CHECK_NOTHROW(from_bytes = json::from_msgpack(msgpack_data));
+
+            CHECK(from_bytes == original);
+        }
+
+        SECTION("empty vector")
+        {
+            const std::vector<std::byte> empty_data;
+            CHECK_THROWS_WITH_AS([&]()
+            {
+                [[maybe_unused]] auto result = json::from_msgpack(empty_data);
+                return true;
+            }
+            (),
+            "[json.exception.parse_error.110] parse error at byte 1: syntax error while parsing MessagePack value: unexpected end of input",
+            json::parse_error&);
+        }
+
+        SECTION("comparison with workaround")
+        {
+            json original =
+            {
+                {"string", "hello"},
+                {"integer", 42},
+                {"float", 3.14},
+                {"boolean", true},
+                {"null", nullptr},
+                {"array", {1, 2, 3}},
+                {"object", {{"key", "value"}}}
+            };
+
+            std::vector<uint8_t> temp = json::to_msgpack(original);
+
+            std::vector<std::byte> msgpack_data(temp.size());
+            for (size_t i = 0; i < temp.size(); ++i)
+            {
+                msgpack_data[i] = std::byte(temp[i]);
+            }
+            // Attempt direct deserialization using std::byte input
+            const json direct_result = json::from_msgpack(msgpack_data);
+
+            // Test the workaround approach: reinterpret as unsigned char* and use iterator range
+            const auto* const char_start = reinterpret_cast<unsigned char const*>(msgpack_data.data());
+            const auto* const char_end = char_start + msgpack_data.size();
+            json workaround_result = json::from_msgpack(char_start, char_end);
+
+            // Verify that the final deserialized JSON matches the original JSON
+            CHECK(direct_result == workaround_result);
+            CHECK(direct_result == original);
+        }
+    }
+}
+#endif
+
 // the fake sizes below do not fit into a 32-bit std::size_t
 // with clang and libstdc++ 10, the std::filesystem::path conversion that
 // C++17 builds consider for every string type is ambiguous for a class

tests/src/unit-unicode1.cpp

@@ -0,0 +1,623 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+// for some reason including this after the json header leads to linker errors with VS 2017...
+#include <locale>
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <fstream>
+#include <sstream>
+#include <iomanip>
+#include "make_test_data_available.hpp"
+#include "test_utils.hpp"
+
+TEST_CASE("Unicode (1/5)" * doctest::skip())
+{
+    SECTION("\\uxxxx sequences")
+    {
+        // create an escaped string from a code point
+        const auto codepoint_to_unicode = [](std::size_t cp)
+        {
+            // code points are represented as a six-character sequence: a
+            // reverse solidus, followed by the lowercase letter u, followed
+            // by four hexadecimal digits that encode the character's code
+            // point
+            std::stringstream ss;
+            ss << "\\u" << std::setw(4) << std::setfill('0') << std::hex << cp;
+            return ss.str();
+        };
+
+        SECTION("correct sequences")
+        {
+            // generate all UTF-8 code points; in total, 1112064 code points are
+            // generated: 0x1FFFFF code points - 2048 invalid values between
+            // 0xD800 and 0xDFFF.
+            for (std::size_t cp = 0; cp <= 0x10FFFFu; ++cp)
+            {
+                // string to store the code point as in \uxxxx format
+                std::string json_text = "\"";
+
+                // decide whether to use one or two \uxxxx sequences
+                if (cp < 0x10000u)
+                {
+                    // The Unicode standard permanently reserves these code point
+                    // values for UTF-16 encoding of the high and low surrogates, and
+                    // they will never be assigned a character, so there should be no
+                    // reason to encode them. The official Unicode standard says that
+                    // no UTF forms, including UTF-16, can encode these code points.
+                    if (cp >= 0xD800u && cp <= 0xDFFFu)
+                    {
+                        // if we would not skip these code points, we would get a
+                        // "missing low surrogate" exception
+                        continue;
+                    }
+
+                    // code points in the Basic Multilingual Plane can be
+                    // represented with one \uxxxx sequence
+                    json_text += codepoint_to_unicode(cp);
+                }
+                else
+                {
+                    // To escape an extended character that is not in the Basic
+                    // Multilingual Plane, the character is represented as a
+                    // 12-character sequence, encoding the UTF-16 surrogate pair
+                    const auto codepoint1 = 0xd800u + (((cp - 0x10000u) >> 10) & 0x3ffu);
+                    const auto codepoint2 = 0xdc00u + ((cp - 0x10000u) & 0x3ffu);
+                    json_text += codepoint_to_unicode(codepoint1) + codepoint_to_unicode(codepoint2);
+                }
+
+                json_text += "\"";
+                CAPTURE(json_text)
+                json _;
+                CHECK_NOTHROW(_ = json::parse(json_text));
+            }
+        }
+
+        SECTION("incorrect sequences")
+        {
+            SECTION("incorrect surrogate values")
+            {
+                json _;
+
+                CHECK_THROWS_WITH_AS(_ = json::parse("\"\\uDC00\\uDC00\""), "[json.exception.parse_error.101] parse error at line 1, column 7: syntax error while parsing value - invalid string: surrogate U+DC00..U+DFFF must follow U+D800..U+DBFF; last read: '\"\\uDC00'", json::parse_error&);
+
+                CHECK_THROWS_WITH_AS(_ = json::parse("\"\\uD7FF\\uDC00\""), "[json.exception.parse_error.101] parse error at line 1, column 13: syntax error while parsing value - invalid string: surrogate U+DC00..U+DFFF must follow U+D800..U+DBFF; last read: '\"\\uD7FF\\uDC00'", json::parse_error&);
+
+                CHECK_THROWS_WITH_AS(_ = json::parse("\"\\uD800]\""), "[json.exception.parse_error.101] parse error at line 1, column 8: syntax error while parsing value - invalid string: surrogate U+D800..U+DBFF must be followed by U+DC00..U+DFFF; last read: '\"\\uD800]'", json::parse_error&);
+
+                CHECK_THROWS_WITH_AS(_ = json::parse("\"\\uD800\\v\""), "[json.exception.parse_error.101] parse error at line 1, column 9: syntax error while parsing value - invalid string: surrogate U+D800..U+DBFF must be followed by U+DC00..U+DFFF; last read: '\"\\uD800\\v'", json::parse_error&);
+
+                CHECK_THROWS_WITH_AS(_ = json::parse("\"\\uD800\\u123\""), "[json.exception.parse_error.101] parse error at line 1, column 13: syntax error while parsing value - invalid string: '\\u' must be followed by 4 hex digits; last read: '\"\\uD800\\u123\"'", json::parse_error&);
+
+                CHECK_THROWS_WITH_AS(_ = json::parse("\"\\uD800\\uDBFF\""), "[json.exception.parse_error.101] parse error at line 1, column 13: syntax error while parsing value - invalid string: surrogate U+D800..U+DBFF must be followed by U+DC00..U+DFFF; last read: '\"\\uD800\\uDBFF'", json::parse_error&);
+
+                CHECK_THROWS_WITH_AS(_ = json::parse("\"\\uD800\\uE000\""), "[json.exception.parse_error.101] parse error at line 1, column 13: syntax error while parsing value - invalid string: surrogate U+D800..U+DBFF must be followed by U+DC00..U+DFFF; last read: '\"\\uD800\\uE000'", json::parse_error&);
+            }
+        }
+
+#if 0 // NOLINT(readability-avoid-unconditional-preprocessor-if)
+        SECTION("incorrect sequences")
+        {
+            SECTION("high surrogate without low surrogate")
+            {
+                // D800..DBFF are high surrogates and must be followed by low
+                // surrogates DC00..DFFF; here, nothing follows
+                for (std::size_t cp = 0xD800u; cp <= 0xDBFFu; ++cp)
+                {
+                    std::string json_text = "\"" + codepoint_to_unicode(cp) + "\"";
+                    CAPTURE(json_text)
+                    CHECK_THROWS_AS(json::parse(json_text), json::parse_error&);
+                }
+            }
+
+            SECTION("high surrogate with wrong low surrogate")
+            {
+                // D800..DBFF are high surrogates and must be followed by low
+                // surrogates DC00..DFFF; here a different sequence follows
+                for (std::size_t cp1 = 0xD800u; cp1 <= 0xDBFFu; ++cp1)
+                {
+                    for (std::size_t cp2 = 0x0000u; cp2 <= 0xFFFFu; ++cp2)
+                    {
+                        if (0xDC00u <= cp2 && cp2 <= 0xDFFFu)
+                        {
+                            continue;
+                        }
+
+                        std::string json_text = "\"" + codepoint_to_unicode(cp1) + codepoint_to_unicode(cp2) + "\"";
+                        CAPTURE(json_text)
+                        CHECK_THROWS_AS(json::parse(json_text), json::parse_error&);
+                    }
+                }
+            }
+
+            SECTION("low surrogate without high surrogate")
+            {
+                // low surrogates DC00..DFFF must follow high surrogates; here,
+                // they occur alone
+                for (std::size_t cp = 0xDC00u; cp <= 0xDFFFu; ++cp)
+                {
+                    std::string json_text = "\"" + codepoint_to_unicode(cp) + "\"";
+                    CAPTURE(json_text)
+                    CHECK_THROWS_AS(json::parse(json_text), json::parse_error&);
+                }
+            }
+
+        }
+#endif
+    }
+
+    SECTION("read all unicode characters")
+    {
+        // read a file with all Unicode characters stored as single-character
+        // strings in a JSON array
+        std::ifstream f(TEST_DATA_DIRECTORY "/json_nlohmann_tests/all_unicode.json");
+        json j;
+        CHECK_NOTHROW(f >> j);
+
+        // the array has 1112064 + 1 elements (a terminating "null" value)
+        // Note: 1112064 = 0x1FFFFF code points - 2048 invalid values between
+        // 0xD800 and 0xDFFF.
