Overwork project infrastructure (#5218)

* 📝 overwork project infrastructure

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

* 🐛 fix GCC16 issue

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

* 🐛 fix GCC16 issue

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

* 🐛 only build module for GCC

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

* 🐛 fix build

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

* 📝 fix documentation

Closes #5012: fix the error_handler_t::ignore wording

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

* 📝 fix documentation

Closes #4354: fix "Custom data source" example

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

---------

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

.cirrus.yml

@@ -3,15 +3,15 @@ arm_container:
 
 check_task:
   check_script:
-  - wget https://github.com/Kitware/CMake/releases/download/v3.20.2/cmake-3.20.2.tar.gz
+  # the gcc image ships an outdated CMake, so fetch a recent prebuilt binary
-  - tar xfz cmake-3.20.2.tar.gz
+  # instead of compiling CMake from source
-  - cd cmake-3.20.2
+  - wget -q https://github.com/Kitware/CMake/releases/download/v4.3.4/cmake-4.3.4-linux-aarch64.tar.gz
-  - ./configure
+  - tar xfz cmake-4.3.4-linux-aarch64.tar.gz
-  - make cmake ctest -j4
+  - export PATH="$(pwd)/cmake-4.3.4-linux-aarch64/bin:$PATH"
-  - cd ..
+  - cmake --version
   - mkdir build
   - cd build
-  - ../cmake-3.20.2/bin/cmake .. -DJSON_FastTests=ON
+  - cmake .. -DJSON_FastTests=ON
   - make -j4
   - cd tests
-  - ../../cmake-3.20.2/bin/ctest -j4
+  - ctest -j4

.github/config.yml

@@ -13,7 +13,7 @@ sentimentBotReplyComment: >
 
 # *Required* Comment to reply with
 requestInfoReplyComment: >
-  We would appreciate it if you could provide us with more info about this issue or pull request! Please check the [issue template](https://github.com/nlohmann/json/blob/develop/.github/ISSUE_TEMPLATE.md) and the [pull request template](https://github.com/nlohmann/json/blob/develop/.github/PULL_REQUEST_TEMPLATE.md).
+  We would appreciate it if you could provide us with more info about this issue or pull request! Please check the [issue template](https://github.com/nlohmann/json/issues/new/choose) and the [pull request template](https://github.com/nlohmann/json/blob/develop/.github/PULL_REQUEST_TEMPLATE.md).
 
 # *OPTIONAL* Label to be added to Issues and Pull Requests with insufficient information given
 requestInfoLabelToAdd: "state: needs more info"

.github/labeler.yml

@@ -23,11 +23,11 @@ labels:
 
 - label: "CI"
   files:
-    - "github/workflows/.*"
+    - ".github/workflows/.*"
 
 - label: "CI"
   files:
-    - "github/external_ci/.*"
+    - ".github/external_ci/.*"
 
 - label: "S"
   size-below: 10

.github/workflows/check_amalgamation.yml

@@ -43,12 +43,14 @@ jobs:
         with:
           path: main
           ref: ${{ github.event.pull_request.head.sha }}
+          persist-credentials: false
 
       - name: Checkout tools
         uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           path: tools
           ref: develop
+          persist-credentials: false
 
       - name: Install astyle
         run: |

.github/workflows/cifuzz.yml

@@ -13,6 +13,9 @@ jobs:
       with:
         egress-policy: audit
 
+    # The OSS-Fuzz CIFuzz actions are referenced via @master as recommended by
+    # the OSS-Fuzz documentation; the project does not publish tags or releases
+    # to pin to. See https://google.github.io/oss-fuzz/getting-started/continuous-integration/
     - name: Build Fuzzers
       id: build
       uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@master

.github/workflows/codeql-analysis.yml

@@ -33,6 +33,8 @@ jobs:
 
     - name: Checkout repository
       uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+      with:
+        persist-credentials: false
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL

.github/workflows/dependency-review.yml

@@ -23,5 +23,7 @@ jobs:
 
       - name: 'Checkout Repository'
         uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: 'Dependency Review'
         uses: actions/dependency-review-action@a1d282b36b6f3519aa1f3fc636f609c47dddb294 # v5.0.0

.github/workflows/flawfinder.yml

@@ -33,6 +33,8 @@ jobs:
 
       - name: Checkout code
         uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
 
       - name: flawfinder_scan
         uses: david-a-wheeler/flawfinder@c4216b74cf2639ffa98503768bd6e4299b5440c9 # v2.0.20
@@ -41,6 +43,6 @@ jobs:
           output: 'flawfinder_results.sarif'
 
       - name: Upload analysis results to GitHub Security tab
-        uses: github/codeql-action/upload-sarif@8aad20d150bbac5944a9f9d289da16a4b0d87c1e # v4
+        uses: github/codeql-action/upload-sarif@8aad20d150bbac5944a9f9d289da16a4b0d87c1e # v4.36.2
         with:
           sarif_file: ${{github.workspace}}/flawfinder_results.sarif

.github/workflows/labeler.yml

@@ -21,6 +21,6 @@ jobs:
         with:
           egress-policy: audit
 
-      - uses: srvaroa/labeler@e8fbb2561481ef6e711a770f0234e9379dc76892 # master
+      - uses: srvaroa/labeler@bf262763a8a8e191f5847873aecc0f29df84f957 # v1.14.0
         env:
           GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"

