🔀 merge develop

#	.github/workflows/macos.yml
#	include/nlohmann/detail/input/parser.hpp
#	include/nlohmann/detail/meta/std_fs.hpp
#	include/nlohmann/json.hpp
#	single_include/nlohmann/json.hpp

.clang-tidy

@@ -1,8 +1,16 @@
+# TODO: The first three checks are only removed to get the CI going. They have to be addressed at some point.
+
 Checks: '*,
+
+         -portability-template-virtual-member-function,
+         -bugprone-use-after-move,
+         -hicpp-invalid-access-moved,
+
          -altera-id-dependent-backward-branch,
          -altera-struct-pack-align,
          -altera-unroll-loops,
          -android-cloexec-fopen,
+         -boost-use-ranges,
          -bugprone-easily-swappable-parameters,
          -cert-err58-cpp,
          -concurrency-mt-unsafe,
@@ -44,7 +52,9 @@ Checks: '*,
          -modernize-concat-nested-namespaces,
          -modernize-type-traits,
          -modernize-use-constraints,
+         -modernize-use-designated-initializers,
          -modernize-use-nodiscard,
+         -modernize-use-ranges,
          -modernize-use-std-numbers,
          -modernize-use-trailing-return-type,
          -performance-enum-size,

.github/workflows/check_amalgamation.yml

@@ -14,7 +14,7 @@ jobs:
           mkdir -p ./pr
           echo ${{ github.event.number }} > ./pr/number
           echo ${{ github.event.pull_request.user.login }} > ./pr/author
-      - uses: actions/upload-artifact@v2
+      - uses: actions/upload-artifact@v4
         with:
           name: pr
           path: pr/
@@ -33,13 +33,13 @@ jobs:
 
     steps:
       - name: Checkout pull request
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: main
           ref: ${{ github.event.pull_request.head.sha }}
 
       - name: Checkout tools
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: tools
           ref: develop

.github/workflows/cifuzz.yml

@@ -23,7 +23,7 @@ jobs:
         dry-run: false
         language: c++
     - name: Upload Crash
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       if: failure() && steps.build.outcome == 'success'
       with:
         name: artifacts

.github/workflows/codeql-analysis.yml

@@ -27,11 +27,11 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@v2
+      uses: github/codeql-action/init@v3
       with:
         languages: c-cpp
 

.github/workflows/macos.yml

@@ -17,25 +17,26 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  xcode_1:
-    runs-on: macos-11
-    strategy:
-      matrix:
-        xcode: ['11.7', '12.4', '12.5.1', '13.0']
-    env:
-      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
+# macos-11 is deprecated
+#  macos-11:
+#    runs-on: macos-11
+#    strategy:
+#      matrix:
+#        xcode: ['11.7', '12.4', '12.5.1', '13.0']
+#    env:
+#      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
+#
+#    steps:
+#      - uses: actions/checkout@v4
+#      - 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
 
-    steps:
-      - uses: actions/checkout@v3
-      - 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
-
-  xcode_2:
-    runs-on: macos-12
+  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']
@@ -43,7 +44,58 @@ jobs:
       DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
+      - 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:
+    runs-on: macos-13 # https://github.com/actions/runner-images/blob/main/images/macos/macos-13-Readme.md
+    strategy:
+      matrix:
+        xcode: [ '14.2', '14.3', '14.3.1', '15.0.1', '15.1', '15.2']
+    env:
+      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
+
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run CMake
+        run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_FastTests=ON
+      - name: Build
+        run: cmake --build build --parallel 10
+      - name: Test
+        run: cd build ; ctest -j 10 --output-on-failure
+
+  macos-14:
+    runs-on: macos-14 # https://github.com/actions/runner-images/blob/main/images/macos/macos-14-Readme.md
+    strategy:
+      matrix:
+        xcode: ['15.3', '15.4']
+    env:
+      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
+
+    steps:
+      - uses: actions/checkout@v4
+      - 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-15:
+    runs-on: macos-15 # https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
+    strategy:
+      matrix:
+        xcode: ['16.0', '16.1']
+    env:
+      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
+
+    steps:
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_FastTests=ON
       - name: Build
@@ -58,7 +110,7 @@ jobs:
         standard: [11, 14, 17, 20, 23]
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_TestStandards=${{ matrix.standard }}
       - name: Build

.github/workflows/publish_documentation.yml

@@ -23,7 +23,7 @@ jobs:
     if: github.repository == 'nlohmann/json'
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install and update PlantUML
         run: sudo apt-get update ; sudo apt-get install -y plantuml
@@ -35,7 +35,7 @@ jobs:
         run: make build -C docs/mkdocs
 
       - name: Deploy documentation
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./docs/mkdocs/site

.github/workflows/ubuntu.yml

@@ -23,9 +23,9 @@ jobs:
     steps:
       - name: Install git and unzip
         run: apt-get update ; apt-get install -y git unzip
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@v3.27.7
+        uses: lukka/get-cmake@v3.31.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -35,7 +35,7 @@ jobs:
     runs-on: ubuntu-latest
     container: ghcr.io/nlohmann/json-ci:v2.4.0
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -48,7 +48,7 @@ jobs:
       matrix:
         target: [ci_cppcheck, ci_test_valgrind, ci_test_amalgamation, ci_test_single_header, ci_single_binaries, ci_infer]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -60,9 +60,9 @@ jobs:
       matrix:
         target: [ci_cpplint, ci_reproducible_tests, ci_non_git_tests, ci_offline_testdata]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@v3.27.7
+        uses: lukka/get-cmake@v3.31.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -77,9 +77,9 @@ jobs:
     steps:
       - name: Install git, clang-tools, and unzip
         run: apt-get update ; apt-get install -y git clang-tools unzip
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@v3.27.7
+        uses: lukka/get-cmake@v3.31.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -94,9 +94,9 @@ jobs:
     steps:
       - name: Install build-essential
         run: apt-get update ; apt-get install -y build-essential unzip wget git
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@v3.27.7
+        uses: lukka/get-cmake@v3.31.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -109,7 +109,7 @@ jobs:
       contents: read
       checks: write
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -125,16 +125,30 @@ jobs:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           path-to-lcov: ${{ github.workspace }}/build/json.info.filtered.noexcept
 
+  ci_test_compilers_gcc_old:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        compiler: ['4.8', '4.9', '5', '6']
+    container: ghcr.io/nlohmann/json-ci:v2.4.0
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run CMake
+        run: CXX=g++-${{ matrix.compiler }} cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ci_test_compiler_g++-${{ matrix.compiler }}
+
   ci_test_compilers_gcc:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        compiler: ['4', '5', '6', '7', '8', '9', '10', '11', '12', 'latest']
+        # older GCC docker images (4, 5, 6) fail to check out code
+        compiler: ['7', '8', '9', '10', '11', '12', '13', '14', 'latest']
     container: gcc:${{ matrix.compiler }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@v3.27.7
+        uses: lukka/get-cmake@v3.31.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -144,14 +158,14 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        compiler: ['3.5', '3.6', '3.7', '3.8', '3.9', '4', '5', '6', '7', '8', '9', '10', '11', '12', '13', '14', '15-bullseye', 'latest']
+        compiler: ['3.5', '3.6', '3.7', '3.8', '3.9', '4', '5', '6', '7', '8', '9', '10', '11', '12', '13', '14', '15-bullseye', '16', '17', '18', '19', 'latest']
     container: silkeh/clang:${{ matrix.compiler }}
     steps:
       - name: Install unzip and git
         run: apt-get update ; apt-get install -y unzip git
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@v3.27.7
+        uses: lukka/get-cmake@v3.31.0
       - name: Set env FORCE_STDCPPFS_FLAG for clang 7 / 8 / 9 / 10
         run: echo "JSON_FORCED_GLOBAL_COMPILE_OPTIONS=-DJSON_HAS_FILESYSTEM=0;-DJSON_HAS_EXPERIMENTAL_FILESYSTEM=0" >> "$GITHUB_ENV"
         if: ${{ matrix.compiler == '7' || matrix.compiler == '8' || matrix.compiler == '9' || matrix.compiler == '10' }}
@@ -167,7 +181,7 @@ jobs:
       matrix:
         compiler: [g++-4.8]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -180,7 +194,7 @@ jobs:
       matrix:
         standard: [11, 14, 17, 20, 23]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -192,22 +206,27 @@ jobs:
     strategy:
       matrix:
         standard: [11, 14, 17, 20, 23]
+        stdlib: [libcxx, libstdcxx]
     steps:
       - name: Install git and unzip
         run: apt-get update ; apt-get install -y git unzip
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@v3.27.7
+        uses: lukka/get-cmake@v3.31.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
-      - name: Build
+      - name: Build with libc++
+        run: cmake --build build --target ci_test_clang_libcxx_cxx${{ matrix.standard }}
+        if: ${{ matrix.stdlib == 'libcxx' }}
+      - name: Build with libstdc++
         run: cmake --build build --target ci_test_clang_cxx${{ matrix.standard }}
+        if: ${{ matrix.stdlib == 'libstdcxx' }}
 
   ci_cuda_example:
     runs-on: ubuntu-latest
     container: ghcr.io/nlohmann/json-ci:v2.4.0
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -217,7 +236,7 @@ jobs:
     runs-on: ubuntu-latest
     container: ghcr.io/nlohmann/json-ci:v2.2.0
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -228,8 +247,10 @@ jobs:
   ci_reuse_compliance:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-python@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
       - name: Install REUSE tool
         run:  python -m pip install reuse
       - name: Run REUSE lint
@@ -241,7 +262,7 @@ jobs:
       matrix:
         target: [ci_test_examples, ci_test_api_documentation]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build

.github/workflows/windows.yml

@@ -24,7 +24,7 @@ jobs:
         architecture: [x64, x86]
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Set up MinGW
         uses: egor-tensin/setup-mingw@v2
         with:
@@ -45,7 +45,7 @@ jobs:
         architecture: [Win32, x64]
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Run CMake
       run: cmake -S . -B build -G "Visual Studio 16 2019" -A ${{ matrix.architecture }} -DJSON_BuildTests=On -DCMAKE_CXX_FLAGS="/W4 /WX"
       if: matrix.build_type == 'Release'
@@ -61,7 +61,7 @@ jobs:
     runs-on: windows-2019
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Run CMake
       run: cmake -S . -B build -G "Visual Studio 16 2019" -DJSON_BuildTests=On -DCMAKE_CXX_FLAGS="/permissive- /std:c++latest /utf-8 /W4 /WX"
     - name: Build
@@ -77,7 +77,7 @@ jobs:
         architecture: [Win32, x64]
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Run CMake
       run: cmake -S . -B build -G "Visual Studio 17 2022" -A ${{ matrix.architecture }} -DJSON_BuildTests=On -DCMAKE_CXX_FLAGS="/W4 /WX"
       if: matrix.build_type == 'Release'
@@ -93,7 +93,7 @@ jobs:
     runs-on: windows-2022
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Run CMake
       run: cmake -S . -B build -G "Visual Studio 17 2022" -DJSON_BuildTests=On -DCMAKE_CXX_FLAGS="/permissive- /std:c++latest /utf-8 /W4 /WX"
     - name: Build
@@ -108,7 +108,7 @@ jobs:
         version: [11, 12, 13, 14, 15]
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install Clang
         run: curl -fsSL -o LLVM${{ matrix.version }}.exe https://github.com/llvm/llvm-project/releases/download/llvmorg-${{ matrix.version }}.0.0/LLVM-${{ matrix.version }}.0.0-win64.exe ; 7z x LLVM${{ matrix.version }}.exe -y -o"C:/Program Files/LLVM"
       - name: Run CMake
@@ -125,7 +125,7 @@ jobs:
         architecture: [Win32, x64]
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run CMake
         run: cmake -S . -B build -G "Visual Studio 16 2019" -A ${{ matrix.architecture }} -T ClangCL -DJSON_BuildTests=On
       - name: Build

BUILD.bazel

@@ -49,5 +49,4 @@ cc_library(
     ],
     includes = ["include"],
     visibility = ["//visibility:public"],
-    alwayslink = True,
 )

CMakeLists.txt

@@ -210,4 +210,5 @@ if(JSON_Install)
         FILES "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
         DESTINATION ${NLOHMANN_JSON_PKGCONFIG_INSTALL_DIR}
     )
+    include(CPack)
 endif()

README.md

@@ -1111,11 +1111,11 @@ auto cbor = json::to_msgpack(j); // 0xD5 (fixext2), 0x10, 0xCA, 0xFE
 
 ## Supported compilers
 
-Though it's 2023 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work:
+Though it's 2024 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work:
 