+        CHECK(j.size() == 1112065);
+
+        SECTION("check JSON Pointers")
+        {
+            for (const auto& s : j)
+            {
+                // skip non-string JSON values
+                if (!s.is_string())
+                {
+                    continue;
+                }
+
+                auto ptr = s.get<std::string>();
+
+                // tilde must be followed by 0 or 1
+                if (ptr == "~")
+                {
+                    ptr += "0";
+                }
+
+                // JSON Pointers must begin with "/"
+                ptr.insert(0, "/");
+
+                CHECK_NOTHROW(json::json_pointer("/" + ptr));
+
+                // check escape/unescape roundtrip
+                auto escaped = nlohmann::detail::escape(ptr);
+                nlohmann::detail::unescape(escaped);
+                CHECK(escaped == ptr);
+            }
+        }
+    }
+
+    SECTION("ignore byte-order-mark")
+    {
+        SECTION("in a stream")
+        {
+            // read a file with a UTF-8 BOM
+            std::ifstream f(TEST_DATA_DIRECTORY "/json_nlohmann_tests/bom.json");
+            json j;
+            CHECK_NOTHROW(f >> j);
+        }
+
+        SECTION("with an iterator")
+        {
+            std::string i = "\xef\xbb\xbf{\n   \"foo\": true\n}";
+            json _;
+            CHECK_NOTHROW(_ = json::parse(i.begin(), i.end()));
+        }
+    }
+
+    SECTION("error for incomplete/wrong BOM")
+    {
+        json _;
+        CHECK_THROWS_AS(_ = json::parse("\xef\xbb"), json::parse_error&);
+        CHECK_THROWS_AS(_ = json::parse("\xef\xbb\xbb"), json::parse_error&);
+    }
+}
+
+namespace
+{
+void roundtrip(bool success_expected, const std::string& s);
+
+void roundtrip(bool success_expected, const std::string& s)
+{
+    CAPTURE(s)
+    json _;
+
+    // create JSON string value
+    const json j = s;
+    // create JSON text
+    const std::string ps = std::string("\"") + s + "\"";
+
+    if (success_expected)
+    {
+        // serialization succeeds
+        // dump() is nodiscard; this only checks that dumping does not throw
+        CHECK_NOTHROW(utils::ignore_return_value(j.dump()));
+
+        // exclude parse test for U+0000
+        if (s[0] != '\0')
+        {
+            // parsing JSON text succeeds
+            CHECK_NOTHROW(_ = json::parse(ps));
+        }
+
+        // roundtrip succeeds
+        CHECK_NOTHROW(_ = json::parse(j.dump()));
+
+        // after roundtrip, the same string is stored
+        const json jr = json::parse(j.dump());
+        CHECK(jr.get<std::string>() == s);
+    }
+    else
+    {
+        // serialization fails
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
+
+        // parsing JSON text fails
+        CHECK_THROWS_AS(_ = json::parse(ps), json::parse_error&);
+    }
+}
+} // namespace
+
+TEST_CASE("Markus Kuhn's UTF-8 decoder capability and stress test")
+{
+    // Markus Kuhn <http://www.cl.cam.ac.uk/~mgk25/> - 2015-08-28 - CC BY 4.0
+    // http://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-test.txt
+
+    SECTION("1  Some correct UTF-8 text")
+    {
+        roundtrip(true, "κόσμε");
+    }
+
+    SECTION("2  Boundary condition test cases")
+    {
+        SECTION("2.1  First possible sequence of a certain length")
+        {
+            // 2.1.1  1 byte  (U-00000000)
+            roundtrip(true, std::string("\0", 1));
+            // 2.1.2  2 bytes (U-00000080)
+            roundtrip(true, "\xc2\x80");
+            // 2.1.3  3 bytes (U-00000800)
+            roundtrip(true, "\xe0\xa0\x80");
+            // 2.1.4  4 bytes (U-00010000)
+            roundtrip(true, "\xf0\x90\x80\x80");
+
+            // 2.1.5  5 bytes (U-00200000)
+            roundtrip(false, "\xF8\x88\x80\x80\x80");
+            // 2.1.6  6 bytes (U-04000000)
+            roundtrip(false, "\xFC\x84\x80\x80\x80\x80");
+        }
+
+        SECTION("2.2  Last possible sequence of a certain length")
+        {
+            // 2.2.1  1 byte  (U-0000007F)
+            roundtrip(true, "\x7f");
+            // 2.2.2  2 bytes (U-000007FF)
+            roundtrip(true, "\xdf\xbf");
+            // 2.2.3  3 bytes (U-0000FFFF)
+            roundtrip(true, "\xef\xbf\xbf");
+
+            // 2.2.4  4 bytes (U-001FFFFF)
+            roundtrip(false, "\xF7\xBF\xBF\xBF");
+            // 2.2.5  5 bytes (U-03FFFFFF)
+            roundtrip(false, "\xFB\xBF\xBF\xBF\xBF");
+            // 2.2.6  6 bytes (U-7FFFFFFF)
+            roundtrip(false, "\xFD\xBF\xBF\xBF\xBF\xBF");
+        }
+
+        SECTION("2.3  Other boundary conditions")
+        {
+            // 2.3.1  U-0000D7FF = ed 9f bf
+            roundtrip(true, "\xed\x9f\xbf");
+            // 2.3.2  U-0000E000 = ee 80 80
+            roundtrip(true, "\xee\x80\x80");
+            // 2.3.3  U-0000FFFD = ef bf bd
+            roundtrip(true, "\xef\xbf\xbd");
+            // 2.3.4  U-0010FFFF = f4 8f bf bf
+            roundtrip(true, "\xf4\x8f\xbf\xbf");
+
+            // 2.3.5  U-00110000 = f4 90 80 80
+            roundtrip(false, "\xf4\x90\x80\x80");
+        }
+    }
+
+    SECTION("3  Malformed sequences")
+    {
+        SECTION("3.1  Unexpected continuation bytes")
+        {
+            // Each unexpected continuation byte should be separately signalled as a
+            // malformed sequence of its own.