.github/workflows/macos.yml

@@ -17,60 +17,6 @@ permissions:
   contents: read
 
 jobs:
-# macos-11 is deprecated
-#  macos-11:
-#    runs-on: macos-11
-#    strategy:
-#      matrix:
-#        xcode: ['11.7', '12.4', '12.5.1', '13.0']
-#    env:
-#      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
-#
-#    steps:
-#      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
-#      - name: Run CMake
-#        run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_FastTests=ON
-#      - name: Build
-#        run: cmake --build build --parallel 10
-#      - name: Test
-#        run: cd build ; ctest -j 10 --output-on-failure
-
-# macos-12 is deprecated (https://github.com/actions/runner-images/issues/10721)
-#  macos-12:
-#    runs-on: macos-12 # https://github.com/actions/runner-images/blob/main/images/macos/macos-12-Readme.md
-#    strategy:
-#      matrix:
-#        xcode: ['13.1', '13.2.1', '13.3.1', '13.4.1', '14.0', '14.0.1', '14.1']
-#    env:
-#      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
-#
-#    steps:
-#      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
-#      - name: Run CMake
-#        run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_FastTests=ON
-#      - name: Build
-#        run: cmake --build build --parallel 10
-#      - name: Test
-#        run: cd build ; ctest -j 10 --output-on-failure
-
-# macos-13 is deprecated (https://github.com/actions/runner-images/issues/13046)
-#  macos-13:
-#    runs-on: macos-13 # https://github.com/actions/runner-images/blob/main/images/macos/macos-13-Readme.md
-#    strategy:
-#      matrix:
-#        xcode: ['14.1', '14.2', '14.3', '14.3.1', '15.0.1', '15.1', '15.2']
-#    env:
-#      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
-#
-#    steps:
-#      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
-#      - name: Run CMake
-#        run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_FastTests=ON
-#      - name: Build
-#        run: cmake --build build --parallel 10
-#      - name: Test
-#        run: cd build ; ctest -j 10 --output-on-failure
-
   macos-14:
     runs-on: macos-14 # https://github.com/actions/runner-images/blob/main/images/macos/macos-14-Readme.md
     strategy:
@@ -81,6 +27,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Run CMake
         run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_FastTests=ON
       - name: Build
@@ -98,6 +46,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Run CMake
         run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_FastTests=ON
       - name: Build
@@ -113,6 +63,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Run CMake
         run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_TestStandards=${{ matrix.standard }}
       - name: Build

.github/workflows/semgrep.yml

@@ -38,6 +38,8 @@ jobs:
 
       # Checkout project source
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
 
       # Scan code using project's configuration on https://semgrep.dev/manage
       - uses: returntocorp/semgrep-action@713efdd345f3035192eaa63f56867b88e63e4e5d
@@ -48,7 +50,7 @@ jobs:
 
       # Upload SARIF file generated in previous step
       - name: Upload SARIF file
-        uses: github/codeql-action/upload-sarif@8aad20d150bbac5944a9f9d289da16a4b0d87c1e # v4
+        uses: github/codeql-action/upload-sarif@8aad20d150bbac5944a9f9d289da16a4b0d87c1e # v4.36.2
         with:
           sarif_file: semgrep.sarif
         if: always()

.github/workflows/ubuntu.yml

@@ -22,6 +22,8 @@ jobs:
     container: gcc:latest
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
@@ -34,6 +36,8 @@ jobs:
     container: ghcr.io/nlohmann/json-ci:v2.4.0
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -53,6 +57,8 @@ jobs:
       - name: Install Valgrind
         run: sudo apt-get update ; sudo apt-get install -y valgrind
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
@@ -70,6 +76,8 @@ jobs:
       - name: Install git, clang-tools, iwyu (ci_single_binaries), and unzip
         run: apt-get update ; apt-get install -y git clang-tools iwyu unzip
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
@@ -87,6 +95,8 @@ jobs:
       - name: Install build-essential
         run: apt-get update ; apt-get install -y build-essential unzip wget git libssl-dev
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
@@ -103,6 +113,8 @@ jobs:
           egress-policy: audit
 