-- GCC 4.8 - 12.0 (and possibly later)
-- Clang 3.4 - 15.0 (and possibly later)
-- Apple Clang 9.1 - 13.1 (and possibly later)
+- GCC 4.8 - 14.2 (and possibly later)
+- Clang 3.4 - 20.0 (and possibly later)
+- Apple Clang 9.1 - 16.0 (and possibly later)
 - Intel C++ Compiler 17.0.2 (and possibly later)
 - Nvidia CUDA Compiler 11.0.221 (and possibly later)
 - Microsoft Visual C++ 2015 / Build Tools 14.0.25123.0 (and possibly later)
@@ -1146,29 +1146,35 @@ The following compilers are currently used in continuous integration at [AppVeyo
 
 | Compiler                                                                                               | Operating System   | CI Provider    |
 |--------------------------------------------------------------------------------------------------------|--------------------|----------------|
-| Apple Clang 11.0.3 (clang-1103.0.32.62);  Xcode 11.7                                                   | macOS 11.7.1       | GitHub Actions |
-| Apple Clang 12.0.0 (clang-1200.0.32.29);  Xcode 12.4                                                   | macOS 11.7.1       | GitHub Actions |
-| Apple Clang 12.0.5 (clang-1205.0.22.11);  Xcode 12.5.1                                                 | macOS 11.7.1       | GitHub Actions |
-| Apple Clang 13.0.0 (clang-1300.0.29.3);   Xcode 13.0                                                   | macOS 11.7.1       | GitHub Actions |
-| Apple Clang 13.0.0 (clang-1300.0.29.3);   Xcode 13.1                                                   | macOS 12.6.1       | GitHub Actions |
-| Apple Clang 13.0.0 (clang-1300.0.29.30);  Xcode 13.2.1                                                 | macOS 12.6.1       | GitHub Actions |
-| Apple Clang 13.1.6 (clang-1316.0.21.2.3); Xcode 13.3.1                                                 | macOS 12.6.1       | GitHub Actions |
-| Apple Clang 13.1.6 (clang-1316.0.21.2.5); Xcode 13.4.1                                                 | macOS 12.6.1       | GitHub Actions |
-| Apple Clang 14.0.0 (clang-1400.0.29.102); Xcode 14.0                                                   | macOS 12.6.1       | GitHub Actions |
-| Apple Clang 14.0.0 (clang-1400.0.29.102); Xcode 14.0.1                                                 | macOS 12.6.1       | GitHub Actions |
-| Apple Clang 14.0.0 (clang-1400.0.29.202); Xcode 14.1                                                   | macOS 12.6.1       | GitHub Actions |
-| Clang 3.5.2                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 3.6.2                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 3.7.1                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 3.8.1                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 3.9.1                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 4.0.1                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 5.0.2                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 6.0.1                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 7.0.1                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 8.0.0                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 9.0.0                                                                                            | Ubuntu 20.04.3 LTS | GitHub Actions |
-| Clang 10.0.0                                                                                           | Ubuntu 20.04.3 LTS | GitHub Actions |
+| Apple Clang 13.0.0 (clang-1300.0.29.3);   Xcode 13.1                                                   | macOS 12.7.6       | GitHub Actions |
+| Apple Clang 13.0.0 (clang-1300.0.29.30);  Xcode 13.2.1                                                 | macOS 12.7.6       | GitHub Actions |
+| Apple Clang 13.1.6 (clang-1316.0.21.2.3); Xcode 13.3.1                                                 | macOS 12.7.6       | GitHub Actions |
+| Apple Clang 13.1.6 (clang-1316.0.21.2.5); Xcode 13.4.1                                                 | macOS 12.7.6       | GitHub Actions |
+| Apple Clang 14.0.0 (clang-1400.0.29.102); Xcode 14.0                                                   | macOS 12.7.6       | GitHub Actions |
+| Apple Clang 14.0.0 (clang-1400.0.29.102); Xcode 14.0.1                                                 | macOS 12.7.6       | GitHub Actions |
+| Apple Clang 14.0.0 (clang-1400.0.29.202); Xcode 14.1                                                   | macOS 12.7.6       | GitHub Actions |
+| Apple Clang 14.0.0 (clang-1400.0.29.202); Xcode 14.2                                                   | macOS 13.7         | GitHub Actions |
+| Apple Clang 14.0.3 (clang-1403.0.22.14.1); Xcode 14.3                                                  | macOS 13.7         | GitHub Actions |
+| Apple Clang 14.0.3 (clang-1403.0.22.14.1); Xcode 14.3.1                                                | macOS 13.7.1       | GitHub Actions |
+| Apple Clang 15.0.0 (clang-1500.0.40.1); Xcode 15.0.1                                                   | macOS 13.7         | GitHub Actions |
+| Apple Clang 15.0.0 (clang-1500.1.0.2.5); Xcode 15.1                                                    | macOS 13.7         | GitHub Actions |
+| Apple Clang 15.0.0 (clang-1500.1.0.2.5); Xcode 15.2                                                    | macOS 13.7         | GitHub Actions |
+| Apple Clang 15.0.0 (clang-1500.3.9.4); Xcode 15.3                                                      | macOS 14.7         | GitHub Actions |
+| Apple Clang 15.0.0 (clang-1500.3.9.4); Xcode 15.4                                                      | macOS 14.7         | GitHub Actions |
+| Apple Clang 16.0.0 (clang-1600.0.26.3); Xcode 16.0                                                     | macOS 15.0.1       | GitHub Actions |
+| Apple Clang 16.0.0 (clang-1600.0.26.4); Xcode 16.1                                                     | macOS 15.0.1       | GitHub Actions |
+| Clang 3.5.2                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 3.6.2                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 3.7.1                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 3.8.1                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 3.9.1                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 4.0.1                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 5.0.2                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 6.0.1                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 7.0.1                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 8.0.0                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 9.0.0                                                                                            | Ubuntu 22.04.1 LTS | GitHub Actions |
+| Clang 10.0.0                                                                                           | Ubuntu 22.04.1 LTS | GitHub Actions |
 | Clang 10.0.0 with GNU-like command-line                                                                | Windows-10.0.17763 | GitHub Actions |
 | Clang 11.0.0 with GNU-like command-line                                                                | Windows-10.0.17763 | GitHub Actions |
 | Clang 11.0.0 with MSVC-like command-line                                                               | Windows-10.0.17763 | GitHub Actions |
@@ -1182,20 +1188,28 @@ The following compilers are currently used in continuous integration at [AppVeyo
 | Clang 15.0.0 with GNU-like command-line                                                                | Windows-10.0.17763 | GitHub Actions |
 | Clang 15.0.4                                                                                           | Ubuntu 20.04.3 LTS | GitHub Actions |
 | Clang 16.0.0 (16.0.0-++20221031071727+500876226c60-1~exp1~20221031071831.439)                          | Ubuntu 20.04.3 LTS | GitHub Actions |
-| GCC 4.8.5 (Ubuntu 4.8.5-4ubuntu2)                                                                      | Ubuntu 20.04.3 LTS | GitHub Actions |
-| GCC 4.9.4                                                                                              | Ubuntu 20.04.3 LTS | GitHub Actions |
-| GCC 5.5.0                                                                                              | Ubuntu 20.04.3 LTS | GitHub Actions |
-| GCC 6.5.0                                                                                              | Ubuntu 20.04.3 LTS | GitHub Actions |
-| GCC 7.5.0                                                                                              | Ubuntu 20.04.3 LTS | GitHub Actions |
+| Clang 16.0.6 (++20231112084702+7cbf1a259152-1~exp1~20231112084757.16)                                  | Ubuntu 20.04.1 LTS | GitHub Actions |
+| Clang 17.0.6 (++20231208085813+6009708b4367-1~exp1~20231208085906.81)                                  | Ubuntu 20.04.1 LTS | GitHub Actions |
+| Clang 18.1.8 (++20240731024826+3b5b5c1ec4a3-1~exp1~20240731144843.145)                                 | Ubuntu 20.04.1 LTS | GitHub Actions |
+| Clang 19.1.2 (++20241016063422+7ba7d8e2f7b6-1~exp1~20241016063541.55)                                  | Ubuntu 20.04.1 LTS | GitHub Actions |
+| Clang 20.0.0 (++20241022113049+f1ade1f874db-1~exp1~20241022113104.1036)                                | Ubuntu 22.04.1 LTS | GitHub Actions |
+| GCC 4.8.5 (Ubuntu 4.8.5-4ubuntu8)                                                                      | Ubuntu 20.04.4 LTS | GitHub Actions |
+| GCC 4.9.3 (Ubuntu 4.9.3-13ubuntu2)                                                                     | Ubuntu 20.04.4 LTS | GitHub Actions |
+| GCC 4.8.5 (Ubuntu 4.8.5-4ubuntu2)                                                                      | Ubuntu 20.04.4 LTS | GitHub Actions |
+| GCC 5.5.0 (Ubuntu 5.5.0-12ubuntu1)                                                                     | Ubuntu 20.04.4 LTS | GitHub Actions |
+| GCC 6.4.0 (Ubuntu 6.4.0-17ubuntu1)                                                                     | Ubuntu 20.04.4 LTS | GitHub Actions |
+| GCC 7.5.0                                                                                              | Ubuntu 22.04.1 LTS | GitHub Actions |
 | GCC 8.1.0 (i686-posix-dwarf-rev0, Built by MinGW-W64 project)                                          | Windows-10.0.17763 | GitHub Actions |
 | GCC 8.1.0 (x86_64-posix-seh-rev0, Built by MinGW-W64 project)                                          | Windows-10.0.17763 | GitHub Actions |
-| GCC 8.5.0                                                                                              | Ubuntu 20.04.3 LTS | GitHub Actions |
-| GCC 9.5.0                                                                                              | Ubuntu 20.04.3 LTS | GitHub Actions |
-| GCC 10.4.0                                                                                             | Ubuntu 20.04.3 LTS | GitHub Actions |
+| GCC 8.5.0                                                                                              | Ubuntu 22.04.1 LTS | GitHub Actions |
+| GCC 9.5.0                                                                                              | Ubuntu 22.04.1 LTS | GitHub Actions |
+| GCC 10.5.0                                                                                             | Ubuntu 22.04.1 LTS | GitHub Actions |
 | GCC 11.1.0                                                                                             | Ubuntu (aarch64)   | Cirrus CI      |
-| GCC 11.3.0                                                                                             | Ubuntu 20.04.3 LTS | GitHub Actions |
-| GCC 12.2.0                                                                                             | Ubuntu 20.04.3 LTS | GitHub Actions |
+| GCC 11.5.0                                                                                             | Ubuntu 22.04.1 LTS | GitHub Actions |
+| GCC 12.4.0                                                                                             | Ubuntu 22.04.1 LTS | GitHub Actions |
 | GCC 13.0.0 20220605 (experimental)                                                                     | Ubuntu 20.04.3 LTS | GitHub Actions |
+| GCC 13.3.0                                                                                             | Ubuntu 22.04.1 LTS | GitHub Actions |
+| GCC 14.2.0                                                                                             | Ubuntu 22.04.1 LTS | GitHub Actions |
 | Intel C++ Compiler 2021.5.0.20211109                                                                   | Ubuntu 20.04.3 LTS | GitHub Actions |
 | NVCC 11.0.221                                                                                          | Ubuntu 20.04.3 LTS | GitHub Actions |
 | Visual Studio 14 2015 MSVC 19.0.24241.7 (Build Engine version 14.0.25420.1)                            | Windows-6.3.9600   | AppVeyor       |
@@ -1884,7 +1898,7 @@ json/tests/src/make_test_data_available.hpp:23: FATAL ERROR: REQUIRE( utils::che
 
 In case you have downloaded the library rather than checked out the code via Git, test `cmake_fetch_content_configure` will fail. Please execute `ctest -LE git_required` to skip these tests. See [issue #2189](https://github.com/nlohmann/json/issues/2189) for more information.
 
-Some tests change the installed files and hence make the whole process not reproducible. Please execute `ctest -LE not_reproducible` to skip these tests. See [issue #2324](https://github.com/nlohmann/json/issues/2324) for more information.
+Some tests change the installed files and hence make the whole process not reproducible. Please execute `ctest -LE not_reproducible` to skip these tests. See [issue #2324](https://github.com/nlohmann/json/issues/2324) for more information. Furthermore, assertions must be switched off to ensure reproducible builds (see [discussion 4494](https://github.com/nlohmann/json/discussions/4494)).
 
 Note you need to call `cmake -LE "not_reproducible|git_required"` to exclude both labels. See [issue #2596](https://github.com/nlohmann/json/issues/2596) for more information.
 

cmake/ci.cmake

@@ -13,7 +13,7 @@ execute_process(COMMAND ${ASTYLE_TOOL} --version OUTPUT_VARIABLE ASTYLE_TOOL_VER
 string(REGEX MATCH "[0-9]+(\\.[0-9]+)+" ASTYLE_TOOL_VERSION "${ASTYLE_TOOL_VERSION}")
 message(STATUS "🔖 Artistic Style ${ASTYLE_TOOL_VERSION} (${ASTYLE_TOOL})")
 
-find_program(CLANG_TOOL NAMES clang++-HEAD clang++ clang++-17 clang++-16 clang++-15 clang++-14 clang++-13 clang++-12 clang++-11 clang++)
+find_program(CLANG_TOOL NAMES clang++-HEAD clang++ clang++-20 clang++-19 clang++-18 clang++-17 clang++-16 clang++-15 clang++-14 clang++-13 clang++-12 clang++-11 clang++)
 execute_process(COMMAND ${CLANG_TOOL} --version OUTPUT_VARIABLE CLANG_TOOL_VERSION ERROR_VARIABLE CLANG_TOOL_VERSION)
 string(REGEX MATCH "[0-9]+(\\.[0-9]+)+" CLANG_TOOL_VERSION "${CLANG_TOOL_VERSION}")
 message(STATUS "🔖 Clang ${CLANG_TOOL_VERSION} (${CLANG_TOOL})")
@@ -461,6 +461,19 @@ foreach(CXX_STANDARD 11 14 17 20 23)
         COMMAND cd ${PROJECT_BINARY_DIR}/build_clang_cxx${CXX_STANDARD} && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
         COMMENT "Compile and test with Clang for C++${CXX_STANDARD}"
     )
+
+    add_custom_target(ci_test_clang_libcxx_cxx${CXX_STANDARD}
+        COMMAND CXX=${CLANG_TOOL} CXXFLAGS="${CLANG_CXXFLAGS}" ${CMAKE_COMMAND}
+            -DCMAKE_BUILD_TYPE=Debug -GNinja
+            -DJSON_BuildTests=ON -DJSON_FastTests=ON
+            -DJSON_TestStandards=${CXX_STANDARD}
+            -DCMAKE_CXX_FLAGS="-stdlib=libc++"
+            -DCMAKE_EXE_LINKER_FLAGS="-lc++abi"
+            -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_clang_cxx${CXX_STANDARD}
+        COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_clang_cxx${CXX_STANDARD}
+        COMMAND cd ${PROJECT_BINARY_DIR}/build_clang_cxx${CXX_STANDARD} && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
+        COMMENT "Compile and test with Clang for C++${CXX_STANDARD} (libc++)"
+    )
 endforeach()
 