+
+            // 3.1.1  First continuation byte 0x80
+            roundtrip(false, "\x80");
+            // 3.1.2  Last  continuation byte 0xbf
+            roundtrip(false, "\xbf");
+
+            // 3.1.3  2 continuation bytes
+            roundtrip(false, "\x80\xbf");
+            // 3.1.4  3 continuation bytes
+            roundtrip(false, "\x80\xbf\x80");
+            // 3.1.5  4 continuation bytes
+            roundtrip(false, "\x80\xbf\x80\xbf");
+            // 3.1.6  5 continuation bytes
+            roundtrip(false, "\x80\xbf\x80\xbf\x80");
+            // 3.1.7  6 continuation bytes
+            roundtrip(false, "\x80\xbf\x80\xbf\x80\xbf");
+            // 3.1.8  7 continuation bytes
+            roundtrip(false, "\x80\xbf\x80\xbf\x80\xbf\x80");
+
+            // 3.1.9  Sequence of all 64 possible continuation bytes (0x80-0xbf)
+            roundtrip(false, "\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf");
+        }
+
+        SECTION("3.2  Lonely start characters")
+        {
+            // 3.2.1  All 32 first bytes of 2-byte sequences (0xc0-0xdf)
+            roundtrip(false, "\xc0 \xc1 \xc2 \xc3 \xc4 \xc5 \xc6 \xc7 \xc8 \xc9 \xca \xcb \xcc \xcd \xce \xcf \xd0 \xd1 \xd2 \xd3 \xd4 \xd5 \xd6 \xd7 \xd8 \xd9 \xda \xdb \xdc \xdd \xde \xdf");
+            // 3.2.2  All 16 first bytes of 3-byte sequences (0xe0-0xef)
+            roundtrip(false, "\xe0 \xe1 \xe2 \xe3 \xe4 \xe5 \xe6 \xe7 \xe8 \xe9 \xea \xeb \xec \xed \xee \xef");
+            // 3.2.3  All 8 first bytes of 4-byte sequences (0xf0-0xf7)
+            roundtrip(false, "\xf0 \xf1 \xf2 \xf3 \xf4 \xf5 \xf6 \xf7");
+            // 3.2.4  All 4 first bytes of 5-byte sequences (0xf8-0xfb)
+            roundtrip(false, "\xf8 \xf9 \xfa \xfb");
+            // 3.2.5  All 2 first bytes of 6-byte sequences (0xfc-0xfd)
+            roundtrip(false, "\xfc \xfd");
+        }
+
+        SECTION("3.3  Sequences with last continuation byte missing")
+        {
+            // All bytes of an incomplete sequence should be signalled as a single
+            // malformed sequence, i.e., you should see only a single replacement
+            // character in each of the next 10 tests. (Characters as in section 2)
+
+            // 3.3.1  2-byte sequence with last byte missing (U+0000)
+            roundtrip(false, "\xc0");
+            // 3.3.2  3-byte sequence with last byte missing (U+0000)
+            roundtrip(false, "\xe0\x80");
+            // 3.3.3  4-byte sequence with last byte missing (U+0000)
+            roundtrip(false, "\xf0\x80\x80");
+            // 3.3.4  5-byte sequence with last byte missing (U+0000)
+            roundtrip(false, "\xf8\x80\x80\x80");
+            // 3.3.5  6-byte sequence with last byte missing (U+0000)
+            roundtrip(false, "\xfc\x80\x80\x80\x80");
+            // 3.3.6  2-byte sequence with last byte missing (U-000007FF)
+            roundtrip(false, "\xdf");
+            // 3.3.7  3-byte sequence with last byte missing (U-0000FFFF)
+            roundtrip(false, "\xef\xbf");
+            // 3.3.8  4-byte sequence with last byte missing (U-001FFFFF)
+            roundtrip(false, "\xf7\xbf\xbf");
+            // 3.3.9  5-byte sequence with last byte missing (U-03FFFFFF)
+            roundtrip(false, "\xfb\xbf\xbf\xbf");
+            // 3.3.10 6-byte sequence with last byte missing (U-7FFFFFFF)
+            roundtrip(false, "\xfd\xbf\xbf\xbf\xbf");
+        }
+
+        SECTION("3.4  Concatenation of incomplete sequences")
+        {
+            // All the 10 sequences of 3.3 concatenated, you should see 10 malformed
+            // sequences being signalled:
+            roundtrip(false, "\xc0\xe0\x80\xf0\x80\x80\xf8\x80\x80\x80\xfc\x80\x80\x80\x80\xdf\xef\xbf\xf7\xbf\xbf\xfb\xbf\xbf\xbf\xfd\xbf\xbf\xbf\xbf");
+        }
+
+        SECTION("3.5  Impossible bytes")
+        {
+            // The following two bytes cannot appear in a correct UTF-8 string
+
+            // 3.5.1  fe
+            roundtrip(false, "\xfe");
+            // 3.5.2  ff
+            roundtrip(false, "\xff");
+            // 3.5.3  fe fe ff ff
+            roundtrip(false, "\xfe\xfe\xff\xff");
+        }
+    }
+
+    SECTION("4  Overlong sequences")
+    {
+        // The following sequences are not malformed according to the letter of
+        // the Unicode 2.0 standard. However, they are longer then necessary and
+        // a correct UTF-8 encoder is not allowed to produce them. A "safe UTF-8
+        // decoder" should reject them just like malformed sequences for two
+        // reasons: (1) It helps to debug applications if overlong sequences are
+        // not treated as valid representations of characters, because this helps
+        // to spot problems more quickly. (2) Overlong sequences provide
+        // alternative representations of characters, that could maliciously be
+        // used to bypass filters that check only for ASCII characters. For
+        // instance, a 2-byte encoded line feed (LF) would not be caught by a
+        // line counter that counts only 0x0a bytes, but it would still be
+        // processed as a line feed by an unsafe UTF-8 decoder later in the
+        // pipeline. From a security point of view, ASCII compatibility of UTF-8
+        // sequences means also, that ASCII characters are *only* allowed to be
+        // represented by ASCII bytes in the range 0x00-0x7f. To ensure this
+        // aspect of ASCII compatibility, use only "safe UTF-8 decoders" that
+        // reject overlong UTF-8 sequences for which a shorter encoding exists.
+
+        SECTION("4.1  Examples of an overlong ASCII character")
+        {
+            // With a safe UTF-8 decoder, all the following five overlong
+            // representations of the ASCII character slash ("/") should be rejected
+            // like a malformed UTF-8 sequence, for instance by substituting it with
+            // a replacement character. If you see a slash below, you do not have a
+            // safe UTF-8 decoder!
+
+            // 4.1.1 U+002F = c0 af
+            roundtrip(false, "\xc0\xaf");
+            // 4.1.2 U+002F = e0 80 af
+            roundtrip(false, "\xe0\x80\xaf");
+            // 4.1.3 U+002F = f0 80 80 af
+            roundtrip(false, "\xf0\x80\x80\xaf");
+            // 4.1.4 U+002F = f8 80 80 80 af
+            roundtrip(false, "\xf8\x80\x80\x80\xaf");
+            // 4.1.5 U+002F = fc 80 80 80 80 af
+            roundtrip(false, "\xfc\x80\x80\x80\x80\xaf");
+        }
+
+        SECTION("4.2  Maximum overlong sequences")
+        {
+            // Below you see the highest Unicode value that is still resulting in an
+            // overlong sequence if represented with the given number of bytes. This
+            // is a boundary test for safe UTF-8 decoders. All five characters should
+            // be rejected like malformed UTF-8 sequences.
+
+            // 4.2.1  U-0000007F = c1 bf
+            roundtrip(false, "\xc1\xbf");
+            // 4.2.2  U-000007FF = e0 9f bf
+            roundtrip(false, "\xe0\x9f\xbf");
+            // 4.2.3  U-0000FFFF = f0 8f bf bf
+            roundtrip(false, "\xf0\x8f\xbf\xbf");
+            // 4.2.4  U-001FFFFF = f8 87 bf bf bf
+            roundtrip(false, "\xf8\x87\xbf\xbf\xbf");
+            // 4.2.5  U-03FFFFFF = fc 83 bf bf bf bf
+            roundtrip(false, "\xfc\x83\xbf\xbf\xbf\xbf");
+        }
+
+        SECTION("4.3  Overlong representation of the NUL character")
+        {
+            // The following five sequences should also be rejected like malformed
+            // UTF-8 sequences and should not be treated like the ASCII NUL
+            // character.
+
+            // 4.3.1  U+0000 = c0 80
+            roundtrip(false, "\xc0\x80");
+            // 4.3.2  U+0000 = e0 80 80
+            roundtrip(false, "\xe0\x80\x80");
+            // 4.3.3  U+0000 = f0 80 80 80
+            roundtrip(false, "\xf0\x80\x80\x80");
+            // 4.3.4  U+0000 = f8 80 80 80 80
+            roundtrip(false, "\xf8\x80\x80\x80\x80");
+            // 4.3.5  U+0000 = fc 80 80 80 80 80
+            roundtrip(false, "\xfc\x80\x80\x80\x80\x80");
+        }
+    }
+
+    SECTION("5  Illegal code positions")
+    {
+        // The following UTF-8 sequences should be rejected like malformed
+        // sequences, because they never represent valid ISO 10646 characters and
+        // a UTF-8 decoder that accepts them might introduce security problems
+        // comparable to overlong UTF-8 sequences.
+
+        SECTION("5.1 Single UTF-16 surrogates")
+        {
+            // 5.1.1  U+D800 = ed a0 80
+            roundtrip(false, "\xed\xa0\x80");
+            // 5.1.2  U+DB7F = ed ad bf
+            roundtrip(false, "\xed\xad\xbf");
+            // 5.1.3  U+DB80 = ed ae 80
+            roundtrip(false, "\xed\xae\x80");
+            // 5.1.4  U+DBFF = ed af bf
+            roundtrip(false, "\xed\xaf\xbf");
+            // 5.1.5  U+DC00 = ed b0 80
+            roundtrip(false, "\xed\xb0\x80");
+            // 5.1.6  U+DF80 = ed be 80
+            roundtrip(false, "\xed\xbe\x80");
+            // 5.1.7  U+DFFF = ed bf bf
+            roundtrip(false, "\xed\xbf\xbf");
+        }
+
+        SECTION("5.2 Paired UTF-16 surrogates")
+        {
+            // 5.2.1  U+D800 U+DC00 = ed a0 80 ed b0 80
+            roundtrip(false, "\xed\xa0\x80\xed\xb0\x80");
+            // 5.2.2  U+D800 U+DFFF = ed a0 80 ed bf bf
+            roundtrip(false, "\xed\xa0\x80\xed\xbf\xbf");
+            // 5.2.3  U+DB7F U+DC00 = ed ad bf ed b0 80
+            roundtrip(false, "\xed\xad\xbf\xed\xb0\x80");
+            // 5.2.4  U+DB7F U+DFFF = ed ad bf ed bf bf
+            roundtrip(false, "\xed\xad\xbf\xed\xbf\xbf");
+            // 5.2.5  U+DB80 U+DC00 = ed ae 80 ed b0 80
+            roundtrip(false, "\xed\xae\x80\xed\xb0\x80");
+            // 5.2.6  U+DB80 U+DFFF = ed ae 80 ed bf bf
+            roundtrip(false, "\xed\xae\x80\xed\xbf\xbf");
+            // 5.2.7  U+DBFF U+DC00 = ed af bf ed b0 80
+            roundtrip(false, "\xed\xaf\xbf\xed\xb0\x80");
+            // 5.2.8  U+DBFF U+DFFF = ed af bf ed bf bf
+            roundtrip(false, "\xed\xaf\xbf\xed\xbf\xbf");
+        }
+
+        SECTION("5.3 Noncharacter code positions")
+        {
+            // The following "noncharacters" are "reserved for internal use" by
+            // applications, and according to older versions of the Unicode Standard
+            // "should never be interchanged". Unicode Corrigendum #9 dropped the
+            // latter restriction. Nevertheless, their presence in incoming UTF-8 data
+            // can remain a potential security risk, depending on what use is made of
+            // these codes subsequently. Examples of such internal use:
+            //
+            //  - Some file APIs with 16-bit characters may use the integer value -1
+            //    = U+FFFF to signal an end-of-file (EOF) or error condition.