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Install dependencies and de_DE locale
         run: |
           sudo apt-get clean
@@ -134,6 +146,8 @@ jobs:
     container: ghcr.io/nlohmann/json-ci:v2.4.0
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Run CMake
         run: CXX=g++-${{ matrix.compiler }} cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -148,6 +162,8 @@ jobs:
     container: gcc:${{ matrix.compiler }}
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
@@ -163,6 +179,8 @@ jobs:
     container: silkeh/clang:${{ matrix.compiler }}
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Set env FORCE_STDCPPFS_FLAG for clang 7 / 8 / 9 / 10
@@ -181,6 +199,8 @@ jobs:
         standard: [11, 14, 17, 20, 23, 26]
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
@@ -199,6 +219,8 @@ jobs:
       - name: Install git and unzip
         run: apt-get update ; apt-get install -y git unzip
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
@@ -215,6 +237,8 @@ jobs:
     container: ghcr.io/nlohmann/json-ci:v2.4.0
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -228,8 +252,23 @@ jobs:
     container: ${{ matrix.container }}
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
-      - name: Get latest CMake and ninja
+        with:
+          persist-credentials: false
+      # The module test uses `import std;`, which needs CMake's experimental
+      # import-std support. Its opt-in token is CMake-version-specific, so pin
+      # CMake to the version whose token is set in tests/module_cpp20/CMakeLists.txt.
+      - name: Get pinned CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
+        with:
+          cmakeVersion: 4.3.4
+      # Clang: the std library module is provided by libc++ (the image's libstdc++
+      # ships none), and the image's libc++ module manifest has a broken relative
+      # path — repoint it at the real module sources.
+      - name: Use libc++ and fix its module manifest path (Clang)
+        if: matrix.container == 'silkeh/clang:latest'
+        run: |
+          echo "CXXFLAGS=-stdlib=libc++" >> "$GITHUB_ENV"
+          mkdir -p /usr/lib/share && ln -sf /usr/lib/llvm-*/share/libc++ /usr/lib/share/libc++
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -240,6 +279,8 @@ jobs:
     container: ghcr.io/nlohmann/json-ci:v2.2.0
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -258,6 +299,8 @@ jobs:
       - name: Install emscripten
         uses: mymindstorm/setup-emsdk@4528d102f7230f0e7b276855c01ea1159be0e984 # v16
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
@@ -277,6 +320,8 @@ jobs:
           egress-policy: audit
 
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build

.github/workflows/windows.yml

@@ -25,6 +25,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Set up MinGW
         uses: egor-tensin/setup-mingw@41b837e47d7f85214629d255b9c4bc3fcbe9fd63 # v3.0
         with:
@@ -48,6 +50,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Set extra CXX_FLAGS for latest std_version
         id: cxxflags
         run: |
@@ -78,6 +82,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Install Clang
         run: curl -fsSL -o LLVM${{ matrix.version }}.exe https://github.com/llvm/llvm-project/releases/download/llvmorg-${{ matrix.version }}/LLVM-${{ matrix.version }}-win64.exe ; 7z x LLVM${{ matrix.version }}.exe -y -o"C:/Program Files/LLVM"
       - name: Set up MinGW
@@ -106,6 +112,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
       - name: Run CMake
         run: cmake -S . -B build -G "Visual Studio 17 2022" -A ${{ matrix.architecture }} -T ClangCL -DJSON_BuildTests=On
       - name: Build
@@ -117,6 +125,15 @@ jobs:
     runs-on: windows-2022
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
+      # The module test uses `import std;`, which needs CMake's experimental
+      # import-std support. Its opt-in token is CMake-version-specific, so pin
+      # CMake to the version whose token is set in tests/module_cpp20/CMakeLists.txt.
+      - name: Get pinned CMake and ninja
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
+        with:
+          cmakeVersion: 4.3.4
       - name: Run CMake (Debug)
         run: cmake -S . -B build -G "Visual Studio 17 2022" -DJSON_CI=ON -DCMAKE_CXX_FLAGS="/permissive- /std:c++latest /utf-8 /W4 /WX"
       - name: Build

CMakeLists.txt

@@ -20,7 +20,11 @@ endif()
 ##
 ##
 set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake ${CMAKE_MODULE_PATH})
-include(ExternalProject)
+
+if (POLICY CMP0077)
+    # Allow CMake 3.13+ to override options when using FetchContent / add_subdirectory.
+    cmake_policy(SET CMP0077 NEW)
+endif ()
 
 # ---- C++ Modules Support (optional) ----
 option(NLOHMANN_JSON_BUILD_MODULES "Build C++ modules support" OFF)
@@ -38,12 +42,7 @@ endif()
 ## OPTIONS
 ##
 
-if (POLICY CMP0077)
+# VERSION_GREATER_EQUAL is not available in older CMake (< 3.7)
-    # Allow CMake 3.13+ to override options when using FetchContent / add_subdirectory.
-    cmake_policy(SET CMP0077 NEW)
-endif ()
-
-# VERSION_GREATER_EQUAL is not available in CMake 3.1
 if(${MAIN_PROJECT} AND (${CMAKE_VERSION} VERSION_EQUAL 3.13 OR ${CMAKE_VERSION} VERSION_GREATER 3.13))
     set(JSON_BuildTests_INIT ON)
 else()
@@ -98,7 +97,7 @@ if (NOT JSON_ImplicitConversions)
 endif()
 
 if (JSON_DisableEnumSerialization)
-    message(STATUS "Enum integer serialization is disabled (JSON_DISABLE_ENUM_SERIALIZATION=0)")
+    message(STATUS "Enum integer serialization is disabled (JSON_DISABLE_ENUM_SERIALIZATION=1)")
 endif()
 
 if (JSON_LegacyDiscardedValueComparison)
@@ -164,7 +163,7 @@ if (MSVC)
 endif()
 
 # Install a pkg-config file, so other tools can find this.
-CONFIGURE_FILE(
+configure_file(
     "${CMAKE_CURRENT_SOURCE_DIR}/cmake/pkg-config.pc.in"
     "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
     @ONLY
@@ -174,9 +173,11 @@ CONFIGURE_FILE(
 ## TESTS
 ## create and configure the unit test target
 ##
-if (JSON_BuildTests)
+# Only build tests when JSON_BuildTests is set and testing has not been
+# disabled by a parent project via BUILD_TESTING (see the CTest module, which
+# also calls enable_testing()).
+if (JSON_BuildTests AND (NOT DEFINED BUILD_TESTING OR BUILD_TESTING))
     include(CTest)
-    enable_testing()
     add_subdirectory(tests)
 endif()
 