 ###############################################################################
@@ -900,7 +913,7 @@ add_custom_target(ci_cmake_flags
 # Use more installed compilers.
 ###############################################################################
 
-foreach(COMPILER g++-4.8 g++-4.9 g++-5 g++-6 g++-7 g++-8 g++-9 g++-10 g++-11 clang++-3.5 clang++-3.6 clang++-3.7 clang++-3.8 clang++-3.9 clang++-4.0 clang++-5.0 clang++-6.0 clang++-7 clang++-8 clang++-9 clang++-10 clang++-11 clang++-12 clang++-13 clang++-14 clang++-15 clang++-16 clang++-17)
+foreach(COMPILER g++-4.8 g++-4.9 g++-5 g++-6 g++-7 g++-8 g++-9 g++-10 g++-11 clang++-3.5 clang++-3.6 clang++-3.7 clang++-3.8 clang++-3.9 clang++-4.0 clang++-5.0 clang++-6.0 clang++-7 clang++-8 clang++-9 clang++-10 clang++-11 clang++-12 clang++-13 clang++-14 clang++-15 clang++-16 clang++-17 clang++-18 clang++-19 clang++-20)
     find_program(COMPILER_TOOL NAMES ${COMPILER})
     if (COMPILER_TOOL)
         unset(ADDITIONAL_FLAGS)

include/nlohmann/detail/conversions/from_json.hpp

@@ -13,6 +13,9 @@
 #include <forward_list> // forward_list
 #include <iterator> // inserter, front_inserter, end
 #include <map> // map
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
 #include <string> // string
 #include <tuple> // tuple, make_tuple
 #include <type_traits> // is_arithmetic, is_same, is_enum, underlying_type, is_convertible
@@ -20,6 +23,7 @@
 #include <utility> // pair, declval
 #include <valarray> // valarray
 
+
 #include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
@@ -43,6 +47,24 @@ inline void from_json(const BasicJsonType& j, typename std::nullptr_t& n)
     n = nullptr;
 }
 
+#ifdef JSON_HAS_CPP_17
+#ifndef JSON_USE_IMPLICIT_CONVERSIONS
+template<typename BasicJsonType, typename T>
+void from_json(const BasicJsonType& j, std::optional<T>& opt)
+{
+    if (j.is_null())
+    {
+        opt = std::nullopt;
+    }
+    else
+    {
+        opt.emplace(j.template get<T>());
+    }
+}
+
+#endif // JSON_USE_IMPLICIT_CONVERSIONS
+#endif // JSON_HAS_CPP_17
+
 // overloads for basic_json template parameters
 template < typename BasicJsonType, typename ArithmeticType,
            enable_if_t < std::is_arithmetic<ArithmeticType>::value&&
@@ -277,7 +299,14 @@ template < typename BasicJsonType, typename T, std::size_t... Idx >
 std::array<T, sizeof...(Idx)> from_json_inplace_array_impl(BasicJsonType&& j,
         identity_tag<std::array<T, sizeof...(Idx)>> /*unused*/, index_sequence<Idx...> /*unused*/)
 {
-    return { { std::forward<BasicJsonType>(j).at(Idx).template get<T>()... } };
+    return { { std::forward<BasicJsonType>(j).at(Idx).template get < T&& > ()... } };
+}
+
+template < typename BasicJsonType, typename T, std::size_t... Idx >
+std::array<T, sizeof...(Idx)> from_json_inplace_array_impl(const BasicJsonType& j,
+        identity_tag<std::array<T, sizeof...(Idx)>> /*unused*/, index_sequence<Idx...> /*unused*/)
+{
+    return { { j.at(Idx).template get<T>()... } };
 }
 
 template < typename BasicJsonType, typename T, std::size_t N >
@@ -373,6 +402,12 @@ inline void from_json(const BasicJsonType& j, ArithmeticType& val)
     }
 }
 
+template<typename BasicJsonType, typename... Args, std::size_t... Idx>
+std::tuple<Args...> from_json_tuple_impl_base(const BasicJsonType& j, index_sequence<Idx...> /*unused*/)
+{
+    return std::make_tuple(j.at(Idx).template get<Args>()...);
+}
+
 template<typename BasicJsonType, typename... Args, std::size_t... Idx>
 std::tuple<Args...> from_json_tuple_impl_base(BasicJsonType&& j, index_sequence<Idx...> /*unused*/)
 {
@@ -382,8 +417,14 @@ std::tuple<Args...> from_json_tuple_impl_base(BasicJsonType&& j, index_sequence<
 template < typename BasicJsonType, class A1, class A2 >
 std::pair<A1, A2> from_json_tuple_impl(BasicJsonType&& j, identity_tag<std::pair<A1, A2>> /*unused*/, priority_tag<0> /*unused*/)
 {
-    return {std::forward<BasicJsonType>(j).at(0).template get<A1>(),
-            std::forward<BasicJsonType>(j).at(1).template get<A2>()};
+    return {std::forward<BasicJsonType>(j).at(0).template get < A1&& > (),
+            std::forward<BasicJsonType>(j).at(1).template get < A2&& > ()};
+}
+
+template < typename BasicJsonType, class A1, class A2 >
+std::pair<A1, A2> from_json_tuple_impl(const BasicJsonType& j, identity_tag<std::pair<A1, A2>> /*unused*/, priority_tag<0> /*unused*/)
+{
+    return {j.at(0).template get<A1>(), j.at(1).template get<A2>()};
 }
 
 template<typename BasicJsonType, typename A1, typename A2>

include/nlohmann/detail/conversions/to_chars.hpp

@@ -239,10 +239,10 @@ boundaries compute_boundaries(FloatType value)
     //                       v-     m-     v             m+            v+
 
     const bool lower_boundary_is_closer = F == 0 && E > 1;
-    const diyfp m_plus = diyfp(2 * v.f + 1, v.e - 1);
+    const diyfp m_plus = diyfp((2 * v.f) + 1, v.e - 1);
     const diyfp m_minus = lower_boundary_is_closer
-                          ? diyfp(4 * v.f - 1, v.e - 2)  // (B)
-                          : diyfp(2 * v.f - 1, v.e - 1); // (A)
+                          ? diyfp((4 * v.f) - 1, v.e - 2)  // (B)
+                          : diyfp((2 * v.f) - 1, v.e - 1); // (A)
 
     // Determine the normalized w+ = m+.
     const diyfp w_plus = diyfp::normalize(m_plus);
@@ -472,7 +472,7 @@ inline cached_power get_cached_power_for_binary_exponent(int e)
     JSON_ASSERT(e >= -1500);
     JSON_ASSERT(e <=  1500);
     const int f = kAlpha - e - 1;
-    const int k = (f * 78913) / (1 << 18) + static_cast<int>(f > 0);
+    const int k = ((f * 78913) / (1 << 18)) + static_cast<int>(f > 0);
 
     const int index = (-kCachedPowersMinDecExp + k + (kCachedPowersDecStep - 1)) / kCachedPowersDecStep;
     JSON_ASSERT(index >= 0);
@@ -950,15 +950,15 @@ inline char* append_exponent(char* buf, int e)
     }
     else if (k < 100)
     {
-        *buf++ = static_cast<char>('0' + k / 10);
+        *buf++ = static_cast<char>('0' + (k / 10));
         k %= 10;
         *buf++ = static_cast<char>('0' + k);
     }
     else
     {
-        *buf++ = static_cast<char>('0' + k / 100);
+        *buf++ = static_cast<char>('0' + (k / 100));
         k %= 100;
-        *buf++ = static_cast<char>('0' + k / 10);
+        *buf++ = static_cast<char>('0' + (k / 10));
         k %= 10;
         *buf++ = static_cast<char>('0' + k);
     }

include/nlohmann/detail/conversions/to_json.hpp

@@ -10,6 +10,9 @@
 
 #include <algorithm> // copy
 #include <iterator> // begin, end
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
 #include <string> // string
 #include <tuple> // tuple, get
 #include <type_traits> // is_same, is_constructible, is_floating_point, is_enum, underlying_type
@@ -260,6 +263,22 @@ struct external_constructor<value_t::object>
 // to_json //
 /////////////
 
+#ifdef JSON_HAS_CPP_17
+template<typename BasicJsonType, typename T,
+         enable_if_t<std::is_constructible<BasicJsonType, T>::value, int> = 0>
+void to_json(BasicJsonType& j, const std::optional<T>& opt)
+{
+    if (opt.has_value())
+    {
+        j = *opt;
+    }
+    else
+    {
+        j = nullptr;
+    }
+}
+#endif
+
 template<typename BasicJsonType, typename T,
          enable_if_t<std::is_same<T, typename BasicJsonType::boolean_t>::value, int> = 0>
 inline void to_json(BasicJsonType& j, T b) noexcept

include/nlohmann/detail/input/json_sax.hpp

@@ -353,9 +353,9 @@ class json_sax_dom_callback_parser
     using parse_event_t = typename BasicJsonType::parse_event_t;
 
     json_sax_dom_callback_parser(BasicJsonType& r,
-                                 const parser_callback_t cb,
+                                 parser_callback_t cb,
                                  const bool allow_exceptions_ = true)
-        : root(r), callback(cb), allow_exceptions(allow_exceptions_)
+        : root(r), callback(std::move(cb)), allow_exceptions(allow_exceptions_)
     {
         keep_stack.push_back(true);
     }

include/nlohmann/detail/input/lexer.hpp

@@ -967,7 +967,7 @@ class lexer : public lexer_base<BasicJsonType>
           locale's decimal point is used instead of `.` to work with the
           locale-dependent converters.
     */
-    token_type scan_number()  // lgtm [cpp/use-of-goto]
+    token_type scan_number()  // lgtm [cpp/use-of-goto] `goto` is used in this function to implement the number-parsing state machine described above. By design, any finite input will eventually reach the "done" state or return token_type::parse_error. In each intermediate state, 1 byte of the input is appended to the token_buffer vector, and only the already initialized variables token_buffer, number_type, and error_message are manipulated.
     {
         // reset token_buffer to store the number's bytes
         reset();

include/nlohmann/detail/input/parser.hpp

@@ -69,10 +69,10 @@ class parser
   public:
     /// a parser reading from an input adapter
     explicit parser(InputAdapterType&& adapter,
-                    const parser_callback_t<BasicJsonType> cb = nullptr,
+                    parser_callback_t<BasicJsonType> cb = nullptr,
                     const bool allow_exceptions_ = true,
                     const bool skip_comments = false)
-        : callback(cb)
+        : callback(std::move(cb))
         , m_lexer(std::move(adapter), skip_comments)
         , allow_exceptions(allow_exceptions_)
     {

include/nlohmann/detail/iterators/iteration_proxy.hpp

@@ -9,7 +9,7 @@
 #pragma once
 
 #include <cstddef> // size_t
-#include <iterator> // input_iterator_tag
+#include <iterator> // forward_iterator_tag
 #include <string> // string, to_string
 #include <tuple> // tuple_size, get, tuple_element
 #include <utility> // move
@@ -40,7 +40,7 @@ template<typename IteratorType> class iteration_proxy_value
     using value_type = iteration_proxy_value;
     using pointer = value_type *;
     using reference = value_type &;
-    using iterator_category = std::input_iterator_tag;
+    using iterator_category = std::forward_iterator_tag;
     using string_type = typename std::remove_cv< typename std::remove_reference<decltype( std::declval<IteratorType>().key() ) >::type >::type;
 
   private:

include/nlohmann/detail/meta/cpp_future.hpp

@@ -162,7 +162,7 @@ struct static_const
 #endif
 
 template<typename T, typename... Args>
-inline constexpr std::array<T, sizeof...(Args)> make_array(Args&& ... args)
+constexpr std::array<T, sizeof...(Args)> make_array(Args&& ... args)
 {
     return std::array<T, sizeof...(Args)> {{static_cast<T>(std::forward<Args>(args))...}};
 }

include/nlohmann/detail/meta/std_fs.hpp

@@ -19,7 +19,7 @@ namespace std_fs = std::experimental::filesystem;
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END
 #elif JSON_HAS_FILESYSTEM
-#include <filesystem>
+#include <filesystem>  // NOLINT(build/c++17)
 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
 {

include/nlohmann/detail/meta/type_traits.hpp

@@ -734,7 +734,7 @@ struct value_in_range_of_impl1<OfType, T, true>
 };
 
 template<typename OfType, typename T>
-inline constexpr bool value_in_range_of(T val)
+constexpr bool value_in_range_of(T val)
 {
     return value_in_range_of_impl1<OfType, T>::test(val);
 }
@@ -750,7 +750,7 @@ namespace impl
 {
 
 template<typename T>
-inline constexpr bool is_c_string()
+constexpr bool is_c_string()
 {
     using TUnExt = typename std::remove_extent<T>::type;
     using TUnCVExt = typename std::remove_cv<TUnExt>::type;
@@ -778,7 +778,7 @@ namespace impl
 {
 
 template<typename T>
-inline constexpr bool is_transparent()
+constexpr bool is_transparent()
 {
     return is_detected<detect_is_transparent, T>::value;
 }

include/nlohmann/detail/output/binary_writer.hpp

@@ -612,7 +612,7 @@ class binary_writer
             case value_t::binary:
             {
                 // step 0: determine if the binary type has a set subtype to
-                // determine whether or not to use the ext or fixext types
+                // determine whether to use the ext or fixext types
                 const bool use_ext = j.m_data.m_value.binary->has_subtype();
 
                 // step 1: write control byte and the byte string length

include/nlohmann/detail/output/serializer.hpp

@@ -643,7 +643,7 @@ class serializer
     @param[in] x  unsigned integer number to count its digits
     @return    number of decimal digits
     */
-    inline unsigned int count_digits(number_unsigned_t x) noexcept
+    unsigned int count_digits(number_unsigned_t x) noexcept
     {
         unsigned int n_digits = 1;
         for (;;)
@@ -926,7 +926,7 @@ class serializer
                 ? (byte & 0x3fu) | (codep << 6u)
                 : (0xFFu >> type) & (byte);
 