+            //
+            //  - In some UTF-16 receivers, code point U+FFFE might trigger a
+            //    byte-swap operation (to convert between UTF-16LE and UTF-16BE).
+            //
+            // With such internal use of noncharacters, it may be desirable and safer
+            // to block those code points in UTF-8 decoders, as they should never
+            // occur legitimately in incoming UTF-8 data, and could trigger unsafe
+            // behaviour in subsequent processing.
+
+            // Particularly problematic noncharacters in 16-bit applications:
+
+            // 5.3.1  U+FFFE = ef bf be
+            roundtrip(true, "\xef\xbf\xbe");
+            // 5.3.2  U+FFFF = ef bf bf
+            roundtrip(true, "\xef\xbf\xbf");
+
+            // 5.3.3  U+FDD0 .. U+FDEF
+            roundtrip(true, "\xEF\xB7\x90");
+            roundtrip(true, "\xEF\xB7\x91");
+            roundtrip(true, "\xEF\xB7\x92");
+            roundtrip(true, "\xEF\xB7\x93");
+            roundtrip(true, "\xEF\xB7\x94");
+            roundtrip(true, "\xEF\xB7\x95");
+            roundtrip(true, "\xEF\xB7\x96");
+            roundtrip(true, "\xEF\xB7\x97");
+            roundtrip(true, "\xEF\xB7\x98");
+            roundtrip(true, "\xEF\xB7\x99");
+            roundtrip(true, "\xEF\xB7\x9A");
+            roundtrip(true, "\xEF\xB7\x9B");
+            roundtrip(true, "\xEF\xB7\x9C");
+            roundtrip(true, "\xEF\xB7\x9D");
+            roundtrip(true, "\xEF\xB7\x9E");
+            roundtrip(true, "\xEF\xB7\x9F");
+            roundtrip(true, "\xEF\xB7\xA0");
+            roundtrip(true, "\xEF\xB7\xA1");
+            roundtrip(true, "\xEF\xB7\xA2");
+            roundtrip(true, "\xEF\xB7\xA3");
+            roundtrip(true, "\xEF\xB7\xA4");
+            roundtrip(true, "\xEF\xB7\xA5");
+            roundtrip(true, "\xEF\xB7\xA6");
+            roundtrip(true, "\xEF\xB7\xA7");
+            roundtrip(true, "\xEF\xB7\xA8");
+            roundtrip(true, "\xEF\xB7\xA9");
+            roundtrip(true, "\xEF\xB7\xAA");
+            roundtrip(true, "\xEF\xB7\xAB");
+            roundtrip(true, "\xEF\xB7\xAC");
+            roundtrip(true, "\xEF\xB7\xAD");
+            roundtrip(true, "\xEF\xB7\xAE");
+            roundtrip(true, "\xEF\xB7\xAF");
+
+            // 5.3.4  U+nFFFE U+nFFFF (for n = 1..10)
+            roundtrip(true, "\xF0\x9F\xBF\xBF");
+            roundtrip(true, "\xF0\xAF\xBF\xBF");
+            roundtrip(true, "\xF0\xBF\xBF\xBF");
+            roundtrip(true, "\xF1\x8F\xBF\xBF");
+            roundtrip(true, "\xF1\x9F\xBF\xBF");
+            roundtrip(true, "\xF1\xAF\xBF\xBF");
+            roundtrip(true, "\xF1\xBF\xBF\xBF");
+            roundtrip(true, "\xF2\x8F\xBF\xBF");
+            roundtrip(true, "\xF2\x9F\xBF\xBF");
+            roundtrip(true, "\xF2\xAF\xBF\xBF");
+        }
+    }
+}

tests/src/unit-unicode2.cpp

@@ -0,0 +1,612 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+// for some reason including this after the json header leads to linker errors with VS 2017...
+#include <locale>
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <fstream>
+#include <sstream>
+#include <iostream>
+#include <iomanip>
+#include "make_test_data_available.hpp"
+#include "test_utils.hpp"
+
+// this test suite uses static variables with non-trivial destructors
+DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
+DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
+
+namespace
+{
+extern size_t calls;
+size_t calls = 0;
+
+void check_utf8dump(bool success_expected, int byte1, int byte2, int byte3, int byte4);
+
+void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3 = -1, int byte4 = -1)
+{
+    static std::string json_string;
+    json_string.clear();
+
+    CAPTURE(byte1)
+    CAPTURE(byte2)
+    CAPTURE(byte3)
+    CAPTURE(byte4)
+
+    json_string += std::string(1, static_cast<char>(byte1));
+
+    if (byte2 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte2));
+    }
+
+    if (byte3 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte3));
+    }
+
+    if (byte4 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte4));
+    }
+
+    CAPTURE(json_string)
+
+    // store the string in a JSON value
+    static json j;
+    static json j2;
+    j = json_string;
+    j2 = "abc" + json_string + "xyz";
+
+    static std::string s_ignored;
+    static std::string s_ignored2;
+    static std::string s_ignored_ascii;
+    static std::string s_ignored2_ascii;
+    static std::string s_replaced;
+    static std::string s_replaced2;
+    static std::string s_replaced_ascii;
+    static std::string s_replaced2_ascii;
+
+    // dumping with ignore/replace must not throw in any case
+    s_ignored = j.dump(-1, ' ', false, json::error_handler_t::ignore);
+    s_ignored2 = j2.dump(-1, ' ', false, json::error_handler_t::ignore);
+    s_ignored_ascii = j.dump(-1, ' ', true, json::error_handler_t::ignore);
+    s_ignored2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::ignore);
+    s_replaced = j.dump(-1, ' ', false, json::error_handler_t::replace);
+    s_replaced2 = j2.dump(-1, ' ', false, json::error_handler_t::replace);
+    s_replaced_ascii = j.dump(-1, ' ', true, json::error_handler_t::replace);
+    s_replaced2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::replace);
+
+    if (success_expected)
+    {
+        static std::string s_strict;
+        // strict mode must not throw if success is expected
+        s_strict = j.dump();
+        // all dumps should agree on the string
+        CHECK(s_strict == s_ignored);
+        CHECK(s_strict == s_replaced);
+    }
+    else
+    {
+        // strict mode must throw if success is not expected
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
+        // ignore and replace must create different dumps
+        CHECK(s_ignored != s_replaced);
+
+        // check that replace string contains a replacement character
+        CHECK(s_replaced.find("\xEF\xBF\xBD") != std::string::npos);
+    }
+
+    // check that prefix and suffix are preserved
+    CHECK(s_ignored2.substr(1, 3) == "abc");
+    CHECK(s_ignored2.substr(s_ignored2.size() - 4, 3) == "xyz");
+    CHECK(s_ignored2_ascii.substr(1, 3) == "abc");
+    CHECK(s_ignored2_ascii.substr(s_ignored2_ascii.size() - 4, 3) == "xyz");
+    CHECK(s_replaced2.substr(1, 3) == "abc");
+    CHECK(s_replaced2.substr(s_replaced2.size() - 4, 3) == "xyz");
+    CHECK(s_replaced2_ascii.substr(1, 3) == "abc");
+    CHECK(s_replaced2_ascii.substr(s_replaced2_ascii.size() - 4, 3) == "xyz");
+}
+
+void check_utf8string(bool success_expected, int byte1, int byte2, int byte3, int byte4);
+
+// create and check a JSON string with up to four UTF-8 bytes
+void check_utf8string(bool success_expected, int byte1, int byte2 = -1, int byte3 = -1, int byte4 = -1)
+{
+    if (++calls % 100000 == 0)
+    {
+        std::cout << calls << " of 455355 UTF-8 strings checked" << std::endl; // NOLINT(performance-avoid-endl)
+    }
+
+    static std::string json_string;
+    json_string = "\"";
+
+    CAPTURE(byte1)
+    json_string += std::string(1, static_cast<char>(byte1));
+
+    if (byte2 != -1)
+    {
+        CAPTURE(byte2)
+        json_string += std::string(1, static_cast<char>(byte2));
+    }
+
+    if (byte3 != -1)
+    {
+        CAPTURE(byte3)
+        json_string += std::string(1, static_cast<char>(byte3));
+    }
+
+    if (byte4 != -1)
+    {
+        CAPTURE(byte4)
+        json_string += std::string(1, static_cast<char>(byte4));
+    }
+
+    json_string += "\"";
+
+    CAPTURE(json_string)
+
+    json _;
+    if (success_expected)
+    {
+        CHECK_NOTHROW(_ = json::parse(json_string));
+    }
+    else
+    {
+        CHECK_THROWS_AS(_ = json::parse(json_string), json::parse_error&);
+    }
+}
+} // namespace
+
+TEST_CASE("Unicode (2/5)" * doctest::skip())
+{
+    SECTION("RFC 3629")
+    {
+        /*
+        RFC 3629 describes in Sect. 4 the syntax of UTF-8 byte sequences as
+        follows:
+
+            A UTF-8 string is a sequence of octets representing a sequence of UCS
+            characters.  An octet sequence is valid UTF-8 only if it matches the
+            following syntax, which is derived from the rules for encoding UTF-8
+            and is expressed in the ABNF of [RFC2234].