FILES.md

@@ -9,6 +9,30 @@ This file describes the source for supporting files; that is, files that are not
 
 ## Continuous Integration
 
+### `.github/workflows`
+
+The [GitHub Actions](https://docs.github.com/en/actions) workflows that build, test, and analyze the library. Each file in this folder defines one workflow:
+
+- `ubuntu.yml`, `macos.yml`, `windows.yml` — build and run the test suite on Linux, macOS, and Windows.
+- `check_amalgamation.yml` — verify that the single-header amalgamation in `single_include` is up to date on pull requests.
+- `comment_check_amalgamation.yml` — comment on a pull request when the amalgamation check failed.
+- `cifuzz.yml` — run short fuzzing sessions via [OSS-Fuzz CIFuzz](https://google.github.io/oss-fuzz/getting-started/continuous-integration/) on pull requests.
+- `codeql-analysis.yml` — run [CodeQL](https://codeql.github.com) code scanning.
+- `flawfinder.yml` — run the [Flawfinder](https://dwheeler.com/flawfinder/) static analysis.
+- `semgrep.yml` — run [Semgrep](https://semgrep.dev) static analysis.
+- `scorecards.yml` — run the [OpenSSF Scorecard](https://securityscorecards.dev) supply-chain security checks.
+- `dependency-review.yml` — scan dependency changes in pull requests for known vulnerabilities.
+- `labeler.yml` — the "Pull Request Labeler" workflow (see `.github/labeler.yml`).
+- `stale.yml` — comment on and close stale issues and pull requests.
+- `publish_documentation.yml` — build and publish the documentation on every merge to the `develop` branch.
+
+Further documentation:
+
+- [Workflow syntax for GitHub Actions](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions)
+
+> [!IMPORTANT]
+> The folder `.github/workflows` is predetermined by GitHub.
+
 ### `.cirrus.yml`
 
 Configuration file for the pipeline at [Cirrus CI](https://cirrus-ci.com/github/nlohmann/json).
@@ -123,7 +147,7 @@ Further documentation:
 > [!IMPORTANT]
 > The folder `.github/ISSUE_TEMPLATE` is predetermined by GitHub.
 
-### `.github/ISSUE_TEMPLATE/config.yaml`
+### `.github/ISSUE_TEMPLATE/config.yml`
 
 Issue template chooser configuration. The file is used to configure the dialog when a new issue is created.
 
@@ -132,7 +156,7 @@ Further documentation:
 - [Configuring issue templates for your repository](https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/configuring-issue-templates-for-your-repository)
 
 > [!IMPORTANT]
-> The filename `.github/ISSUE_TEMPLATE/config.yaml` is predetermined by GitHub.
+> The filename `.github/ISSUE_TEMPLATE/config.yml` is predetermined by GitHub.
 
 ### `.github/labeler.yml`
 
@@ -165,7 +189,7 @@ Further documentation:
 - [Adding a security policy to your repository](https://docs.github.com/en/code-security/getting-started/adding-a-security-policy-to-your-repository)
 
 > [!IMPORTANT]
-> The filename `.github/SECURITY.yml` is predetermined by GitHub.
+> The filename `.github/SECURITY.md` is predetermined by GitHub.
 
 > [!NOTE]
 > The file is part of the documentation and is included in `docs/mkdocs/docs/community/security_policy.md`.
@@ -234,6 +258,16 @@ make BUILD.bazel
 
 ### `meson.build`
 
+The build definition for the [Meson](https://mesonbuild.com) build system.
+
 ### `Package.swift`
 
-### `WORKSPACE.bazel`
+The package manifest for the [Swift Package Manager](https://www.swift.org/package-manager/).
+
+### `MODULE.bazel`
+
+The module definition for [Bazel](https://bazel.build)'s [Bzlmod](https://bazel.build/external/module) dependency system. It complements `BUILD.bazel` and replaces the previously used `WORKSPACE.bazel`.
+
+Further documentation:
+
+- [Bazel modules](https://bazel.build/external/module)

Makefile

@@ -205,7 +205,7 @@ 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 WORKSPACE.bazel meson.build LICENSE.MIT
+	zip -9 --recurse-paths -X include.zip $(SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) BUILD.bazel MODULE.bazel meson.build LICENSE.MIT
 
 # Create the files for a release and add signatures and hashes.
 release: include.zip json.tar.xz

README.md

@@ -11,7 +11,7 @@
 [![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/json.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:json)
 [![Try online](https://img.shields.io/badge/try-online-blue.svg)](https://wandbox.org/permlink/1mp10JbaANo6FUc7)
 [![Documentation](https://img.shields.io/badge/docs-mkdocs-blue.svg)](https://json.nlohmann.me)
-[![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/nlohmann/json/master/LICENSE.MIT)
+[![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/nlohmann/json/develop/LICENSE.MIT)
 [![GitHub Releases](https://img.shields.io/github/release/nlohmann/json.svg)](https://github.com/nlohmann/json/releases)
 [![Packaging status](https://repology.org/badge/tiny-repos/nlohmann-json.svg)](https://repology.org/project/nlohmann-json/versions)
 [![GitHub Downloads](https://img.shields.io/github/downloads/nlohmann/json/total)](https://github.com/nlohmann/json/releases)
@@ -70,7 +70,7 @@ Other aspects were not so important to us:
 
 - **Speed**. There are certainly [faster JSON libraries](https://github.com/miloyip/nativejson-benchmark#parsing-time) out there. However, if your goal is to speed up your development by adding JSON support with a single header, then this library is the way to go. If you know how to use a `std::vector` or `std::map`, you are already set.
 