-        const std::size_t index = 256u + static_cast<size_t>(state) * 16u + static_cast<size_t>(type);
+        const std::size_t index = 256u + (static_cast<size_t>(state) * 16u) + static_cast<size_t>(type);
         JSON_ASSERT(index < utf8d.size());
         state = utf8d[index];
         return state;
@@ -952,7 +952,7 @@ class serializer
      * absolute values of INT_MIN and INT_MAX are usually not the same. See
      * #1708 for details.
      */
-    inline number_unsigned_t remove_sign(number_integer_t x) noexcept
+    number_unsigned_t remove_sign(number_integer_t x) noexcept
     {
         JSON_ASSERT(x < 0 && x < (std::numeric_limits<number_integer_t>::max)()); // NOLINT(misc-redundant-expression)
         return static_cast<number_unsigned_t>(-(x + 1)) + 1;

include/nlohmann/json.hpp

@@ -1029,7 +1029,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     template < class InputIT, typename std::enable_if <
                    std::is_same<InputIT, typename basic_json_t::iterator>::value ||
                    std::is_same<InputIT, typename basic_json_t::const_iterator>::value, int >::type = 0 >
-    basic_json(InputIT first, InputIT last)
+    basic_json(InputIT first, InputIT last) // NOLINT(performance-unnecessary-value-param)
     {
         JSON_ASSERT(first.m_object != nullptr);
         JSON_ASSERT(last.m_object != nullptr);
@@ -1212,15 +1212,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @brief move constructor
     /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     basic_json(basic_json&& other) noexcept
-        : json_base_class_t(std::forward<json_base_class_t>(other)),
-          m_data(std::move(other.m_data))
+    // check that passed value is valid (has to be done before forwarding)
+        : json_base_class_t((other.assert_invariant(false), std::forward<json_base_class_t>(other))),
+          m_data(std::move(other.m_data))// NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
     {
-        // check that passed value is valid
-        other.assert_invariant(false);
-
         // invalidate payload
-        other.m_data.m_type = value_t::null;
-        other.m_data.m_value = {};
+        other.m_data.m_type = value_t::null; // NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
+        other.m_data.m_value = {};// NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
 
         set_parents();
         assert_invariant();
@@ -2012,7 +2010,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it == m_data.m_value.object->end())
         {
-            JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
+            JSON_THROW(out_of_range::create(403, "key not found (key is an rvalue and cannot be shown)", this));
         }
         return set_parent(it->second);
     }
@@ -2050,7 +2048,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it == m_data.m_value.object->end())
         {
-            JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
+            JSON_THROW(out_of_range::create(403, "key not found (key is an rvalue and cannot be shown)", this));
         }
         return it->second;
     }
@@ -2116,7 +2114,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief access specified object element
     /// @sa https://json.nlohmann.me/api/basic_json/operator%5B%5D/
-    reference operator[](typename object_t::key_type key)
+    reference operator[](typename object_t::key_type key) // NOLINT(performance-unnecessary-value-param)
     {
         // implicitly convert null value to an empty object
         if (is_null())
@@ -2426,7 +2424,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     template < class IteratorType, detail::enable_if_t <
                    std::is_same<IteratorType, typename basic_json_t::iterator>::value ||
                    std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int > = 0 >
-    IteratorType erase(IteratorType pos)
+    IteratorType erase(IteratorType pos) // NOLINT(performance-unnecessary-value-param)
     {
         // make sure iterator fits the current value
         if (JSON_HEDLEY_UNLIKELY(this != pos.m_object))
@@ -2496,7 +2494,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     template < class IteratorType, detail::enable_if_t <
                    std::is_same<IteratorType, typename basic_json_t::iterator>::value ||
                    std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int > = 0 >
-    IteratorType erase(IteratorType first, IteratorType last)
+    IteratorType erase(IteratorType first, IteratorType last) // NOLINT(performance-unnecessary-value-param)
     {
         // make sure iterator fits the current value
         if (JSON_HEDLEY_UNLIKELY(this != first.m_object || this != last.m_object))
@@ -3263,7 +3261,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @note: This uses std::distance to support GCC 4.8,
     ///        see https://github.com/nlohmann/json/pull/1257
     template<typename... Args>
-    iterator insert_iterator(const_iterator pos, Args&& ... args)
+    iterator insert_iterator(const_iterator pos, Args&& ... args) // NOLINT(performance-unnecessary-value-param)
     {
         iterator result(this);
         JSON_ASSERT(m_data.m_value.array != nullptr);
@@ -3282,7 +3280,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts element into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, const basic_json& val)
+    iterator insert(const_iterator pos, const basic_json& val) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for arrays
         if (JSON_HEDLEY_LIKELY(is_array()))
@@ -3302,14 +3300,14 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts element into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, basic_json&& val)
+    iterator insert(const_iterator pos, basic_json&& val) // NOLINT(performance-unnecessary-value-param)
     {
         return insert(pos, val);
     }
 
     /// @brief inserts copies of element into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, size_type cnt, const basic_json& val)
+    iterator insert(const_iterator pos, size_type cnt, const basic_json& val) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for arrays
         if (JSON_HEDLEY_LIKELY(is_array()))
@@ -3329,7 +3327,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts range of elements into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, const_iterator first, const_iterator last)
+    iterator insert(const_iterator pos, const_iterator first, const_iterator last) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for arrays
         if (JSON_HEDLEY_UNLIKELY(!is_array()))
@@ -3360,7 +3358,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts elements from initializer list into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, initializer_list_t ilist)
+    iterator insert(const_iterator pos, initializer_list_t ilist) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for arrays
         if (JSON_HEDLEY_UNLIKELY(!is_array()))
@@ -3380,7 +3378,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts range of elements into object
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    void insert(const_iterator first, const_iterator last)
+    void insert(const_iterator first, const_iterator last) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for objects
         if (JSON_HEDLEY_UNLIKELY(!is_object()))
@@ -3412,7 +3410,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief updates a JSON object from another object, overwriting existing keys
     /// @sa https://json.nlohmann.me/api/basic_json/update/
-    void update(const_iterator first, const_iterator last, bool merge_objects = false)
+    void update(const_iterator first, const_iterator last, bool merge_objects = false) // NOLINT(performance-unnecessary-value-param)
     {
         // implicitly convert null value to an empty object
         if (is_null())
@@ -4013,12 +4011,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     template<typename InputType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json parse(InputType&& i,
-                            const parser_callback_t cb = nullptr,
+                            parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true,
                             const bool ignore_comments = false)
     {
         basic_json result;
-        parser(detail::input_adapter(std::forward<InputType>(i)), cb, allow_exceptions, ignore_comments).parse(true, result);
+        parser(detail::input_adapter(std::forward<InputType>(i)), std::move(cb), allow_exceptions, ignore_comments).parse(true, result);
         return result;
     }
 
@@ -4028,24 +4026,24 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json parse(IteratorType first,
                             IteratorType last,
-                            const parser_callback_t cb = nullptr,
+                            parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true,
                             const bool ignore_comments = false)
     {
         basic_json result;
-        parser(detail::input_adapter(std::move(first), std::move(last)), cb, allow_exceptions, ignore_comments).parse(true, result);
+        parser(detail::input_adapter(std::move(first), std::move(last)), std::move(cb), allow_exceptions, ignore_comments).parse(true, result);
         return result;
     }
 
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, parse(ptr, ptr + len))
     static basic_json parse(detail::span_input_adapter&& i,
-                            const parser_callback_t cb = nullptr,
+                            parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true,
                             const bool ignore_comments = false)
     {
         basic_json result;
-        parser(i.get(), cb, allow_exceptions, ignore_comments).parse(true, result);
+        parser(i.get(), std::move(cb), allow_exceptions, ignore_comments).parse(true, result);
         return result;
     }
 
@@ -4733,7 +4731,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         };
 
         // wrapper for "add" operation; add value at ptr
-        const auto operation_add = [&result](json_pointer & ptr, basic_json val)
+        const auto operation_add = [&result](json_pointer & ptr, const basic_json & val)
         {
             // adding to the root of the target document means replacing it
             if (ptr.empty())

single_include/nlohmann/json.hpp

@@ -41,6 +41,7 @@
 // SPDX-License-Identifier: MIT
 
 
+
 #include <utility>
 
 // #include <nlohmann/detail/abi_macros.hpp>
@@ -53,6 +54,7 @@
 // SPDX-License-Identifier: MIT
 
 
+
 // This file contains all macro definitions affecting or depending on the ABI
 
 #ifndef JSON_SKIP_LIBRARY_VERSION_CHECK
@@ -154,11 +156,15 @@
 // SPDX-License-Identifier: MIT
 
 
+
 #include <algorithm> // transform
 #include <array> // array
 #include <forward_list> // forward_list
 #include <iterator> // inserter, front_inserter, end
 #include <map> // map
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
 #include <string> // string
 #include <tuple> // tuple, make_tuple
 #include <type_traits> // is_arithmetic, is_same, is_enum, underlying_type, is_convertible
@@ -166,6 +172,7 @@
 #include <utility> // pair, declval
 #include <valarray> // valarray
 
+
 // #include <nlohmann/detail/exceptions.hpp>
 //     __ _____ _____ _____
 //  __|  |   __|     |   | |  JSON for Modern C++
@@ -176,6 +183,7 @@
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstddef> // nullptr_t
 #include <exception> // exception
 #if JSON_DIAGNOSTICS
@@ -195,6 +203,7 @@
 // SPDX-License-Identifier: MIT
 
 
+
 #include <array> // array
 #include <cstddef> // size_t
 #include <cstdint> // uint8_t
@@ -210,6 +219,7 @@
 // SPDX-License-Identifier: MIT
 
 
+
 #include <utility> // declval, pair
 // #include <nlohmann/detail/meta/detected.hpp>
 //     __ _____ _____ _____
@@ -221,6 +231,7 @@
 // SPDX-License-Identifier: MIT
 
 
+
 #include <type_traits>
 
 // #include <nlohmann/detail/meta/void_t.hpp>
@@ -233,6 +244,7 @@
 // SPDX-License-Identifier: MIT
 
 
+
 // #include <nlohmann/detail/abi_macros.hpp>
 
 
@@ -2795,7 +2807,6 @@ JSON_HEDLEY_DIAGNOSTIC_POP
     inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
     inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) }
 
-
 // inspired from https://stackoverflow.com/a/26745591
 // allows to call any std function as if (e.g. with begin):
 // using std::begin; begin(x);
@@ -2965,6 +2976,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 // #include <nlohmann/detail/abi_macros.hpp>
 
 
@@ -3039,6 +3051,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstddef> // size_t
 
 // #include <nlohmann/detail/abi_macros.hpp>
@@ -3081,6 +3094,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <array> // array
 #include <cstddef> // size_t
 #include <type_traits> // conditional, enable_if, false_type, integral_constant, is_constructible, is_integral, is_same, remove_cv, remove_reference, true_type
@@ -3235,7 +3249,7 @@ struct static_const
 #endif
 
 template<typename T, typename... Args>
-inline constexpr std::array<T, sizeof...(Args)> make_array(Args&& ... args)
+constexpr std::array<T, sizeof...(Args)> make_array(Args&& ... args)
 {
     return std::array<T, sizeof...(Args)> {{static_cast<T>(std::forward<Args>(args))...}};
 }
@@ -3253,6 +3267,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <limits> // numeric_limits
 #include <type_traits> // false_type, is_constructible, is_integral, is_same, true_type
 #include <utility> // declval
@@ -3269,6 +3284,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <iterator> // random_access_iterator_tag
 
 // #include <nlohmann/detail/abi_macros.hpp>
@@ -3336,6 +3352,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 // #include <nlohmann/detail/macro_scope.hpp>
 
 
@@ -3355,6 +3372,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 // #include <nlohmann/detail/macro_scope.hpp>
 
 
@@ -4159,7 +4177,7 @@ struct value_in_range_of_impl1<OfType, T, true>
 };
 
 template<typename OfType, typename T>
-inline constexpr bool value_in_range_of(T val)
+constexpr bool value_in_range_of(T val)
 {
     return value_in_range_of_impl1<OfType, T>::test(val);
 }
@@ -4175,7 +4193,7 @@ namespace impl
 {
 
 template<typename T>
-inline constexpr bool is_c_string()
+constexpr bool is_c_string()
 {
     using TUnExt = typename std::remove_extent<T>::type;
     using TUnCVExt = typename std::remove_cv<TUnExt>::type;
@@ -4203,7 +4221,7 @@ namespace impl
 {
 
 template<typename T>
-inline constexpr bool is_transparent()
+constexpr bool is_transparent()
 {
     return is_detected<detect_is_transparent, T>::value;
 }
@@ -4229,6 +4247,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstring> // strlen
 #include <string> // string
 #include <utility> // forward
@@ -4614,6 +4633,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 // #include <nlohmann/detail/abi_macros.hpp>
 
 
@@ -4637,6 +4657,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 // #include <nlohmann/detail/macro_scope.hpp>
 
 
@@ -4649,7 +4670,7 @@ namespace std_fs = std::experimental::filesystem;
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END
 #elif JSON_HAS_FILESYSTEM
-#include <filesystem>
+#include <filesystem> // NOLINT(build/c++17)
 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
 {
@@ -4679,6 +4700,24 @@ inline void from_json(const BasicJsonType& j, typename std::nullptr_t& n)
     n = nullptr;
 }
 