+
+            UTF8-octets = *( UTF8-char )
+            UTF8-char   = UTF8-1 / UTF8-2 / UTF8-3 / UTF8-4
+            UTF8-1      = %x00-7F
+            UTF8-2      = %xC2-DF UTF8-tail
+            UTF8-3      = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /
+                          %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )
+            UTF8-4      = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /
+                          %xF4 %x80-8F 2( UTF8-tail )
+            UTF8-tail   = %x80-BF
+        */
+
+        SECTION("ill-formed first byte")
+        {
+            for (int byte1 = 0x80; byte1 <= 0xC1; ++byte1)
+            {
+                check_utf8string(false, byte1);
+                check_utf8dump(false, byte1);
+            }
+
+            for (int byte1 = 0xF5; byte1 <= 0xFF; ++byte1)
+            {
+                check_utf8string(false, byte1);
+                check_utf8dump(false, byte1);
+            }
+        }
+
+        SECTION("UTF8-1 (x00-x7F)")
+        {
+            SECTION("well-formed")
+            {
+                for (int byte1 = 0x00; byte1 <= 0x7F; ++byte1)
+                {
+                    // unescaped control characters are parse errors in JSON
+                    if (0x00 <= byte1 && byte1 <= 0x1F)
+                    {
+                        check_utf8string(false, byte1);
+                        continue;
+                    }
+
+                    // a single quote is a parse error in JSON
+                    if (byte1 == 0x22)
+                    {
+                        check_utf8string(false, byte1);
+                        continue;
+                    }
+
+                    // a single backslash is a parse error in JSON
+                    if (byte1 == 0x5C)
+                    {
+                        check_utf8string(false, byte1);
+                        continue;
+                    }
+
+                    // all other characters are OK
+                    check_utf8string(true, byte1);
+                    check_utf8dump(true, byte1);
+                }
+            }
+        }
+
+        SECTION("UTF8-2 (xC2-xDF UTF8-tail)")
+        {
+            SECTION("well-formed")
+            {
+                for (int byte1 = 0xC2; byte1 <= 0xDF; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        check_utf8string(true, byte1, byte2);
+                        check_utf8dump(true, byte1, byte2);
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing second byte")
+            {
+                for (int byte1 = 0xC2; byte1 <= 0xDF; ++byte1)
+                {
+                    check_utf8string(false, byte1);
+                    check_utf8dump(false, byte1);
+                }
+            }
+
+            SECTION("ill-formed: wrong second byte")
+            {
+                for (int byte1 = 0xC2; byte1 <= 0xDF; ++byte1)
+                {
+                    for (int byte2 = 0x00; byte2 <= 0xFF; ++byte2)
+                    {
+                        // skip correct second byte
+                        if (0x80 <= byte2 && byte2 <= 0xBF)
+                        {
+                            continue;
+                        }
+
+                        check_utf8string(false, byte1, byte2);
+                        check_utf8dump(false, byte1, byte2);
+                    }
+                }
+            }
+        }
+
+        SECTION("UTF8-3 (xE0 xA0-BF UTF8-tail)")
+        {
+            SECTION("well-formed")
+            {
+                for (int byte1 = 0xE0; byte1 <= 0xE0; ++byte1)
+                {
+                    for (int byte2 = 0xA0; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(true, byte1, byte2, byte3);
+                            check_utf8dump(true, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing second byte")
+            {
+                for (int byte1 = 0xE0; byte1 <= 0xE0; ++byte1)
+                {
+                    check_utf8string(false, byte1);
+                    check_utf8dump(false, byte1);
+                }
+            }
+
+            SECTION("ill-formed: missing third byte")
+            {
+                for (int byte1 = 0xE0; byte1 <= 0xE0; ++byte1)
+                {
+                    for (int byte2 = 0xA0; byte2 <= 0xBF; ++byte2)
+                    {
+                        check_utf8string(false, byte1, byte2);
+                        check_utf8dump(false, byte1, byte2);
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong second byte")
+            {
+                for (int byte1 = 0xE0; byte1 <= 0xE0; ++byte1)
+                {
+                    for (int byte2 = 0x00; byte2 <= 0xFF; ++byte2)
+                    {
+                        // skip correct second byte
+                        if (0xA0 <= byte2 && byte2 <= 0xBF)
+                        {
+                            continue;
+                        }
+
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong third byte")
+            {
+                for (int byte1 = 0xE0; byte1 <= 0xE0; ++byte1)
+                {
+                    for (int byte2 = 0xA0; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x00; byte3 <= 0xFF; ++byte3)
+                        {
+                            // skip correct third byte
+                            if (0x80 <= byte3 && byte3 <= 0xBF)
+                            {
+                                continue;
+                            }
+
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+        }
+
+        SECTION("UTF8-3 (xE1-xEC UTF8-tail UTF8-tail)")
+        {
+            SECTION("well-formed")
+            {
+                for (int byte1 = 0xE1; byte1 <= 0xEC; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(true, byte1, byte2, byte3);
+                            check_utf8dump(true, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing second byte")
+            {
+                for (int byte1 = 0xE1; byte1 <= 0xEC; ++byte1)
+                {
+                    check_utf8string(false, byte1);
+                    check_utf8dump(false, byte1);
+                }
+            }
+
+            SECTION("ill-formed: missing third byte")
+            {
+                for (int byte1 = 0xE1; byte1 <= 0xEC; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        check_utf8string(false, byte1, byte2);
+                        check_utf8dump(false, byte1, byte2);
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong second byte")
+            {
+                for (int byte1 = 0xE1; byte1 <= 0xEC; ++byte1)
+                {
+                    for (int byte2 = 0x00; byte2 <= 0xFF; ++byte2)
+                    {
+                        // skip correct second byte
+                        if (0x80 <= byte2 && byte2 <= 0xBF)
+                        {
+                            continue;
+                        }
+
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong third byte")
+            {
+                for (int byte1 = 0xE1; byte1 <= 0xEC; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x00; byte3 <= 0xFF; ++byte3)
+                        {
+                            // skip correct third byte
+                            if (0x80 <= byte3 && byte3 <= 0xBF)
+                            {
+                                continue;
+                            }
+
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+        }
+
+        SECTION("UTF8-3 (xED x80-9F UTF8-tail)")
+        {
+            SECTION("well-formed")
+            {
+                for (int byte1 = 0xED; byte1 <= 0xED; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0x9F; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(true, byte1, byte2, byte3);
+                            check_utf8dump(true, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing second byte")
+            {
+                for (int byte1 = 0xED; byte1 <= 0xED; ++byte1)
+                {
+                    check_utf8string(false, byte1);
+                    check_utf8dump(false, byte1);
+                }
+            }
+
+            SECTION("ill-formed: missing third byte")
+            {
+                for (int byte1 = 0xED; byte1 <= 0xED; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0x9F; ++byte2)
+                    {
+                        check_utf8string(false, byte1, byte2);
+                        check_utf8dump(false, byte1, byte2);
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong second byte")
+            {
+                for (int byte1 = 0xED; byte1 <= 0xED; ++byte1)
+                {
+                    for (int byte2 = 0x00; byte2 <= 0xFF; ++byte2)
+                    {
+                        // skip correct second byte
+                        if (0x80 <= byte2 && byte2 <= 0x9F)
+                        {
+                            continue;
+                        }
+
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong third byte")
+            {
+                for (int byte1 = 0xED; byte1 <= 0xED; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0x9F; ++byte2)
+                    {
+                        for (int byte3 = 0x00; byte3 <= 0xFF; ++byte3)
+                        {
+                            // skip correct third byte
+                            if (0x80 <= byte3 && byte3 <= 0xBF)
+                            {
+                                continue;
+                            }
+
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+        }
+
+        SECTION("UTF8-3 (xEE-xEF UTF8-tail UTF8-tail)")
+        {
+            SECTION("well-formed")
+            {
+                for (int byte1 = 0xEE; byte1 <= 0xEF; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(true, byte1, byte2, byte3);
+                            check_utf8dump(true, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing second byte")
+            {
+                for (int byte1 = 0xEE; byte1 <= 0xEF; ++byte1)
+                {
+                    check_utf8string(false, byte1);
+                    check_utf8dump(false, byte1);
+                }
+            }
+
+            SECTION("ill-formed: missing third byte")
+            {
+                for (int byte1 = 0xEE; byte1 <= 0xEF; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        check_utf8string(false, byte1, byte2);
+                        check_utf8dump(false, byte1, byte2);
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong second byte")
+            {
+                for (int byte1 = 0xEE; byte1 <= 0xEF; ++byte1)
+                {
+                    for (int byte2 = 0x00; byte2 <= 0xFF; ++byte2)
+                    {
+                        // skip correct second byte
+                        if (0x80 <= byte2 && byte2 <= 0xBF)
+                        {
+                            continue;
+                        }
+
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong third byte")
+            {
+                for (int byte1 = 0xEE; byte1 <= 0xEF; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x00; byte3 <= 0xFF; ++byte3)
+                        {
+                            // skip correct third byte
+                            if (0x80 <= byte3 && byte3 <= 0xBF)
+                            {
+                                continue;
+                            }
+
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+DOCTEST_CLANG_SUPPRESS_WARNING_POP

tests/src/unit-unicode3.cpp

@@ -0,0 +1,326 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+// for some reason including this after the json header leads to linker errors with VS 2017...