-See the [contribution guidelines](https://github.com/nlohmann/json/blob/master/.github/CONTRIBUTING.md#please-dont) for more information.
+See the [contribution guidelines](https://github.com/nlohmann/json/blob/develop/.github/CONTRIBUTING.md#please-dont) for more information.
 
 ## Sponsors
 
@@ -429,6 +429,8 @@ struct MyIterator {
     using reference = const char&;
     using iterator_category = std::input_iterator_tag;
 
+    explicit MyIterator(MyContainer* tgt = nullptr) : target(tgt) {}
+
     MyIterator& operator++() {
         target->advance();
         return *this;
@@ -450,12 +452,12 @@ MyIterator begin(MyContainer& tgt) {
 }
 
 MyIterator end(const MyContainer&) {
-    return {};
+    return MyIterator{};
 }
 
 void foo() {
     MyContainer c;
-    json j = json::parse(c);
+    json j = json::parse(begin(c), end(c));
 }
 ```
 
@@ -756,9 +758,9 @@ int i = 42;
 json jn = i;
 auto f = jn.get<double>();
 // NOT RECOMMENDED
-double f2 = jb;
+double f2 = jn;
 double f3;
-f3 = jb;
+f3 = jn;
 
 // etc.
 ```
@@ -1465,7 +1467,7 @@ I deeply appreciate the help of the following people.
 57. [Jared Grubb](https://github.com/jaredgrubb) supported the implementation of user-defined types.
 58. [EnricoBilla](https://github.com/EnricoBilla) noted a typo in an example.
 59. [Martin Hořeňovský](https://github.com/horenmar) found a way for a 2x speedup for the compilation time of the test suite.
-60. [ukhegg](https://github.com/ukhegg) found proposed an improvement for the examples section.
+60. [ukhegg](https://github.com/ukhegg) proposed an improvement for the examples section.
 61. [rswanson-ihi](https://github.com/rswanson-ihi) noted a typo in the README.
 62. [Mihai Stan](https://github.com/stanmihai4) fixed a bug in the comparison with `nullptr`s.
 63. [Tushar Maheshwari](https://github.com/tusharpm) added [cotire](https://github.com/sakra/cotire) support to speed up the compilation.
@@ -1839,7 +1841,7 @@ The library supports **Unicode input** as follows:
 This library does not support comments by default. It does so for three reasons:
 
 1. Comments are not part of the [JSON specification](https://tools.ietf.org/html/rfc8259). You may argue that `//` or `/* */` are allowed in JavaScript, but JSON is not JavaScript.
-2. This was not an oversight: Douglas Crockford [wrote on this](https://plus.google.com/118095276221607585885/posts/RK8qyGVaGSr) in May 2012:
+2. This was not an oversight: Douglas Crockford [wrote on this](https://news.ycombinator.com/item?id=3912149) in May 2012:
   
     > I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability.  I know that the lack of comments makes some people sad, but it shouldn't.
     >
@@ -1847,7 +1849,7 @@ This library does not support comments by default. It does so for three reasons:
   
 3. It is dangerous for interoperability if some libraries would add comment support while others don't. Please check [The Harmful Consequences of the Robustness Principle](https://tools.ietf.org/html/draft-iab-protocol-maintenance-01) on this.
 
-However, you can set set parameter `ignore_comments` to true in the `parse` function to ignore `//` or `/* */` comments. Comments will then be treated as whitespace.
+However, you can set parameter `ignore_comments` to true in the `parse` function to ignore `//` or `/* */` comments. Comments will then be treated as whitespace.
 
 ### Trailing commas
 

cmake/download_test_data.cmake

@@ -12,7 +12,7 @@ else()
     # create a header with the path to the downloaded test data
     file(WRITE ${CMAKE_BINARY_DIR}/include/test_data.hpp "#define TEST_DATA_DIRECTORY \"${CMAKE_BINARY_DIR}/test_files\"\n")
 
-    # download test data from GitHub release
+    # download test data from the GitHub tag source archive
     ExternalProject_Add(download_test_data_project
         URL "${JSON_TEST_DATA_URL}/archive/refs/tags/v${JSON_TEST_DATA_VERSION}.zip"
         SOURCE_DIR "${CMAKE_BINARY_DIR}/test_files"
@@ -32,14 +32,18 @@ endif()
 