+#ifdef JSON_HAS_CPP_17
+#ifndef JSON_USE_IMPLICIT_CONVERSIONS
+template<typename BasicJsonType, typename T>
+void from_json(const BasicJsonType& j, std::optional<T>& opt)
+{
+    if (j.is_null())
+    {
+        opt = std::nullopt;
+    }
+    else
+    {
+        opt.emplace(j.template get<T>());
+    }
+}
+
+#endif // JSON_USE_IMPLICIT_CONVERSIONS
+#endif // JSON_HAS_CPP_17
+
 // overloads for basic_json template parameters
 template < typename BasicJsonType, typename ArithmeticType,
            enable_if_t < std::is_arithmetic<ArithmeticType>::value&&
@@ -4913,7 +4952,14 @@ template < typename BasicJsonType, typename T, std::size_t... Idx >
 std::array<T, sizeof...(Idx)> from_json_inplace_array_impl(BasicJsonType&& j,
         identity_tag<std::array<T, sizeof...(Idx)>> /*unused*/, index_sequence<Idx...> /*unused*/)
 {
-    return { { std::forward<BasicJsonType>(j).at(Idx).template get<T>()... } };
+    return { { std::forward<BasicJsonType>(j).at(Idx).template get < T&& > ()... } };
+}
+
+template < typename BasicJsonType, typename T, std::size_t... Idx >
+std::array<T, sizeof...(Idx)> from_json_inplace_array_impl(const BasicJsonType& j,
+        identity_tag<std::array<T, sizeof...(Idx)>> /*unused*/, index_sequence<Idx...> /*unused*/)
+{
+    return { { j.at(Idx).template get<T>()... } };
 }
 
 template < typename BasicJsonType, typename T, std::size_t N >
@@ -5009,6 +5055,12 @@ inline void from_json(const BasicJsonType& j, ArithmeticType& val)
     }
 }
 
+template<typename BasicJsonType, typename... Args, std::size_t... Idx>
+std::tuple<Args...> from_json_tuple_impl_base(const BasicJsonType& j, index_sequence<Idx...> /*unused*/)
+{
+    return std::make_tuple(j.at(Idx).template get<Args>()...);
+}
+
 template<typename BasicJsonType, typename... Args, std::size_t... Idx>
 std::tuple<Args...> from_json_tuple_impl_base(BasicJsonType&& j, index_sequence<Idx...> /*unused*/)
 {
@@ -5018,8 +5070,14 @@ std::tuple<Args...> from_json_tuple_impl_base(BasicJsonType&& j, index_sequence<
 template < typename BasicJsonType, class A1, class A2 >
 std::pair<A1, A2> from_json_tuple_impl(BasicJsonType&& j, identity_tag<std::pair<A1, A2>> /*unused*/, priority_tag<0> /*unused*/)
 {
-    return {std::forward<BasicJsonType>(j).at(0).template get<A1>(),
-            std::forward<BasicJsonType>(j).at(1).template get<A2>()};
+    return {std::forward<BasicJsonType>(j).at(0).template get < A1&& > (),
+            std::forward<BasicJsonType>(j).at(1).template get < A2&& > ()};
+}
+
+template < typename BasicJsonType, class A1, class A2 >
+std::pair<A1, A2> from_json_tuple_impl(const BasicJsonType& j, identity_tag<std::pair<A1, A2>> /*unused*/, priority_tag<0> /*unused*/)
+{
+    return {j.at(0).template get<A1>(), j.at(1).template get<A2>()};
 }
 
 template<typename BasicJsonType, typename A1, typename A2>
@@ -5142,8 +5200,12 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <algorithm> // copy
 #include <iterator> // begin, end
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
 #include <string> // string
 #include <tuple> // tuple, get
 #include <type_traits> // is_same, is_constructible, is_floating_point, is_enum, underlying_type
@@ -5161,8 +5223,9 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstddef> // size_t
-#include <iterator> // input_iterator_tag
+#include <iterator> // forward_iterator_tag
 #include <string> // string, to_string
 #include <tuple> // tuple_size, get, tuple_element
 #include <utility> // move
@@ -5196,7 +5259,7 @@ template<typename IteratorType> class iteration_proxy_value
     using value_type = iteration_proxy_value;
     using pointer = value_type *;
     using reference = value_type &;
-    using iterator_category = std::input_iterator_tag;
+    using iterator_category = std::forward_iterator_tag;
     using string_type = typename std::remove_cv< typename std::remove_reference<decltype( std::declval<IteratorType>().key() ) >::type >::type;
 
   private:
@@ -5644,6 +5707,22 @@ struct external_constructor<value_t::object>
 // to_json //
 /////////////
 
+#ifdef JSON_HAS_CPP_17
+template<typename BasicJsonType, typename T,
+         enable_if_t<std::is_constructible<BasicJsonType, T>::value, int> = 0>
+void to_json(BasicJsonType& j, const std::optional<T>& opt)
+{
+    if (opt.has_value())
+    {
+        j = *opt;
+    }
+    else
+    {
+        j = nullptr;
+    }
+}
+#endif
+
 template<typename BasicJsonType, typename T,
          enable_if_t<std::is_same<T, typename BasicJsonType::boolean_t>::value, int> = 0>
 inline void to_json(BasicJsonType& j, T b) noexcept
@@ -5882,6 +5961,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstdint> // uint8_t, uint64_t
 #include <tuple> // tie
 #include <utility> // move
@@ -5993,6 +6073,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstdint> // uint8_t
 #include <cstddef> // size_t
 #include <functional> // hash
@@ -6125,6 +6206,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <algorithm> // generate_n
 #include <array> // array
 #include <cmath> // ldexp
@@ -6150,6 +6232,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <array> // array
 #include <cstddef> // size_t
 #include <cstring> // strlen
@@ -6646,6 +6729,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstddef>
 #include <string> // string
 #include <utility> // move
@@ -6994,9 +7078,9 @@ class json_sax_dom_callback_parser
     using parse_event_t = typename BasicJsonType::parse_event_t;
 
     json_sax_dom_callback_parser(BasicJsonType& r,
-                                 const parser_callback_t cb,
+                                 parser_callback_t cb,
                                  const bool allow_exceptions_ = true)
-        : root(r), callback(cb), allow_exceptions(allow_exceptions_)
+        : root(r), callback(std::move(cb)), allow_exceptions(allow_exceptions_)
     {
         keep_stack.push_back(true);
     }
@@ -7377,6 +7461,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <array> // array
 #include <clocale> // localeconv
 #include <cstddef> // size_t
@@ -8340,7 +8425,7 @@ class lexer : public lexer_base<BasicJsonType>
           locale's decimal point is used instead of `.` to work with the
           locale-dependent converters.
     */
-    token_type scan_number()  // lgtm [cpp/use-of-goto]
+    token_type scan_number()  // lgtm [cpp/use-of-goto] `goto` is used in this function to implement the number-parsing state machine described above. By design, any finite input will eventually reach the "done" state or return token_type::parse_error. In each intermediate state, 1 byte of the input is appended to the token_buffer vector, and only the already initialized variables token_buffer, number_type, and error_message are manipulated.
     {
         // reset token_buffer to store the number's bytes
         reset();
@@ -9017,6 +9102,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstdint> // size_t
 #include <utility> // declval
 #include <string> // string
@@ -12168,6 +12254,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cmath> // isfinite
 #include <cstdint> // uint8_t
 #include <functional> // function
@@ -12237,10 +12324,10 @@ class parser
   public:
     /// a parser reading from an input adapter
     explicit parser(InputAdapterType&& adapter,
-                    const parser_callback_t<BasicJsonType> cb = nullptr,
+                    parser_callback_t<BasicJsonType> cb = nullptr,
                     const bool allow_exceptions_ = true,
                     const bool skip_comments = false)
-        : callback(cb)
+        : callback(std::move(cb))
         , m_lexer(std::move(adapter), skip_comments)
         , allow_exceptions(allow_exceptions_)
     {
@@ -12696,6 +12783,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 // #include <nlohmann/detail/abi_macros.hpp>
 
 // #include <nlohmann/detail/iterators/primitive_iterator.hpp>
@@ -12708,6 +12796,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstddef> // ptrdiff_t
 #include <limits>  // numeric_limits
 
@@ -12866,6 +12955,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <iterator> // iterator, random_access_iterator_tag, bidirectional_iterator_tag, advance, next
 #include <type_traits> // conditional, is_const, remove_const
 
@@ -13627,6 +13717,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <cstddef> // ptrdiff_t
 #include <iterator> // reverse_iterator
 #include <utility> // declval
@@ -13803,6 +13894,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <algorithm> // all_of
 #include <cctype> // isdigit
 #include <cerrno> // errno, ERANGE
@@ -14797,6 +14889,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <initializer_list>
 #include <utility>
 
@@ -14888,6 +14981,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <algorithm> // reverse
 #include <array> // array
 #include <map> // map
@@ -14913,6 +15007,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <algorithm> // copy
 #include <cstddef> // size_t
 #include <iterator> // back_inserter
@@ -15643,7 +15738,7 @@ class binary_writer
             case value_t::binary:
             {
                 // step 0: determine if the binary type has a set subtype to
-                // determine whether or not to use the ext or fixext types
+                // determine whether to use the ext or fixext types
                 const bool use_ext = j.m_data.m_value.binary->has_subtype();
 
                 // step 1: write control byte and the byte string length
@@ -16881,6 +16976,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <algorithm> // reverse, remove, fill, find, none_of
 #include <array> // array
 #include <clocale> // localeconv, lconv
@@ -16905,6 +17001,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <array> // array
 #include <cmath>   // signbit, isfinite
 #include <cstdint> // intN_t, uintN_t
@@ -17136,10 +17233,10 @@ boundaries compute_boundaries(FloatType value)
     //                       v-     m-     v             m+            v+
 
     const bool lower_boundary_is_closer = F == 0 && E > 1;
-    const diyfp m_plus = diyfp(2 * v.f + 1, v.e - 1);
+    const diyfp m_plus = diyfp((2 * v.f) + 1, v.e - 1);
     const diyfp m_minus = lower_boundary_is_closer
-                          ? diyfp(4 * v.f - 1, v.e - 2)  // (B)
-                          : diyfp(2 * v.f - 1, v.e - 1); // (A)
+                          ? diyfp((4 * v.f) - 1, v.e - 2)  // (B)
+                          : diyfp((2 * v.f) - 1, v.e - 1); // (A)
 
     // Determine the normalized w+ = m+.
     const diyfp w_plus = diyfp::normalize(m_plus);
@@ -17369,7 +17466,7 @@ inline cached_power get_cached_power_for_binary_exponent(int e)
     JSON_ASSERT(e >= -1500);
     JSON_ASSERT(e <=  1500);
     const int f = kAlpha - e - 1;
-    const int k = (f * 78913) / (1 << 18) + static_cast<int>(f > 0);
+    const int k = ((f * 78913) / (1 << 18)) + static_cast<int>(f > 0);
 
     const int index = (-kCachedPowersMinDecExp + k + (kCachedPowersDecStep - 1)) / kCachedPowersDecStep;
     JSON_ASSERT(index >= 0);
@@ -17847,15 +17944,15 @@ inline char* append_exponent(char* buf, int e)
     }
     else if (k < 100)
     {
-        *buf++ = static_cast<char>('0' + k / 10);
+        *buf++ = static_cast<char>('0' + (k / 10));
         k %= 10;
         *buf++ = static_cast<char>('0' + k);
     }
     else
     {
-        *buf++ = static_cast<char>('0' + k / 100);
+        *buf++ = static_cast<char>('0' + (k / 100));
         k %= 100;
-        *buf++ = static_cast<char>('0' + k / 10);
+        *buf++ = static_cast<char>('0' + (k / 10));
         k %= 10;
         *buf++ = static_cast<char>('0' + k);
     }
@@ -18641,7 +18738,7 @@ class serializer
     @param[in] x  unsigned integer number to count its digits
     @return    number of decimal digits
     */
-    inline unsigned int count_digits(number_unsigned_t x) noexcept
+    unsigned int count_digits(number_unsigned_t x) noexcept
     {
         unsigned int n_digits = 1;
         for (;;)
@@ -18924,7 +19021,7 @@ class serializer
                 ? (byte & 0x3fu) | (codep << 6u)
                 : (0xFFu >> type) & (byte);
 
-        const std::size_t index = 256u + static_cast<size_t>(state) * 16u + static_cast<size_t>(type);
+        const std::size_t index = 256u + (static_cast<size_t>(state) * 16u) + static_cast<size_t>(type);
         JSON_ASSERT(index < utf8d.size());
         state = utf8d[index];
         return state;
@@ -18950,7 +19047,7 @@ class serializer
      * absolute values of INT_MIN and INT_MAX are usually not the same. See
      * #1708 for details.
      */
-    inline number_unsigned_t remove_sign(number_integer_t x) noexcept
+    number_unsigned_t remove_sign(number_integer_t x) noexcept
     {
         JSON_ASSERT(x < 0 && x < (std::numeric_limits<number_integer_t>::max)()); // NOLINT(misc-redundant-expression)
         return static_cast<number_unsigned_t>(-(x + 1)) + 1;
@@ -18999,6 +19096,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // SPDX-License-Identifier: MIT
 