+#include <locale>
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <fstream>
+#include <sstream>
+#include <iostream>
+#include <iomanip>
+#include "make_test_data_available.hpp"
+#include "test_utils.hpp"
+
+// this test suite uses static variables with non-trivial destructors
+DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
+DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
+
+namespace
+{
+extern size_t calls;
+size_t calls = 0;
+
+void check_utf8dump(bool success_expected, int byte1, int byte2, int byte3, int byte4);
+
+void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3 = -1, int byte4 = -1)
+{
+    static std::string json_string;
+    json_string.clear();
+
+    CAPTURE(byte1)
+    CAPTURE(byte2)
+    CAPTURE(byte3)
+    CAPTURE(byte4)
+
+    json_string += std::string(1, static_cast<char>(byte1));
+
+    if (byte2 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte2));
+    }
+
+    if (byte3 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte3));
+    }
+
+    if (byte4 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte4));
+    }
+
+    CAPTURE(json_string)
+
+    // store the string in a JSON value
+    static json j;
+    static json j2;
+    j = json_string;
+    j2 = "abc" + json_string + "xyz";
+
+    static std::string s_ignored;
+    static std::string s_ignored2;
+    static std::string s_ignored_ascii;
+    static std::string s_ignored2_ascii;
+    static std::string s_replaced;
+    static std::string s_replaced2;
+    static std::string s_replaced_ascii;
+    static std::string s_replaced2_ascii;
+
+    // dumping with ignore/replace must not throw in any case
+    s_ignored = j.dump(-1, ' ', false, json::error_handler_t::ignore);
+    s_ignored2 = j2.dump(-1, ' ', false, json::error_handler_t::ignore);
+    s_ignored_ascii = j.dump(-1, ' ', true, json::error_handler_t::ignore);
+    s_ignored2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::ignore);
+    s_replaced = j.dump(-1, ' ', false, json::error_handler_t::replace);
+    s_replaced2 = j2.dump(-1, ' ', false, json::error_handler_t::replace);
+    s_replaced_ascii = j.dump(-1, ' ', true, json::error_handler_t::replace);
+    s_replaced2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::replace);
+
+    if (success_expected)
+    {
+        static std::string s_strict;
+        // strict mode must not throw if success is expected
+        s_strict = j.dump();
+        // all dumps should agree on the string
+        CHECK(s_strict == s_ignored);
+        CHECK(s_strict == s_replaced);
+    }
+    else
+    {
+        // strict mode must throw if success is not expected
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
+        // ignore and replace must create different dumps
+        CHECK(s_ignored != s_replaced);
+
+        // check that replace string contains a replacement character
+        CHECK(s_replaced.find("\xEF\xBF\xBD") != std::string::npos);
+    }
+
+    // check that prefix and suffix are preserved
+    CHECK(s_ignored2.substr(1, 3) == "abc");
+    CHECK(s_ignored2.substr(s_ignored2.size() - 4, 3) == "xyz");
+    CHECK(s_ignored2_ascii.substr(1, 3) == "abc");
+    CHECK(s_ignored2_ascii.substr(s_ignored2_ascii.size() - 4, 3) == "xyz");
+    CHECK(s_replaced2.substr(1, 3) == "abc");
+    CHECK(s_replaced2.substr(s_replaced2.size() - 4, 3) == "xyz");
+    CHECK(s_replaced2_ascii.substr(1, 3) == "abc");
+    CHECK(s_replaced2_ascii.substr(s_replaced2_ascii.size() - 4, 3) == "xyz");
+}
+
+void check_utf8string(bool success_expected, int byte1, int byte2, int byte3, int byte4);
+
+// create and check a JSON string with up to four UTF-8 bytes
+void check_utf8string(bool success_expected, int byte1, int byte2 = -1, int byte3 = -1, int byte4 = -1)
+{
+    if (++calls % 100000 == 0)
+    {
+        std::cout << calls << " of 1641521 UTF-8 strings checked" << std::endl; // NOLINT(performance-avoid-endl)
+    }
+
+    static std::string json_string;
+    json_string = "\"";
+
+    CAPTURE(byte1)
+    json_string += std::string(1, static_cast<char>(byte1));
+
+    if (byte2 != -1)
+    {
+        CAPTURE(byte2)
+        json_string += std::string(1, static_cast<char>(byte2));
+    }
+
+    if (byte3 != -1)
+    {
+        CAPTURE(byte3)
+        json_string += std::string(1, static_cast<char>(byte3));
+    }
+
+    if (byte4 != -1)
+    {
+        CAPTURE(byte4)
+        json_string += std::string(1, static_cast<char>(byte4));
+    }
+
+    json_string += "\"";
+
+    CAPTURE(json_string)
+
+    json _;
+    if (success_expected)
+    {
+        CHECK_NOTHROW(_ = json::parse(json_string));
+    }
+    else
+    {
+        CHECK_THROWS_AS(_ = json::parse(json_string), json::parse_error&);
+    }
+}
+} // namespace
+
+TEST_CASE("Unicode (3/5)" * doctest::skip())
+{
+    SECTION("RFC 3629")
+    {
+        /*
+        RFC 3629 describes in Sect. 4 the syntax of UTF-8 byte sequences as
+        follows:
+
+            A UTF-8 string is a sequence of octets representing a sequence of UCS
+            characters.  An octet sequence is valid UTF-8 only if it matches the
+            following syntax, which is derived from the rules for encoding UTF-8
+            and is expressed in the ABNF of [RFC2234].
+
+            UTF8-octets = *( UTF8-char )
+            UTF8-char   = UTF8-1 / UTF8-2 / UTF8-3 / UTF8-4
+            UTF8-1      = %x00-7F
+            UTF8-2      = %xC2-DF UTF8-tail
+            UTF8-3      = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /
+                          %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )
+            UTF8-4      = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /
+                          %xF4 %x80-8F 2( UTF8-tail )
+            UTF8-tail   = %x80-BF
+        */
+
+        SECTION("UTF8-4 (xF0 x90-BF UTF8-tail UTF8-tail)")
+        {
+            SECTION("well-formed")
+            {
+                for (int byte1 = 0xF0; byte1 <= 0xF0; ++byte1)
+                {
+                    for (int byte2 = 0x90; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            for (int byte4 = 0x80; byte4 <= 0xBF; ++byte4)
+                            {
+                                check_utf8string(true, byte1, byte2, byte3, byte4);
+                                check_utf8dump(true, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing second byte")
+            {
+                for (int byte1 = 0xF0; byte1 <= 0xF0; ++byte1)
+                {
+                    check_utf8string(false, byte1);
+                    check_utf8dump(false, byte1);
+                }
+            }
+
+            SECTION("ill-formed: missing third byte")
+            {
+                for (int byte1 = 0xF0; byte1 <= 0xF0; ++byte1)
+                {
+                    for (int byte2 = 0x90; byte2 <= 0xBF; ++byte2)
+                    {
+                        check_utf8string(false, byte1, byte2);
+                        check_utf8dump(false, byte1, byte2);
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing fourth byte")
+            {
+                for (int byte1 = 0xF0; byte1 <= 0xF0; ++byte1)
+                {
+                    for (int byte2 = 0x90; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong second byte")
+            {
+                for (int byte1 = 0xF0; byte1 <= 0xF0; ++byte1)
+                {
+                    for (int byte2 = 0x00; byte2 <= 0xFF; ++byte2)
+                    {
+                        // skip correct second byte
+                        if (0x90 <= byte2 && byte2 <= 0xBF)
+                        {
+                            continue;
+                        }
+
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            for (int byte4 = 0x80; byte4 <= 0xBF; ++byte4)
+                            {
+                                check_utf8string(false, byte1, byte2, byte3, byte4);
+                                check_utf8dump(false, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong third byte")
+            {
+                for (int byte1 = 0xF0; byte1 <= 0xF0; ++byte1)
+                {
+                    for (int byte2 = 0x90; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x00; byte3 <= 0xFF; ++byte3)
+                        {
+                            // skip correct third byte
+                            if (0x80 <= byte3 && byte3 <= 0xBF)
+                            {
+                                continue;
+                            }
+
+                            for (int byte4 = 0x80; byte4 <= 0xBF; ++byte4)
+                            {
+                                check_utf8string(false, byte1, byte2, byte3, byte4);
+                                check_utf8dump(false, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong fourth byte")
+            {
+                for (int byte1 = 0xF0; byte1 <= 0xF0; ++byte1)
+                {
+                    for (int byte2 = 0x90; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            for (int byte4 = 0x00; byte4 <= 0xFF; ++byte4)
+                            {
+                                // skip correct fourth byte
+                                if (0x80 <= byte4 && byte4 <= 0xBF)
+                                {
+                                    continue;
+                                }
+
+                                check_utf8string(false, byte1, byte2, byte3, byte4);
+                                check_utf8dump(false, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+DOCTEST_CLANG_SUPPRESS_WARNING_POP

tests/src/unit-unicode4.cpp

@@ -0,0 +1,326 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+// for some reason including this after the json header leads to linker errors with VS 2017...