 # determine the operating system (for debug and support purposes)
 find_program(UNAME_COMMAND uname)
-find_program(VER_COMMAND ver)
 find_program(LSB_RELEASE_COMMAND lsb_release)
 find_program(SW_VERS_COMMAND sw_vers)
 set(OS_VERSION_STRINGS "${CMAKE_SYSTEM}")
-if (VER_COMMAND)
+if (CMAKE_HOST_WIN32)
-    execute_process(COMMAND ${VER_COMMAND} OUTPUT_VARIABLE VER_COMMAND_RESULT OUTPUT_STRIP_TRAILING_WHITESPACE)
+    # "ver" is a cmd.exe builtin rather than a standalone executable, so it
+    # cannot be located with find_program and must be invoked through cmd
+    execute_process(COMMAND cmd /c ver OUTPUT_VARIABLE VER_COMMAND_RESULT ERROR_QUIET)
+    string(STRIP "${VER_COMMAND_RESULT}" VER_COMMAND_RESULT)
+    if (VER_COMMAND_RESULT)
         set(OS_VERSION_STRINGS "${OS_VERSION_STRINGS}; ${VER_COMMAND_RESULT}")
     endif()
+endif()
 if (SW_VERS_COMMAND)
     execute_process(COMMAND ${SW_VERS_COMMAND} OUTPUT_VARIABLE SW_VERS_COMMAND_RESULT OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_QUIET)
     string(REGEX REPLACE "[ ]*\n" "; " SW_VERS_COMMAND_RESULT "${SW_VERS_COMMAND_RESULT}")

cmake/test.cmake

@@ -35,6 +35,8 @@ foreach(feature ${CMAKE_CXX_COMPILE_FEATURES})
         set(compiler_supports_cpp_20 TRUE)
     elseif (${feature} STREQUAL cxx_std_23)
         set(compiler_supports_cpp_23 TRUE)
+    elseif (${feature} STREQUAL cxx_std_26)
+        set(compiler_supports_cpp_26 TRUE)
     endif()
 endforeach()
 
@@ -92,7 +94,6 @@ function(json_test_set_test_options tests)
             target_compile_options(${test_interface} INTERFACE ${args_COMPILE_OPTIONS})
             target_link_libraries (${test_interface} INTERFACE ${args_LINK_LIBRARIES})
             target_link_options(${test_interface} INTERFACE ${args_LINK_OPTIONS})
-            #set_target_properties(${test_interface} PROPERTIES JSON_TEST_PROPERTIES "${args_TEST_PROPERTIES}")
             set_property(DIRECTORY PROPERTY
                 ${test_interface}_TEST_PROPERTIES "${args_TEST_PROPERTIES}"
             )
@@ -102,7 +103,6 @@ endfunction()
 
 # for internal use by _json_test_add_test()
 function(_json_test_apply_test_properties test_target properties_target)
-    #get_target_property(test_properties ${properties_target} JSON_TEST_PROPERTIES)
     get_property(test_properties DIRECTORY PROPERTY ${properties_target}_TEST_PROPERTIES)
     if(test_properties)
         set_tests_properties(${test_target} PROPERTIES ${test_properties})
@@ -213,10 +213,10 @@ function(json_test_add_test_for file)
 
     if("${args_NAME}" STREQUAL "")
         get_filename_component(file_basename ${file} NAME_WE)
-        string(REGEX REPLACE "unit-([^$]+)" "test-\\1" test_name ${file_basename})
+        string(REGEX REPLACE "unit-(.+)" "test-\\1" test_name ${file_basename})
     else()
         set(test_name ${args_NAME})
-        if(NOT test_name MATCHES "test-[^$]+")
+        if(NOT test_name MATCHES "test-.+")
             message(FATAL_ERROR "Test name must start with 'test-'.")
         endif()
     endif()

docs/mkdocs/docs/api/basic_json/dump.md

@@ -27,8 +27,8 @@ and `ensure_ascii` parameters.
 `error_handler` (in)
 :   how to react on decoding errors; there are three possible values (see [`error_handler_t`](error_handler_t.md):
     `strict` (throws an exception in case a decoding error occurs; default), `replace` (replace invalid UTF-8 sequences
-    with U+FFFD), and `ignore` (ignore invalid UTF-8 sequences during serialization; all bytes are copied to the output
+    with U+FFFD), and `ignore` (ignore invalid UTF-8 sequences during serialization; all valid bytes are copied to the
-    unchanged)).
+    output unchanged, and invalid bytes are dropped)).
     
 ## Return value
 

docs/mkdocs/docs/api/basic_json/error_handler_t.md

@@ -18,7 +18,7 @@ replace
 :   replace invalid UTF-8 sequences with U+FFFD (� REPLACEMENT CHARACTER)
 
 ignore
-:   ignore invalid UTF-8 sequences; all bytes are copied to the output unchanged
+:   ignore invalid UTF-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped
 
 ## Examples
 

docs/mkdocs/docs/community/quality_assurance.md

@@ -17,9 +17,9 @@ violations will result in a failed build.
       