 
+
 #include <functional> // equal_to, less
 #include <initializer_list> // initializer_list
 #include <iterator> // input_iterator_tag, iterator_traits
@@ -20320,7 +20418,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     template < class InputIT, typename std::enable_if <
                    std::is_same<InputIT, typename basic_json_t::iterator>::value ||
                    std::is_same<InputIT, typename basic_json_t::const_iterator>::value, int >::type = 0 >
-    basic_json(InputIT first, InputIT last)
+    basic_json(InputIT first, InputIT last) // NOLINT(performance-unnecessary-value-param)
     {
         JSON_ASSERT(first.m_object != nullptr);
         JSON_ASSERT(last.m_object != nullptr);
@@ -20503,15 +20601,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @brief move constructor
     /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     basic_json(basic_json&& other) noexcept
-        : json_base_class_t(std::forward<json_base_class_t>(other)),
-          m_data(std::move(other.m_data))
+    // check that passed value is valid (has to be done before forwarding)
+        : json_base_class_t((other.assert_invariant(false), std::forward<json_base_class_t>(other))),
+          m_data(std::move(other.m_data))// NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
     {
-        // check that passed value is valid
-        other.assert_invariant(false);
-
         // invalidate payload
-        other.m_data.m_type = value_t::null;
-        other.m_data.m_value = {};
+        other.m_data.m_type = value_t::null; // NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
+        other.m_data.m_value = {};// NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
 
         set_parents();
         assert_invariant();
@@ -21303,7 +21399,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it == m_data.m_value.object->end())
         {
-            JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
+            JSON_THROW(out_of_range::create(403, "key not found (key is an rvalue and cannot be shown)", this));
         }
         return set_parent(it->second);
     }
@@ -21341,7 +21437,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it == m_data.m_value.object->end())
         {
-            JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
+            JSON_THROW(out_of_range::create(403, "key not found (key is an rvalue and cannot be shown)", this));
         }
         return it->second;
     }
@@ -21407,7 +21503,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief access specified object element
     /// @sa https://json.nlohmann.me/api/basic_json/operator%5B%5D/
-    reference operator[](typename object_t::key_type key)
+    reference operator[](typename object_t::key_type key) // NOLINT(performance-unnecessary-value-param)
     {
         // implicitly convert null value to an empty object
         if (is_null())
@@ -21717,7 +21813,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     template < class IteratorType, detail::enable_if_t <
                    std::is_same<IteratorType, typename basic_json_t::iterator>::value ||
                    std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int > = 0 >
-    IteratorType erase(IteratorType pos)
+    IteratorType erase(IteratorType pos) // NOLINT(performance-unnecessary-value-param)
     {
         // make sure iterator fits the current value
         if (JSON_HEDLEY_UNLIKELY(this != pos.m_object))
@@ -21787,7 +21883,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     template < class IteratorType, detail::enable_if_t <
                    std::is_same<IteratorType, typename basic_json_t::iterator>::value ||
                    std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int > = 0 >
-    IteratorType erase(IteratorType first, IteratorType last)
+    IteratorType erase(IteratorType first, IteratorType last) // NOLINT(performance-unnecessary-value-param)
     {
         // make sure iterator fits the current value
         if (JSON_HEDLEY_UNLIKELY(this != first.m_object || this != last.m_object))
@@ -22554,7 +22650,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @note: This uses std::distance to support GCC 4.8,
     ///        see https://github.com/nlohmann/json/pull/1257
     template<typename... Args>
-    iterator insert_iterator(const_iterator pos, Args&& ... args)
+    iterator insert_iterator(const_iterator pos, Args&& ... args) // NOLINT(performance-unnecessary-value-param)
     {
         iterator result(this);
         JSON_ASSERT(m_data.m_value.array != nullptr);
@@ -22573,7 +22669,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts element into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, const basic_json& val)
+    iterator insert(const_iterator pos, const basic_json& val) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for arrays
         if (JSON_HEDLEY_LIKELY(is_array()))
@@ -22593,14 +22689,14 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts element into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, basic_json&& val)
+    iterator insert(const_iterator pos, basic_json&& val) // NOLINT(performance-unnecessary-value-param)
     {
         return insert(pos, val);
     }
 
     /// @brief inserts copies of element into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, size_type cnt, const basic_json& val)
+    iterator insert(const_iterator pos, size_type cnt, const basic_json& val) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for arrays
         if (JSON_HEDLEY_LIKELY(is_array()))
@@ -22620,7 +22716,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts range of elements into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, const_iterator first, const_iterator last)
+    iterator insert(const_iterator pos, const_iterator first, const_iterator last) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for arrays
         if (JSON_HEDLEY_UNLIKELY(!is_array()))
@@ -22651,7 +22747,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts elements from initializer list into array
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    iterator insert(const_iterator pos, initializer_list_t ilist)
+    iterator insert(const_iterator pos, initializer_list_t ilist) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for arrays
         if (JSON_HEDLEY_UNLIKELY(!is_array()))
@@ -22671,7 +22767,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief inserts range of elements into object
     /// @sa https://json.nlohmann.me/api/basic_json/insert/
-    void insert(const_iterator first, const_iterator last)
+    void insert(const_iterator first, const_iterator last) // NOLINT(performance-unnecessary-value-param)
     {
         // insert only works for objects
         if (JSON_HEDLEY_UNLIKELY(!is_object()))
@@ -22703,7 +22799,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief updates a JSON object from another object, overwriting existing keys
     /// @sa https://json.nlohmann.me/api/basic_json/update/
-    void update(const_iterator first, const_iterator last, bool merge_objects = false)
+    void update(const_iterator first, const_iterator last, bool merge_objects = false) // NOLINT(performance-unnecessary-value-param)
     {
         // implicitly convert null value to an empty object
         if (is_null())
@@ -23304,12 +23400,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     template<typename InputType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json parse(InputType&& i,
-                            const parser_callback_t cb = nullptr,
+                            parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true,
                             const bool ignore_comments = false)
     {
         basic_json result;
-        parser(detail::input_adapter(std::forward<InputType>(i)), cb, allow_exceptions, ignore_comments).parse(true, result);
+        parser(detail::input_adapter(std::forward<InputType>(i)), std::move(cb), allow_exceptions, ignore_comments).parse(true, result);
         return result;
     }
 
@@ -23319,24 +23415,24 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json parse(IteratorType first,
                             IteratorType last,
-                            const parser_callback_t cb = nullptr,
+                            parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true,
                             const bool ignore_comments = false)
     {
         basic_json result;
-        parser(detail::input_adapter(std::move(first), std::move(last)), cb, allow_exceptions, ignore_comments).parse(true, result);
+        parser(detail::input_adapter(std::move(first), std::move(last)), std::move(cb), allow_exceptions, ignore_comments).parse(true, result);
         return result;
     }
 
     JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.8.0, parse(ptr, ptr + len))
     static basic_json parse(detail::span_input_adapter&& i,
-                            const parser_callback_t cb = nullptr,
+                            parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true,
                             const bool ignore_comments = false)
     {
         basic_json result;
-        parser(i.get(), cb, allow_exceptions, ignore_comments).parse(true, result);
+        parser(i.get(), std::move(cb), allow_exceptions, ignore_comments).parse(true, result);
         return result;
     }
 
@@ -24024,7 +24120,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         };
 
         // wrapper for "add" operation; add value at ptr
-        const auto operation_add = [&result](json_pointer & ptr, basic_json val)
+        const auto operation_add = [&result](json_pointer & ptr, const basic_json & val)
         {
             // adding to the root of the target document means replacing it
             if (ptr.empty())
@@ -24554,6 +24650,7 @@ inline void swap(nlohmann::NLOHMANN_BASIC_JSON_TPL& j1, nlohmann::NLOHMANN_BASIC
 // SPDX-License-Identifier: MIT
 
 
+
 // restore clang diagnostic settings
 #if defined(__clang__)
     #pragma clang diagnostic pop
@@ -24598,6 +24695,7 @@ inline void swap(nlohmann::NLOHMANN_BASIC_JSON_TPL& j1, nlohmann::NLOHMANN_BASIC
 // SPDX-License-Identifier: MIT
 
 
+
 #undef JSON_HEDLEY_ALWAYS_INLINE
 #undef JSON_HEDLEY_ARM_VERSION
 #undef JSON_HEDLEY_ARM_VERSION_CHECK
@@ -24748,4 +24846,5 @@ inline void swap(nlohmann::NLOHMANN_BASIC_JSON_TPL& j1, nlohmann::NLOHMANN_BASIC
 #undef JSON_HEDLEY_FALL_THROUGH
 
 
+
 #endif  // INCLUDE_NLOHMANN_JSON_HPP_

single_include/nlohmann/json_fwd.hpp

@@ -25,6 +25,7 @@
 // SPDX-License-Identifier: MIT
 
 
+
 // This file contains all macro definitions affecting or depending on the ABI
 
 #ifndef JSON_SKIP_LIBRARY_VERSION_CHECK

tests/src/unit-32bit.cpp

@@ -23,7 +23,7 @@ struct trait_test_arg
     static constexpr bool max_in_range = MaxInRange;
 };
 
-TEST_CASE_TEMPLATE_DEFINE("value_in_range_of trait", T, value_in_range_of_test)
+TEST_CASE_TEMPLATE_DEFINE("value_in_range_of trait", T, value_in_range_of_test) // NOLINT(readability-math-missing-parentheses)
 {
     using nlohmann::detail::value_in_range_of;
 

tests/src/unit-alt-string.cpp

@@ -16,8 +16,8 @@
 
 /* forward declarations */
 class alt_string;
-bool operator<(const char* op1, const alt_string& op2) noexcept;
-void int_to_string(alt_string& target, std::size_t value);
+bool operator<(const char* op1, const alt_string& op2) noexcept; // NOLINT(misc-use-internal-linkage)
+void int_to_string(alt_string& target, std::size_t value); // NOLINT(misc-use-internal-linkage)
 
 /*
  * This is virtually a string class.

tests/src/unit-bjdata.cpp

@@ -109,7 +109,7 @@ struct trait_test_arg
     static constexpr bool max_in_range = MaxInRange;
 };
 
-TEST_CASE_TEMPLATE_DEFINE("value_in_range_of trait", T, value_in_range_of_test)
+TEST_CASE_TEMPLATE_DEFINE("value_in_range_of trait", T, value_in_range_of_test) // NOLINT(readability-math-missing-parentheses)
 {
     using nlohmann::detail::value_in_range_of;
 
@@ -573,7 +573,7 @@ TEST_CASE("BJData")
 
                         // check individual bytes
                         CHECK(result[0] == 'I');
-                        auto const restored = static_cast<uint16_t>(static_cast<uint8_t>(result[2]) * 256 + static_cast<uint8_t>(result[1]));
+                        auto const restored = static_cast<uint16_t>((static_cast<uint8_t>(result[2]) * 256) + static_cast<uint8_t>(result[1]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -613,7 +613,7 @@ TEST_CASE("BJData")
 
                         // check individual bytes
                         CHECK(result[0] == 'u');
-                        auto const restored = static_cast<uint16_t>(static_cast<uint8_t>(result[2]) * 256 + static_cast<uint8_t>(result[1]));
+                        auto const restored = static_cast<uint16_t>((static_cast<uint8_t>(result[2]) * 256) + static_cast<uint8_t>(result[1]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -905,7 +905,7 @@ TEST_CASE("BJData")
 
                         // check individual bytes
                         CHECK(result[0] == 'I');
-                        auto const restored = static_cast<uint16_t>(static_cast<uint8_t>(result[2]) * 256 + static_cast<uint8_t>(result[1]));
+                        auto const restored = static_cast<uint16_t>((static_cast<uint8_t>(result[2]) * 256) + static_cast<uint8_t>(result[1]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -944,7 +944,7 @@ TEST_CASE("BJData")
 
                         // check individual bytes
                         CHECK(result[0] == 'u');
-                        auto const restored = static_cast<uint16_t>(static_cast<uint8_t>(result[2]) * 256 + static_cast<uint8_t>(result[1]));
+                        auto const restored = static_cast<uint16_t>((static_cast<uint8_t>(result[2]) * 256) + static_cast<uint8_t>(result[1]));
                         CHECK(restored == i);
 
                         // roundtrip

tests/src/unit-bson.cpp

@@ -621,7 +621,7 @@ TEST_CASE("BSON input/output_adapters")
     {
         SECTION("std::ostringstream")
         {
-            std::basic_ostringstream<std::uint8_t> ss;
+            std::basic_ostringstream<char> ss;
             json::to_bson(json_representation, ss);
             json j3 = json::from_bson(ss.str());
             CHECK(json_representation == j3);

tests/src/unit-cbor.cpp

@@ -14,7 +14,6 @@ using nlohmann::json;
 #include <fstream>
 #include <sstream>
 #include <iomanip>
-#include <iostream>
 #include <limits>
 #include <set>
 #include "make_test_data_available.hpp"
@@ -317,7 +316,7 @@ TEST_CASE("CBOR")
 
                         // check individual bytes
                         CHECK(result[0] == 0x39);
-                        const auto restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
+                        const auto restored = static_cast<uint16_t>((static_cast<uint8_t>(result[1]) * 256) + static_cast<uint8_t>(result[2]));
                         CHECK(restored == positive);
                         CHECK(-1 - restored == i);
 
@@ -505,7 +504,7 @@ TEST_CASE("CBOR")
 
                         // check individual bytes
                         CHECK(result[0] == 0x19);
-                        const auto restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
+                        const auto restored = static_cast<uint16_t>((static_cast<uint8_t>(result[1]) * 256) + static_cast<uint8_t>(result[2]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -744,7 +743,7 @@ TEST_CASE("CBOR")
 
                         // check individual bytes
                         CHECK(result[0] == 0x19);
-                        const auto restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
+                        const auto restored = static_cast<uint16_t>((static_cast<uint8_t>(result[1]) * 256) + static_cast<uint8_t>(result[2]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -990,7 +989,7 @@ TEST_CASE("CBOR")
                     {
                         0xfa, 0xff, 0x7f, 0xff, 0xff
                     };
-                    // the same with lowest float
+                    // the same with the lowest float
                     const auto result = json::to_cbor(j);
                     CHECK(result == expected);
                     // roundtrip
@@ -1881,7 +1880,7 @@ TEST_CASE("single CBOR roundtrip")
         {
             SECTION("std::ostringstream")
             {
-                std::basic_ostringstream<std::uint8_t> ss;
+                std::basic_ostringstream<char> ss;
                 json::to_cbor(j1, ss);
                 json j3 = json::from_cbor(ss.str());
                 CHECK(j1 == j3);

tests/src/unit-class_lexer.cpp

@@ -23,7 +23,7 @@ json::lexer::token_type scan_string(const char* s, const bool ignore_comments)
 }
 } // namespace
 
-std::string get_error_message(const char* s, bool ignore_comments = false);
+std::string get_error_message(const char* s, bool ignore_comments = false); // NOLINT(misc-use-internal-linkage)
 std::string get_error_message(const char* s, const bool ignore_comments)
 {
     auto ia = nlohmann::detail::input_adapter(s);

tests/src/unit-conversions.cpp

@@ -28,10 +28,30 @@ using nlohmann::json;
 #include <unordered_set>
 #include <valarray>
 