+#include <locale>
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <fstream>
+#include <sstream>
+#include <iostream>
+#include <iomanip>
+#include "make_test_data_available.hpp"
+#include "test_utils.hpp"
+
+// this test suite uses static variables with non-trivial destructors
+DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
+DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
+
+namespace
+{
+extern size_t calls;
+size_t calls = 0;
+
+void check_utf8dump(bool success_expected, int byte1, int byte2, int byte3, int byte4);
+
+void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3 = -1, int byte4 = -1)
+{
+    static std::string json_string;
+    json_string.clear();
+
+    CAPTURE(byte1)
+    CAPTURE(byte2)
+    CAPTURE(byte3)
+    CAPTURE(byte4)
+
+    json_string += std::string(1, static_cast<char>(byte1));
+
+    if (byte2 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte2));
+    }
+
+    if (byte3 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte3));
+    }
+
+    if (byte4 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte4));
+    }
+
+    CAPTURE(json_string)
+
+    // store the string in a JSON value
+    static json j;
+    static json j2;
+    j = json_string;
+    j2 = "abc" + json_string + "xyz";
+
+    static std::string s_ignored;
+    static std::string s_ignored2;
+    static std::string s_ignored_ascii;
+    static std::string s_ignored2_ascii;
+    static std::string s_replaced;
+    static std::string s_replaced2;
+    static std::string s_replaced_ascii;
+    static std::string s_replaced2_ascii;
+
+    // dumping with ignore/replace must not throw in any case
+    s_ignored = j.dump(-1, ' ', false, json::error_handler_t::ignore);
+    s_ignored2 = j2.dump(-1, ' ', false, json::error_handler_t::ignore);
+    s_ignored_ascii = j.dump(-1, ' ', true, json::error_handler_t::ignore);
+    s_ignored2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::ignore);
+    s_replaced = j.dump(-1, ' ', false, json::error_handler_t::replace);
+    s_replaced2 = j2.dump(-1, ' ', false, json::error_handler_t::replace);
+    s_replaced_ascii = j.dump(-1, ' ', true, json::error_handler_t::replace);
+    s_replaced2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::replace);
+
+    if (success_expected)
+    {
+        static std::string s_strict;
+        // strict mode must not throw if success is expected
+        s_strict = j.dump();
+        // all dumps should agree on the string
+        CHECK(s_strict == s_ignored);
+        CHECK(s_strict == s_replaced);
+    }
+    else
+    {
+        // strict mode must throw if success is not expected
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
+        // ignore and replace must create different dumps
+        CHECK(s_ignored != s_replaced);
+
+        // check that replace string contains a replacement character
+        CHECK(s_replaced.find("\xEF\xBF\xBD") != std::string::npos);
+    }
+
+    // check that prefix and suffix are preserved
+    CHECK(s_ignored2.substr(1, 3) == "abc");
+    CHECK(s_ignored2.substr(s_ignored2.size() - 4, 3) == "xyz");
+    CHECK(s_ignored2_ascii.substr(1, 3) == "abc");
+    CHECK(s_ignored2_ascii.substr(s_ignored2_ascii.size() - 4, 3) == "xyz");
+    CHECK(s_replaced2.substr(1, 3) == "abc");
+    CHECK(s_replaced2.substr(s_replaced2.size() - 4, 3) == "xyz");
+    CHECK(s_replaced2_ascii.substr(1, 3) == "abc");
+    CHECK(s_replaced2_ascii.substr(s_replaced2_ascii.size() - 4, 3) == "xyz");
+}
+
+void check_utf8string(bool success_expected, int byte1, int byte2, int byte3, int byte4);
+
+// create and check a JSON string with up to four UTF-8 bytes
+void check_utf8string(bool success_expected, int byte1, int byte2 = -1, int byte3 = -1, int byte4 = -1)
+{
+    if (++calls % 100000 == 0)
+    {
+        std::cout << calls << " of 5517507 UTF-8 strings checked" << std::endl; // NOLINT(performance-avoid-endl)
+    }
+
+    static std::string json_string;
+    json_string = "\"";
+
+    CAPTURE(byte1)
+    json_string += std::string(1, static_cast<char>(byte1));
+
+    if (byte2 != -1)
+    {
+        CAPTURE(byte2)
+        json_string += std::string(1, static_cast<char>(byte2));
+    }
+
+    if (byte3 != -1)
+    {
+        CAPTURE(byte3)
+        json_string += std::string(1, static_cast<char>(byte3));
+    }
+
+    if (byte4 != -1)
+    {
+        CAPTURE(byte4)
+        json_string += std::string(1, static_cast<char>(byte4));
+    }
+
+    json_string += "\"";
+
+    CAPTURE(json_string)
+
+    json _;
+    if (success_expected)
+    {
+        CHECK_NOTHROW(_ = json::parse(json_string));
+    }
+    else
+    {
+        CHECK_THROWS_AS(_ = json::parse(json_string), json::parse_error&);
+    }
+}
+} // namespace
+
+TEST_CASE("Unicode (4/5)" * doctest::skip())
+{
+    SECTION("RFC 3629")
+    {
+        /*
+        RFC 3629 describes in Sect. 4 the syntax of UTF-8 byte sequences as
+        follows:
+
+            A UTF-8 string is a sequence of octets representing a sequence of UCS
+            characters.  An octet sequence is valid UTF-8 only if it matches the
+            following syntax, which is derived from the rules for encoding UTF-8
+            and is expressed in the ABNF of [RFC2234].
+
+            UTF8-octets = *( UTF8-char )
+            UTF8-char   = UTF8-1 / UTF8-2 / UTF8-3 / UTF8-4
+            UTF8-1      = %x00-7F
+            UTF8-2      = %xC2-DF UTF8-tail
+            UTF8-3      = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /
+                          %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )
+            UTF8-4      = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /
+                          %xF4 %x80-8F 2( UTF8-tail )
+            UTF8-tail   = %x80-BF
+        */
+
+        SECTION("UTF8-4 (xF1-F3 UTF8-tail UTF8-tail UTF8-tail)")
+        {
+            SECTION("well-formed")
+            {
+                for (int byte1 = 0xF1; byte1 <= 0xF3; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            for (int byte4 = 0x80; byte4 <= 0xBF; ++byte4)
+                            {
+                                check_utf8string(true, byte1, byte2, byte3, byte4);
+                                check_utf8dump(true, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing second byte")
+            {
+                for (int byte1 = 0xF1; byte1 <= 0xF3; ++byte1)
+                {
+                    check_utf8string(false, byte1);
+                    check_utf8dump(false, byte1);
+                }
+            }
+
+            SECTION("ill-formed: missing third byte")
+            {
+                for (int byte1 = 0xF1; byte1 <= 0xF3; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        check_utf8string(false, byte1, byte2);
+                        check_utf8dump(false, byte1, byte2);
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing fourth byte")
+            {
+                for (int byte1 = 0xF1; byte1 <= 0xF3; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong second byte")
+            {
+                for (int byte1 = 0xF1; byte1 <= 0xF3; ++byte1)
+                {
+                    for (int byte2 = 0x00; byte2 <= 0xFF; ++byte2)
+                    {
+                        // skip correct second byte
+                        if (0x80 <= byte2 && byte2 <= 0xBF)
+                        {
+                            continue;
+                        }
+
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            for (int byte4 = 0x80; byte4 <= 0xBF; ++byte4)
+                            {
+                                check_utf8string(false, byte1, byte2, byte3, byte4);
+                                check_utf8dump(false, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong third byte")
+            {
+                for (int byte1 = 0xF1; byte1 <= 0xF3; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x00; byte3 <= 0xFF; ++byte3)
+                        {
+                            // skip correct third byte
+                            if (0x80 <= byte3 && byte3 <= 0xBF)
+                            {
+                                continue;
+                            }
+
+                            for (int byte4 = 0x80; byte4 <= 0xBF; ++byte4)
+                            {
+                                check_utf8string(false, byte1, byte2, byte3, byte4);
+                                check_utf8dump(false, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong fourth byte")
+            {
+                for (int byte1 = 0xF1; byte1 <= 0xF3; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0xBF; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            for (int byte4 = 0x00; byte4 <= 0xFF; ++byte4)
+                            {
+                                // skip correct fourth byte
+                                if (0x80 <= byte4 && byte4 <= 0xBF)
+                                {
+                                    continue;
+                                }
+
+                                check_utf8string(false, byte1, byte2, byte3, byte4);
+                                check_utf8dump(false, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+DOCTEST_CLANG_SUPPRESS_WARNING_POP

tests/src/unit-unicode5.cpp

@@ -0,0 +1,326 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+// for some reason including this after the json header leads to linker errors with VS 2017...