         | Compiler                                     | Architecture | Operating System                  | CI        |
         |----------------------------------------------|--------------|-----------------------------------|-----------|
-        | AppleClang 15.0.0.15000040; Xcode 15.0.1     | x86_64       | macOS 13.7.2 (Ventura)            | GitHub    |
+        | AppleClang 15.0.0.15000040; Xcode 15.0.1     | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000100; Xcode 15.1       | x86_64       | macOS 13.7.2 (Ventura)            | GitHub    |
+        | AppleClang 15.0.0.15000100; Xcode 15.1       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000100; Xcode 15.2       | x86_64       | macOS 13.7.2 (Ventura)            | GitHub    |
+        | AppleClang 15.0.0.15000100; Xcode 15.2       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
         | AppleClang 15.0.0.15000309; Xcode 15.3       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
         | AppleClang 15.0.0.15000309; Xcode 15.4       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
         | AppleClang 16.0.0.16000026; Xcode 16         | arm64        | macOS 15.2 (Sequoia)              | GitHub    |
@@ -28,6 +28,7 @@ violations will result in a failed build.
         | AppleClang 17.0.0.17000013; Xcode 16.3       | arm64        | macOS 15.5 (Sequoia)              | GitHub    |
         | AppleClang 17.0.0.17000013; Xcode 16.4       | arm64        | macOS 15.5 (Sequoia)              | GitHub    |
         | AppleClang 17.0.0.17000319; Xcode 26.0.1     | arm64        | macOS 15.5 (Sequoia)              | GitHub    |
+        | Clang 3.4.2                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | Clang 3.5.2                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | Clang 3.6.2                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | Clang 3.7.1                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
@@ -60,7 +61,8 @@ violations will result in a failed build.
         | Clang 19.1.7 with GNU-like command-line      | x86_64       | Windows Server 2022 (Build 20348) | GitHub    |
         | Clang 20.1.1                                 | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | Clang 20.1.8 with GNU-like command-line      | x86_64       | Windows Server 2022 (Build 20348) | GitHub    |
-        | Clang 21.0.0                                 | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
+        | Clang 21.1.8                                 | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
+        | CUDA 11.0.221 (nvcc)                         | x86_64       | Ubuntu 20.04 LTS                  | GitHub    |
         | Emscripten 4.0.6                             | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | GNU 4.8.5                                    | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | GNU 4.9.3                                    | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
@@ -79,8 +81,9 @@ violations will result in a failed build.
         | GNU 12.4.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | GNU 13.3.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | GNU 14.2.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
-        | GNU 14.2.0                                   | arm64        | Linux 6.1.100                     | Cirrus CI |
         | GNU 15.1.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
+        | GNU 16.1.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
+        | GNU 16.1.0                                   | arm64        | Linux 6.1.100                     | Cirrus CI |
         | icpc (ICC) 2021.5.0 20211109                 | x86_64       | Ubuntu 20.04.3 LTS                | GitHub    |
         | MSVC 19.0.24241.7                            | x86          | Windows 8.1                       | AppVeyor  |
         | MSVC 19.16.27035.0                           | x86          | Windows-10 (Build 14393)          | AppVeyor  |

docs/mkdocs/docs/features/comments.md

@@ -3,7 +3,7 @@
 This library does not support comments *by default*. It does so for three reasons:
 
 1. Comments are not part of the [JSON specification](https://tools.ietf.org/html/rfc8259). You may argue that `//` or `/* */` are allowed in JavaScript, but JSON is not JavaScript.
-2. This was not an oversight: Douglas Crockford [wrote on this](https://plus.google.com/118095276221607585885/posts/RK8qyGVaGSr) in May 2012:
+2. This was not an oversight: Douglas Crockford [wrote on this](https://news.ycombinator.com/item?id=3912149) in May 2012:
 
     > I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability.  I know that the lack of comments makes some people sad, but it shouldn't. 
 

include/nlohmann/json.hpp

@@ -86,6 +86,21 @@
 */
 NLOHMANN_JSON_NAMESPACE_BEGIN
 
+namespace detail
+{
+// Trait to detect std::optional<T> specializations. It is defined here rather
+// than in type_traits.hpp so that adding the <optional> include does not change
+// the include order of the C++20 module's global module fragment (the include
+// is already pulled in by the conversion headers above); see src/modules/json.cppm.
+template<typename>
+struct is_std_optional : std::false_type {};
+
+#ifdef JSON_HAS_CPP_17
+template<typename T>
+struct is_std_optional<std::optional<T>> : std::true_type {};
+#endif
+}  // namespace detail
+
 /*!
 @brief a class to store JSON values
 
@@ -1937,6 +1952,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 #endif
 #if defined(JSON_HAS_CPP_17) && JSON_HAS_STATIC_RTTI
                                                 detail::negation<std::is_same<ValueType, std::any>>,
+#endif
+#if defined(JSON_HAS_CPP_17)
+                                                // std::optional<T> can construct itself from basic_json; excluding it
+                                                // here avoids an ambiguity with that constructor (e.g., under C++26)
+                                                detail::negation<detail::is_std_optional<ValueType>>,
 #endif
                                                 detail::is_detected_lazy<detail::get_template_function, const basic_json_t&, ValueType>
                                                 >::value, int >::type = 0 >

single_include/nlohmann/json.hpp

@@ -20604,6 +20604,21 @@ NLOHMANN_JSON_NAMESPACE_END
 */
 NLOHMANN_JSON_NAMESPACE_BEGIN
 
+namespace detail
+{
+// Trait to detect std::optional<T> specializations. It is defined here rather
+// than in type_traits.hpp so that adding the <optional> include does not change
+// the include order of the C++20 module's global module fragment (the include
+// is already pulled in by the conversion headers above); see src/modules/json.cppm.
+template<typename>
+struct is_std_optional : std::false_type {};
+
+#ifdef JSON_HAS_CPP_17
+template<typename T>
+struct is_std_optional<std::optional<T>> : std::true_type {};
+#endif
+}  // namespace detail
+
 /*!
 @brief a class to store JSON values
 