+
 // NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair
 DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
 DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
 
+#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
+    #define JSON_HAS_CPP_17
+    #define JSON_HAS_CPP_14
+#elif (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
+    #define JSON_HAS_CPP_14
+#endif
+
+#ifdef JSON_HAS_CPP_17
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
+#endif
+
+#if defined(JSON_HAS_CPP_17)
+    #include <string_view>
+#endif
+
 TEST_CASE("value conversion")
 {
     SECTION("get an object (explicit)")
@@ -153,6 +173,7 @@ TEST_CASE("value conversion")
     }
 
 #if JSON_USE_IMPLICIT_CONVERSIONS
+
     SECTION("get an object (implicit)")
     {
         const json::object_t o_reference = {{"object", json::object()},
@@ -1164,7 +1185,7 @@ TEST_CASE("value conversion")
 
             SECTION("non-const")
             {
-                const json j_const = j;
+                const json j_const = j; // NOLINT(performance-unnecessary-copy-initialization)
                 const auto& b = j_const.get_binary();
                 CHECK(*json(b).m_data.m_value.binary == *j.m_data.m_value.binary);
             }
@@ -1513,11 +1534,11 @@ NLOHMANN_JSON_SERIALIZE_ENUM(cards,
     {cards::karo, "karo"}
 })
 
-enum TaskState
+enum TaskState // NOLINT(cert-int09-c,readability-enum-initial-value)
 {
-    TS_STOPPED,
-    TS_RUNNING,
-    TS_COMPLETED,
+    TS_STOPPED = 0,
+    TS_RUNNING = 1,
+    TS_COMPLETED = 2,
     TS_INVALID = -1,
 };
 
@@ -1569,4 +1590,73 @@ TEST_CASE("JSON to enum mapping")
     }
 }
 
+
+#ifdef JSON_HAS_CPP_17
+#ifndef JSON_USE_IMPLICIT_CONVERSIONS
+TEST_CASE("std::optional")
+{
+    SECTION("null")
+    {
+        json j_null;
+        std::optional<std::string> opt_null;
+
+        CHECK(json(opt_null) == j_null);
+        CHECK(j_null.get<std::optional<std::string>>() == std::nullopt);
+    }
+
+    SECTION("string")
+    {
+        json j_string = "string";
+        std::optional<std::string> opt_string = "string";
+
+        CHECK(json(opt_string) == j_string);
+        CHECK(std::optional<std::string>(j_string) == opt_string);
+    }
+
+    SECTION("bool")
+    {
+        json j_bool = true;
+        std::optional<bool> opt_bool = true;
+
+        CHECK(json(opt_bool) == j_bool);
+        CHECK(std::optional<bool>(j_bool) == opt_bool);
+    }
+
+    SECTION("number")
+    {
+        json j_number = 1;
+        std::optional<int> opt_int = 1;
+
+        CHECK(json(opt_int) == j_number);
+        CHECK(j_number.get<std::optional<int>>() == opt_int);
+    }
+
+    SECTION("array")
+    {
+        json j_array = {1, 2, nullptr};
+        std::vector<std::optional<int>> opt_array = {{1, 2, std::nullopt}};
+
+        CHECK(json(opt_array) == j_array);
+        CHECK(j_array.get<std::vector<std::optional<int>>>() == opt_array);
+    }
+
+    SECTION("object")
+    {
+        json j_object = {{"one", 1}, {"two", 2}, {"zero", nullptr}};
+        std::map<std::string, std::optional<int>> opt_object {{"one", 1}, {"two", 2}, {"zero", std::nullopt}};
+
+        CHECK(json(opt_object) == j_object);
+        CHECK(std::map<std::string, std::optional<int>>(j_object) == opt_object);
+    }
+}
+#endif
+#endif
+
+#ifdef JSON_HAS_CPP_17
+    #undef JSON_HAS_CPP_17
+#endif
+
+#ifdef JSON_HAS_CPP_14
+    #undef JSON_HAS_CPP_14
+#endif
 DOCTEST_CLANG_SUPPRESS_WARNING_POP

tests/src/unit-deserialization.cpp

@@ -20,6 +20,7 @@ using nlohmann::json;
 #include <sstream>
 #include <valarray>
 
+
 namespace
 {
 struct SaxEventLogger : public nlohmann::json_sax<json>
@@ -1131,13 +1132,15 @@ TEST_CASE("deserialization")
     }
 }
 
-TEST_CASE_TEMPLATE("deserialization of different character types (ASCII)", T,
-                   char, unsigned char, signed char,
-                   wchar_t,
-                   char16_t, char32_t,
-                   std::uint8_t, std::int8_t,
-                   std::int16_t, std::uint16_t,
-                   std::int32_t, std::uint32_t)
+// select the types to test - char8_t is only available in C++20
+#define TYPE_LIST(...) __VA_ARGS__
+#ifdef JSON_HAS_CPP_20
+    #define ASCII_TYPES TYPE_LIST(char, wchar_t, char16_t, char32_t, char8_t)
+#else
+    #define ASCII_TYPES TYPE_LIST(char, wchar_t, char16_t, char32_t)
+#endif
+
+TEST_CASE_TEMPLATE("deserialization of different character types (ASCII)", T, ASCII_TYPES) // NOLINT(readability-math-missing-parentheses)
 {
     std::vector<T> const v = {'t', 'r', 'u', 'e'};
     CHECK(json::parse(v) == json(true));
@@ -1149,8 +1152,8 @@ TEST_CASE_TEMPLATE("deserialization of different character types (ASCII)", T,
     CHECK(l.events == std::vector<std::string>({"boolean(true)"}));
 }
 
-TEST_CASE_TEMPLATE("deserialization of different character types (UTF-8)", T,
-                   char, unsigned char, std::uint8_t)
+TEST_CASE_TEMPLATE("deserialization of different character types (UTF-8)", T, // NOLINT(readability-math-missing-parentheses)
+                   char, unsigned char, std::uint8_t)// NOLINT(readability-math-missing-parentheses)
 {
     // a star emoji
     std::vector<T> const v = {'"', static_cast<T>(0xe2u), static_cast<T>(0xadu), static_cast<T>(0x90u), static_cast<T>(0xefu), static_cast<T>(0xb8u), static_cast<T>(0x8fu), '"'};
@@ -1162,8 +1165,8 @@ TEST_CASE_TEMPLATE("deserialization of different character types (UTF-8)", T,
     CHECK(l.events.size() == 1);
 }
 
-TEST_CASE_TEMPLATE("deserialization of different character types (UTF-16)", T,
-                   char16_t, std::uint16_t)
+TEST_CASE_TEMPLATE("deserialization of different character types (UTF-16)", T, // NOLINT(readability-math-missing-parentheses)
+                   char16_t) // NOLINT(readability-math-missing-parentheses)
 {
     // a star emoji
     std::vector<T> const v = {static_cast<T>('"'), static_cast<T>(0x2b50), static_cast<T>(0xfe0f), static_cast<T>('"')};
@@ -1175,8 +1178,8 @@ TEST_CASE_TEMPLATE("deserialization of different character types (UTF-16)", T,
     CHECK(l.events.size() == 1);
 }
 
-TEST_CASE_TEMPLATE("deserialization of different character types (UTF-32)", T,
-                   char32_t, std::uint32_t)
+TEST_CASE_TEMPLATE("deserialization of different character types (UTF-32)", T, // NOLINT(readability-math-missing-parentheses)
+                   char32_t) // NOLINT(readability-math-missing-parentheses)
 {
     // a star emoji
     std::vector<T> const v = {static_cast<T>('"'), static_cast<T>(0x2b50), static_cast<T>(0xfe0f), static_cast<T>('"')};

tests/src/unit-diagnostics.cpp

@@ -39,7 +39,12 @@ TEST_CASE("Better diagnostics")
     {
         json j;
         j["object"]["object"] = true;
+
+#if defined(JSON_HAS_CPP_17)
+        CHECK_THROWS_WITH_AS(j["object"].at("not_found"), "[json.exception.out_of_range.403] (/object) key not found (key is an rvalue and cannot be shown)", json::out_of_range);
+#else
         CHECK_THROWS_WITH_AS(j["object"].at("not_found"), "[json.exception.out_of_range.403] (/object) key 'not_found' not found", json::out_of_range);
+#endif
     }
 
     SECTION("array index out of range")

tests/src/unit-element_access1.cpp

@@ -55,7 +55,7 @@ TEST_CASE("element access 1")
                 SECTION("null")
                 {
                     json j_nonarray(json::value_t::null);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
 
                     CHECK_THROWS_WITH_AS(j_nonarray.at(0), "[json.exception.type_error.304] cannot use at() with null", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const.at(0), "[json.exception.type_error.304] cannot use at() with null", json::type_error&);
@@ -64,7 +64,7 @@ TEST_CASE("element access 1")
                 SECTION("boolean")
                 {
                     json j_nonarray(json::value_t::boolean);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
 
                     CHECK_THROWS_WITH_AS(j_nonarray.at(0), "[json.exception.type_error.304] cannot use at() with boolean", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const.at(0), "[json.exception.type_error.304] cannot use at() with boolean", json::type_error&);
@@ -73,7 +73,7 @@ TEST_CASE("element access 1")
                 SECTION("string")
                 {
                     json j_nonarray(json::value_t::string);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
 
                     CHECK_THROWS_WITH_AS(j_nonarray.at(0), "[json.exception.type_error.304] cannot use at() with string", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const.at(0), "[json.exception.type_error.304] cannot use at() with string", json::type_error&);
@@ -82,7 +82,7 @@ TEST_CASE("element access 1")
                 SECTION("object")
                 {
                     json j_nonarray(json::value_t::object);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
 
                     CHECK_THROWS_WITH_AS(j_nonarray.at(0), "[json.exception.type_error.304] cannot use at() with object", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const.at(0), "[json.exception.type_error.304] cannot use at() with object", json::type_error&);
@@ -91,7 +91,7 @@ TEST_CASE("element access 1")
                 SECTION("number (integer)")
                 {
                     json j_nonarray(json::value_t::number_integer);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
 
                     CHECK_THROWS_WITH_AS(j_nonarray.at(0), "[json.exception.type_error.304] cannot use at() with number", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const.at(0), "[json.exception.type_error.304] cannot use at() with number", json::type_error&);
@@ -100,7 +100,7 @@ TEST_CASE("element access 1")
                 SECTION("number (unsigned)")
                 {
                     json j_nonarray(json::value_t::number_unsigned);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
 
                     CHECK_THROWS_WITH_AS(j_nonarray.at(0), "[json.exception.type_error.304] cannot use at() with number", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const.at(0), "[json.exception.type_error.304] cannot use at() with number", json::type_error&);
@@ -109,7 +109,7 @@ TEST_CASE("element access 1")
                 SECTION("number (floating-point)")
                 {
                     json j_nonarray(json::value_t::number_float);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray);  // NOLINT(performance-unnecessary-copy-initialization)
 
                     CHECK_THROWS_WITH_AS(j_nonarray.at(0), "[json.exception.type_error.304] cannot use at() with number", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const.at(0), "[json.exception.type_error.304] cannot use at() with number", json::type_error&);
@@ -155,7 +155,7 @@ TEST_CASE("element access 1")
                     SECTION("standard tests")
                     {
                         json j_nonarray(json::value_t::null);
-                        const json j_nonarray_const(j_nonarray);
+                        const json j_nonarray_const(j_nonarray);  // NOLINT(performance-unnecessary-copy-initialization)
                         CHECK_NOTHROW(j_nonarray[0]);
                         CHECK_THROWS_WITH_AS(j_nonarray_const[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with null", json::type_error&);
                     }
@@ -171,7 +171,7 @@ TEST_CASE("element access 1")
                 SECTION("boolean")
                 {
                     json j_nonarray(json::value_t::boolean);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonarray[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with boolean", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with boolean", json::type_error&);
                 }
@@ -179,7 +179,7 @@ TEST_CASE("element access 1")
                 SECTION("string")
                 {
                     json j_nonarray(json::value_t::string);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonarray[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with string", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with string", json::type_error&);
                 }
@@ -187,7 +187,7 @@ TEST_CASE("element access 1")
                 SECTION("object")
                 {
                     json j_nonarray(json::value_t::object);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonarray[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with object", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with object", json::type_error&);
                 }
@@ -195,7 +195,7 @@ TEST_CASE("element access 1")
                 SECTION("number (integer)")
                 {
                     json j_nonarray(json::value_t::number_integer);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonarray[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with number", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with number", json::type_error&);
                 }
@@ -203,7 +203,7 @@ TEST_CASE("element access 1")
                 SECTION("number (unsigned)")
                 {
                     json j_nonarray(json::value_t::number_unsigned);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonarray[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with number", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with number", json::type_error&);
                 }
@@ -211,7 +211,7 @@ TEST_CASE("element access 1")
                 SECTION("number (floating-point)")
                 {
                     json j_nonarray(json::value_t::number_float);
-                    const json j_nonarray_const(j_nonarray);
+                    const json j_nonarray_const(j_nonarray); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonarray[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with number", json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonarray_const[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with number", json::type_error&);
                 }

tests/src/unit-element_access2.cpp

@@ -17,7 +17,7 @@
 // build test with C++14
 // JSON_HAS_CPP_14
 
-TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_json)
+TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_json) // NOLINT(readability-math-missing-parentheses)
 {
     SECTION("object")
     {
@@ -69,12 +69,17 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
 
             SECTION("access outside bounds")
             {
+#if defined(JSON_HAS_CPP_17)
+                CHECK_THROWS_WITH_AS(j.at("foo"), "[json.exception.out_of_range.403] key not found (key is an rvalue and cannot be shown)", typename Json::out_of_range&);
+                CHECK_THROWS_WITH_AS(j_const.at("foo"), "[json.exception.out_of_range.403] key not found (key is an rvalue and cannot be shown)", typename Json::out_of_range&);
+#else
                 CHECK_THROWS_WITH_AS(j.at("foo"), "[json.exception.out_of_range.403] key 'foo' not found", typename Json::out_of_range&);
                 CHECK_THROWS_WITH_AS(j_const.at("foo"), "[json.exception.out_of_range.403] key 'foo' not found", typename Json::out_of_range&);
+#endif
 