+#include <locale>
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <fstream>
+#include <sstream>
+#include <iostream>
+#include <iomanip>
+#include "make_test_data_available.hpp"
+#include "test_utils.hpp"
+
+// this test suite uses static variables with non-trivial destructors
+DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
+DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
+
+namespace
+{
+extern size_t calls;
+size_t calls = 0;
+
+void check_utf8dump(bool success_expected, int byte1, int byte2, int byte3, int byte4);
+
+void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3 = -1, int byte4 = -1)
+{
+    static std::string json_string;
+    json_string.clear();
+
+    CAPTURE(byte1)
+    CAPTURE(byte2)
+    CAPTURE(byte3)
+    CAPTURE(byte4)
+
+    json_string += std::string(1, static_cast<char>(byte1));
+
+    if (byte2 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte2));
+    }
+
+    if (byte3 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte3));
+    }
+
+    if (byte4 != -1)
+    {
+        json_string += std::string(1, static_cast<char>(byte4));
+    }
+
+    CAPTURE(json_string)
+
+    // store the string in a JSON value
+    static json j;
+    static json j2;
+    j = json_string;
+    j2 = "abc" + json_string + "xyz";
+
+    static std::string s_ignored;
+    static std::string s_ignored2;
+    static std::string s_ignored_ascii;
+    static std::string s_ignored2_ascii;
+    static std::string s_replaced;
+    static std::string s_replaced2;
+    static std::string s_replaced_ascii;
+    static std::string s_replaced2_ascii;
+
+    // dumping with ignore/replace must not throw in any case
+    s_ignored = j.dump(-1, ' ', false, json::error_handler_t::ignore);
+    s_ignored2 = j2.dump(-1, ' ', false, json::error_handler_t::ignore);
+    s_ignored_ascii = j.dump(-1, ' ', true, json::error_handler_t::ignore);
+    s_ignored2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::ignore);
+    s_replaced = j.dump(-1, ' ', false, json::error_handler_t::replace);
+    s_replaced2 = j2.dump(-1, ' ', false, json::error_handler_t::replace);
+    s_replaced_ascii = j.dump(-1, ' ', true, json::error_handler_t::replace);
+    s_replaced2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::replace);
+
+    if (success_expected)
+    {
+        static std::string s_strict;
+        // strict mode must not throw if success is expected
+        s_strict = j.dump();
+        // all dumps should agree on the string
+        CHECK(s_strict == s_ignored);
+        CHECK(s_strict == s_replaced);
+    }
+    else
+    {
+        // strict mode must throw if success is not expected
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
+        // ignore and replace must create different dumps
+        CHECK(s_ignored != s_replaced);
+
+        // check that replace string contains a replacement character
+        CHECK(s_replaced.find("\xEF\xBF\xBD") != std::string::npos);
+    }
+
+    // check that prefix and suffix are preserved
+    CHECK(s_ignored2.substr(1, 3) == "abc");
+    CHECK(s_ignored2.substr(s_ignored2.size() - 4, 3) == "xyz");
+    CHECK(s_ignored2_ascii.substr(1, 3) == "abc");
+    CHECK(s_ignored2_ascii.substr(s_ignored2_ascii.size() - 4, 3) == "xyz");
+    CHECK(s_replaced2.substr(1, 3) == "abc");
+    CHECK(s_replaced2.substr(s_replaced2.size() - 4, 3) == "xyz");
+    CHECK(s_replaced2_ascii.substr(1, 3) == "abc");
+    CHECK(s_replaced2_ascii.substr(s_replaced2_ascii.size() - 4, 3) == "xyz");
+}
+
+void check_utf8string(bool success_expected, int byte1, int byte2, int byte3, int byte4);
+
+// create and check a JSON string with up to four UTF-8 bytes
+void check_utf8string(bool success_expected, int byte1, int byte2 = -1, int byte3 = -1, int byte4 = -1)
+{
+    if (++calls % 100000 == 0)
+    {
+        std::cout << calls << " of 1246225 UTF-8 strings checked" << std::endl; // NOLINT(performance-avoid-endl)
+    }
+
+    static std::string json_string;
+    json_string = "\"";
+
+    CAPTURE(byte1)
+    json_string += std::string(1, static_cast<char>(byte1));
+
+    if (byte2 != -1)
+    {
+        CAPTURE(byte2)
+        json_string += std::string(1, static_cast<char>(byte2));
+    }
+
+    if (byte3 != -1)
+    {
+        CAPTURE(byte3)
+        json_string += std::string(1, static_cast<char>(byte3));
+    }
+
+    if (byte4 != -1)
+    {
+        CAPTURE(byte4)
+        json_string += std::string(1, static_cast<char>(byte4));
+    }
+
+    json_string += "\"";
+
+    CAPTURE(json_string)
+
+    json _;
+    if (success_expected)
+    {
+        CHECK_NOTHROW(_ = json::parse(json_string));
+    }
+    else
+    {
+        CHECK_THROWS_AS(_ = json::parse(json_string), json::parse_error&);
+    }
+}
+} // namespace
+
+TEST_CASE("Unicode (5/5)" * doctest::skip())
+{
+    SECTION("RFC 3629")
+    {
+        /*
+        RFC 3629 describes in Sect. 4 the syntax of UTF-8 byte sequences as
+        follows:
+
+            A UTF-8 string is a sequence of octets representing a sequence of UCS
+            characters.  An octet sequence is valid UTF-8 only if it matches the
+            following syntax, which is derived from the rules for encoding UTF-8
+            and is expressed in the ABNF of [RFC2234].
+
+            UTF8-octets = *( UTF8-char )
+            UTF8-char   = UTF8-1 / UTF8-2 / UTF8-3 / UTF8-4
+            UTF8-1      = %x00-7F
+            UTF8-2      = %xC2-DF UTF8-tail
+            UTF8-3      = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /
+                          %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )
+            UTF8-4      = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /
+                          %xF4 %x80-8F 2( UTF8-tail )
+            UTF8-tail   = %x80-BF
+        */
+
+        SECTION("UTF8-4 (xF4 x80-8F UTF8-tail UTF8-tail)")
+        {
+            SECTION("well-formed")
+            {
+                for (int byte1 = 0xF4; byte1 <= 0xF4; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0x8F; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            for (int byte4 = 0x80; byte4 <= 0xBF; ++byte4)
+                            {
+                                check_utf8string(true, byte1, byte2, byte3, byte4);
+                                check_utf8dump(true, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing second byte")
+            {
+                for (int byte1 = 0xF4; byte1 <= 0xF4; ++byte1)
+                {
+                    check_utf8string(false, byte1);
+                    check_utf8dump(false, byte1);
+                }
+            }
+
+            SECTION("ill-formed: missing third byte")
+            {
+                for (int byte1 = 0xF4; byte1 <= 0xF4; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0x8F; ++byte2)
+                    {
+                        check_utf8string(false, byte1, byte2);
+                        check_utf8dump(false, byte1, byte2);
+                    }
+                }
+            }
+
+            SECTION("ill-formed: missing fourth byte")
+            {
+                for (int byte1 = 0xF4; byte1 <= 0xF4; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0x8F; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            check_utf8string(false, byte1, byte2, byte3);
+                            check_utf8dump(false, byte1, byte2, byte3);
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong second byte")
+            {
+                for (int byte1 = 0xF4; byte1 <= 0xF4; ++byte1)
+                {
+                    for (int byte2 = 0x00; byte2 <= 0xFF; ++byte2)
+                    {
+                        // skip correct second byte
+                        if (0x80 <= byte2 && byte2 <= 0x8F)
+                        {
+                            continue;
+                        }
+
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            for (int byte4 = 0x80; byte4 <= 0xBF; ++byte4)
+                            {
+                                check_utf8string(false, byte1, byte2, byte3, byte4);
+                                check_utf8dump(false, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong third byte")
+            {
+                for (int byte1 = 0xF4; byte1 <= 0xF4; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0x8F; ++byte2)
+                    {
+                        for (int byte3 = 0x00; byte3 <= 0xFF; ++byte3)
+                        {
+                            // skip correct third byte
+                            if (0x80 <= byte3 && byte3 <= 0xBF)
+                            {
+                                continue;
+                            }
+
+                            for (int byte4 = 0x80; byte4 <= 0xBF; ++byte4)
+                            {
+                                check_utf8string(false, byte1, byte2, byte3, byte4);
+                                check_utf8dump(false, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+
+            SECTION("ill-formed: wrong fourth byte")
+            {
+                for (int byte1 = 0xF4; byte1 <= 0xF4; ++byte1)
+                {
+                    for (int byte2 = 0x80; byte2 <= 0x8F; ++byte2)
+                    {
+                        for (int byte3 = 0x80; byte3 <= 0xBF; ++byte3)
+                        {
+                            for (int byte4 = 0x00; byte4 <= 0xFF; ++byte4)
+                            {
+                                // skip correct fourth byte
+                                if (0x80 <= byte4 && byte4 <= 0xBF)
+                                {
+                                    continue;
+                                }
+
+                                check_utf8string(false, byte1, byte2, byte3, byte4);
+                                check_utf8dump(false, byte1, byte2, byte3, byte4);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+DOCTEST_CLANG_SUPPRESS_WARNING_POP