@@ -22455,6 +22470,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 #endif
 #if defined(JSON_HAS_CPP_17) && JSON_HAS_STATIC_RTTI
                                                 detail::negation<std::is_same<ValueType, std::any>>,
+#endif
+#if defined(JSON_HAS_CPP_17)
+                                                // std::optional<T> can construct itself from basic_json; excluding it
+                                                // here avoids an ambiguity with that constructor (e.g., under C++26)
+                                                detail::negation<detail::is_std_optional<ValueType>>,
 #endif
                                                 detail::is_detected_lazy<detail::get_template_function, const basic_json_t&, ValueType>
                                                 >::value, int >::type = 0 >

tests/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.13...3.14)
+cmake_minimum_required(VERSION 3.13...4.0)
 
 option(JSON_Valgrind    "Execute test suite with Valgrind." OFF)
 option(JSON_FastTests   "Skip expensive/slow tests." OFF)
@@ -148,7 +148,7 @@ message(STATUS "${msg}")
 # *DO* use json_test_set_test_options() above this line
 
 json_test_should_build_32bit_test(json_32bit_test json_32bit_test_only "${JSON_32bitTest}")
-file(GLOB files src/unit-*.cpp)
+file(GLOB files CONFIGURE_DEPENDS src/unit-*.cpp)
 if(json_32bit_test_only)
     set(files src/unit-32bit.cpp)
 elseif(NOT json_32bit_test)

tests/module_cpp20/CMakeLists.txt

@@ -1,7 +1,20 @@
-cmake_minimum_required(VERSION 3.28)
+cmake_minimum_required(VERSION 3.30)
+
+# `import std;` (used by main.cpp) needs CMake's experimental C++ import-std
+# support. The accepted token is CMake-version-specific; this value matches the
+# CMake version pinned in the ci_module_cpp20 CI jobs (4.3.x). If that pin is
+# bumped, this token must be updated to match (configuration fails loudly
+# otherwise).
+set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD "451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
 
 project(json_test CXX)
 
+# import std; requires C++23 and the std library module
+set(CMAKE_CXX_STANDARD 23)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+set(CMAKE_CXX_MODULE_STD ON)
+
 set(NLOHMANN_JSON_BUILD_MODULES ON CACHE BOOL "Enable nlohmann.json module support")
 
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/../.. ${CMAKE_CURRENT_BINARY_DIR}/tests)
@@ -12,8 +25,4 @@ target_link_libraries(json_test
         nlohmann_json_modules
 )
 
-target_compile_definitions(json_test 
+target_compile_features(json_test PRIVATE cxx_std_23)
-    PRIVATE NLOHMANN_JSON_BUILD_MODULES
-)
-
-target_compile_features(json_test PUBLIC cxx_std_20)

tests/module_cpp20/main.cpp

@@ -6,9 +6,54 @@
 // SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
 // SPDX-License-Identifier: MIT
 
+import std;
 import nlohmann.json;
 
+using namespace nlohmann::literals;
+
+// Exercise the surface exported by the nlohmann.json module so that a missing
+// or broken export is caught at compile time.
+//
+// Standard-library facilities are pulled in via `import std;` rather than
+// textual `#include`s: mixing `import` with textual standard headers does not
+// compile under GCC's C++20 modules implementation, whereas `import std;` works
+// across GCC, Clang, and MSVC. This requires C++23 and CMake's (experimental)
+// import-std support; see CMakeLists.txt.
 int main()
 {
-    nlohmann::json j;
+    // basic_json / json: parsing and value access
+    nlohmann::json j = nlohmann::json::parse(R"({"a": 1, "list": [1, 2, 3]})");
+    const int a = j["a"].get<int>();
+
+    // json_pointer and operator""_json_pointer
+    nlohmann::json_pointer<std::string> ptr = "/list/2"_json_pointer;
+    const int last = j[ptr].get<int>();
+
+    // operator""_json literal
+    const nlohmann::json lit = R"([1, 2, 3])"_json;
+
+    // ordered_json
+    nlohmann::ordered_json oj;
+    oj["b"] = 2;
+    const int b = oj["b"].get<int>();
+
+    // ordered_map alias
+    nlohmann::ordered_map<std::string, int> m;
+    m["x"] = 1;
+
+    // adl_serializer (reference the exported template)
+    using serializer = nlohmann::adl_serializer<int, void>;
+    static_cast<void>(sizeof(serializer));
+
+    // to_string
+    const std::string dumped = nlohmann::to_string(j);
+
+    // operator<< (hidden friend, reached via ADL through the module)
+    std::ostringstream os;
+    os << j << oj << lit;
+
+    // use every result so the references cannot be optimized away
+    return (a == 1 && last == 3 && b == 2 && lit.size() == 3
+            && m.size() == 1 && !dumped.empty() && !os.str().empty())
+        ? 0 : 1;
 }