 #ifdef JSON_HAS_CPP_17
-                CHECK_THROWS_WITH_AS(j.at(std::string_view("foo")), "[json.exception.out_of_range.403] key 'foo' not found", typename Json::out_of_range&);
-                CHECK_THROWS_WITH_AS(j_const.at(std::string_view("foo")), "[json.exception.out_of_range.403] key 'foo' not found", typename Json::out_of_range&);
+                CHECK_THROWS_WITH_AS(j.at(std::string_view("foo")), "[json.exception.out_of_range.403] key not found (key is an rvalue and cannot be shown)", typename Json::out_of_range&);
+                CHECK_THROWS_WITH_AS(j_const.at(std::string_view("foo")), "[json.exception.out_of_range.403] key not found (key is an rvalue and cannot be shown)", typename Json::out_of_range&);
 #endif
             }
 
@@ -83,7 +88,7 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
                 SECTION("null")
                 {
                     Json j_nonobject(Json::value_t::null);
-                    const Json j_nonobject_const(j_nonobject);
+                    const Json j_nonobject_const(j_nonobject); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonobject.at("foo"), "[json.exception.type_error.304] cannot use at() with null", typename Json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonobject_const.at("foo"), "[json.exception.type_error.304] cannot use at() with null", typename Json::type_error&);
 
@@ -96,7 +101,7 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
                 SECTION("boolean")
                 {
                     Json j_nonobject(Json::value_t::boolean);
-                    const Json j_nonobject_const(j_nonobject);
+                    const Json j_nonobject_const(j_nonobject); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonobject.at("foo"), "[json.exception.type_error.304] cannot use at() with boolean", typename Json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonobject_const.at("foo"), "[json.exception.type_error.304] cannot use at() with boolean", typename Json::type_error&);
 
@@ -109,7 +114,7 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
                 SECTION("string")
                 {
                     Json j_nonobject(Json::value_t::string);
-                    const Json j_nonobject_const(j_nonobject);
+                    const Json j_nonobject_const(j_nonobject); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonobject.at("foo"), "[json.exception.type_error.304] cannot use at() with string", typename Json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonobject_const.at("foo"), "[json.exception.type_error.304] cannot use at() with string", typename Json::type_error&);
 
@@ -122,7 +127,7 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
                 SECTION("array")
                 {
                     Json j_nonobject(Json::value_t::array);
-                    const Json j_nonobject_const(j_nonobject);
+                    const Json j_nonobject_const(j_nonobject); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonobject.at("foo"), "[json.exception.type_error.304] cannot use at() with array", typename Json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonobject_const.at("foo"), "[json.exception.type_error.304] cannot use at() with array", typename Json::type_error&);
 
@@ -135,7 +140,7 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
                 SECTION("number (integer)")
                 {
                     Json j_nonobject(Json::value_t::number_integer);
-                    const Json j_nonobject_const(j_nonobject);
+                    const Json j_nonobject_const(j_nonobject); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonobject.at("foo"), "[json.exception.type_error.304] cannot use at() with number", typename Json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonobject_const.at("foo"), "[json.exception.type_error.304] cannot use at() with number", typename Json::type_error&);
 
@@ -148,7 +153,7 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
                 SECTION("number (unsigned)")
                 {
                     Json j_nonobject(Json::value_t::number_unsigned);
-                    const Json j_nonobject_const(j_nonobject);
+                    const Json j_nonobject_const(j_nonobject); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonobject.at("foo"), "[json.exception.type_error.304] cannot use at() with number", typename Json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonobject_const.at("foo"), "[json.exception.type_error.304] cannot use at() with number", typename Json::type_error&);
 
@@ -161,7 +166,7 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
                 SECTION("number (floating-point)")
                 {
                     Json j_nonobject(Json::value_t::number_float);
-                    const Json j_nonobject_const(j_nonobject);
+                    const Json j_nonobject_const(j_nonobject); // NOLINT(performance-unnecessary-copy-initialization)
                     CHECK_THROWS_WITH_AS(j_nonobject.at("foo"), "[json.exception.type_error.304] cannot use at() with number", typename Json::type_error&);
                     CHECK_THROWS_WITH_AS(j_nonobject_const.at("foo"), "[json.exception.type_error.304] cannot use at() with number", typename Json::type_error&);
 
@@ -1456,7 +1461,7 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
 }
 
 #if !defined(JSON_NOEXCEPTION)
-TEST_CASE_TEMPLATE("element access 2 (throwing tests)", Json, nlohmann::json, nlohmann::ordered_json)
+TEST_CASE_TEMPLATE("element access 2 (throwing tests)", Json, nlohmann::json, nlohmann::ordered_json) // NOLINT(readability-math-missing-parentheses)
 {
     SECTION("object")
     {
@@ -1492,7 +1497,7 @@ TEST_CASE_TEMPLATE("element access 2 (throwing tests)", Json, nlohmann::json, nl
 #endif
 
 // TODO(falbrechtskirchinger) merge with the other test case; clean up
-TEST_CASE_TEMPLATE("element access 2 (additional value() tests)", Json, nlohmann::json, nlohmann::ordered_json)
+TEST_CASE_TEMPLATE("element access 2 (additional value() tests)", Json, nlohmann::json, nlohmann::ordered_json) // NOLINT(readability-math-missing-parentheses)
 {
     using string_t = typename Json::string_t;
     using number_integer_t = typename Json::number_integer_t;

tests/src/unit-json_patch.cpp

@@ -1305,7 +1305,7 @@ TEST_CASE("JSON patch")
                 const auto& doc = test["doc"];
                 const auto& patch = test["patch"];
 
-                if (test.count("error") == 0)
+                if (test.count("error") == 0) // NOLINT(readability-container-contains)
                 {
                     // if an expected value is given, use it; use doc otherwise
                     const auto& expected = test.value("expected", doc);

tests/src/unit-msgpack.cpp

@@ -281,7 +281,7 @@ TEST_CASE("MessagePack")
 
                         // check individual bytes
                         CHECK(result[0] == 0xcd);
-                        auto const restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
+                        auto const restored = static_cast<uint16_t>((static_cast<uint8_t>(result[1]) * 256) + static_cast<uint8_t>(result[2]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -671,7 +671,7 @@ TEST_CASE("MessagePack")
 
                         // check individual bytes
                         CHECK(result[0] == 0xcd);
-                        auto const restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
+                        auto const restored = static_cast<uint16_t>((static_cast<uint8_t>(result[1]) * 256) + static_cast<uint8_t>(result[2]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -1604,7 +1604,7 @@ TEST_CASE("single MessagePack roundtrip")
         {
             SECTION("std::ostringstream")
             {
-                std::basic_ostringstream<std::uint8_t> ss;
+                std::basic_ostringstream<char> ss;
                 json::to_msgpack(j1, ss);
                 json j3 = json::from_msgpack(ss.str());
                 CHECK(j1 == j3);

tests/src/unit-readme.cpp

@@ -171,7 +171,7 @@ TEST_CASE("README" * doctest::skip())
 
             // find an entry
             CHECK(o.find("foo") != o.end());
-            if (o.find("foo") != o.end())
+            if (o.find("foo") != o.end()) // NOLINT(readability-container-contains)
             {
                 // there is an entry with key "foo"
             }

tests/src/unit-regression2.cpp

@@ -94,14 +94,14 @@ struct Data
     std::string b{}; // NOLINT(readability-redundant-member-init)
 };
 
-void from_json(const json& j, Data& data);
+void from_json(const json& j, Data& data); // NOLINT(misc-use-internal-linkage)
 void from_json(const json& j, Data& data)
 {
     j["a"].get_to(data.a);
     j["b"].get_to(data.b);
 }
 
-bool operator==(Data const& lhs, Data const& rhs);
+bool operator==(Data const& lhs, Data const& rhs); // NOLINT(misc-use-internal-linkage)
 bool operator==(Data const& lhs, Data const& rhs)
 {
     return lhs.a == rhs.a && lhs.b == rhs.b;
@@ -221,7 +221,7 @@ class FooBar
     Foo foo{}; // NOLINT(readability-redundant-member-init)
 };
 
-inline void from_json(const nlohmann::json& j, FooBar& fb)
+inline void from_json(const nlohmann::json& j, FooBar& fb) // NOLINT(misc-use-internal-linkage)
 {
     j.at("value").get_to(fb.foo.value);
 }
@@ -249,7 +249,7 @@ struct for_3171_derived : public for_3171_base
     explicit for_3171_derived(const std::string& /*unused*/) { }
 };
 
-inline void from_json(const json& j, for_3171_base& tb)
+inline void from_json(const json& j, for_3171_base& tb) // NOLINT(misc-use-internal-linkage)
 {
     tb._from_json(j);
 }
@@ -264,7 +264,7 @@ struct for_3312
     std::string name;
 };
 
-inline void from_json(const json& j, for_3312& obj)
+inline void from_json(const json& j, for_3312& obj) // NOLINT(misc-use-internal-linkage)
 {
     j.at("name").get_to(obj.name);
 }
@@ -675,6 +675,7 @@ TEST_CASE("regression tests 2")
     }
 
 #ifdef JSON_HAS_CPP_20
+#ifndef _LIBCPP_VERSION // see https://github.com/nlohmann/json/issues/4490
 #if __has_include(<span>)
     SECTION("issue #2546 - parsing containers of std::byte")
     {
@@ -684,6 +685,7 @@ TEST_CASE("regression tests 2")
         CHECK(j.dump() == "\"Hello, world!\"");
     }
 #endif
+#endif
 #endif
 
     SECTION("issue #2574 - Deserialization to std::array, std::pair, and std::tuple with non-default constructable types fails")

tests/src/unit-serialization.cpp

@@ -165,7 +165,7 @@ TEST_CASE("serialization")
     }
 }
 
-TEST_CASE_TEMPLATE("serialization for extreme integer values", T, int32_t, uint32_t, int64_t, uint64_t)
+TEST_CASE_TEMPLATE("serialization for extreme integer values", T, int32_t, uint32_t, int64_t, uint64_t) // NOLINT(readability-math-missing-parentheses)
 {
     SECTION("minimum")
     {

tests/src/unit-testsuites.cpp

@@ -163,7 +163,7 @@ TEST_CASE("compliance tests from nativejson-benchmark")
         TEST_DOUBLE("[2.2250738585072012e-308]",
                     2.2250738585072014e-308);
 
-        // More closer to normal/subnormal boundary
+        // Closer to normal/subnormal boundary
         // boundary = 2^-1022 - 2^-1075 = 2.225073858507201136057409796709131975934819546351645648... ¡Á 10^-308
         TEST_DOUBLE("[2.22507385850720113605740979670913197593481954635164564e-308]",
                     2.2250738585072009e-308);
@@ -312,7 +312,7 @@ TEST_CASE("test suite from json-test-suite")
 {
     SECTION("read all sample.json")
     {
-        // read a file with all unicode characters stored as single-character
+        // read a file with all Unicode characters stored as single-character
         // strings in a JSON array
         std::ifstream f(TEST_DATA_DIRECTORY "/json_testsuite/sample.json");
         json j;

tests/src/unit-ubjson.cpp

@@ -450,7 +450,7 @@ TEST_CASE("UBJSON")
 
                         // check individual bytes
                         CHECK(result[0] == 'I');
-                        auto const restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
+                        auto const restored = static_cast<uint16_t>((static_cast<uint8_t>(result[1]) * 256) + static_cast<uint8_t>(result[2]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -655,7 +655,7 @@ TEST_CASE("UBJSON")
 
                         // check individual bytes
                         CHECK(result[0] == 'I');
-                        auto const restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
+                        auto const restored = static_cast<uint16_t>((static_cast<uint8_t>(result[1]) * 256) + static_cast<uint8_t>(result[2]));
                         CHECK(restored == i);
 
                         // roundtrip

tests/src/unit-udt_macro.cpp

@@ -442,7 +442,7 @@ NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(person_without_default_constru
 
 } // namespace persons
 
-TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE", T,
+TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE", T, // NOLINT(readability-math-missing-parentheses)
                    persons::person_with_private_data,
                    persons::person_without_private_data_1,
                    persons::person_without_private_data_2)
@@ -464,11 +464,15 @@ TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRU
         // check exception in case of missing field
         json j = json(p1);
         j.erase("age");
+#if defined(JSON_HAS_CPP_17)
+        CHECK_THROWS_WITH_AS(j.get<T>(), "[json.exception.out_of_range.403] key not found (key is an rvalue and cannot be shown)", json::out_of_range);
+#else
         CHECK_THROWS_WITH_AS(j.get<T>(), "[json.exception.out_of_range.403] key 'age' not found", json::out_of_range);
+#endif
     }
 }
 
-TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE and NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE", T,
+TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE and NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE", T, // NOLINT(readability-math-missing-parentheses)
                    persons::derived_person_with_private_data,
                    persons::derived_person_without_private_data_1,
                    persons::derived_person_without_private_data_2)
@@ -494,7 +498,33 @@ TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_DERIVED_TY
     }
 }
 
-TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT", T,
+TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE and NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE", T, // NOLINT(readability-math-missing-parentheses)
+                   persons::derived_person_with_private_data,
+                   persons::derived_person_without_private_data_1,
+                   persons::derived_person_without_private_data_2)
+{
+    SECTION("person")
+    {
+        // serialization
+        T p1("Erik", 1, {{"haircuts", 2}}, "red");
+        CHECK(json(p1).dump() == "{\"age\":1,\"hair_color\":\"red\",\"metadata\":{\"haircuts\":2},\"name\":\"Erik\"}");
+
+        // deserialization
+        auto p2 = json(p1).get<T>();
+        CHECK(p2 == p1);
+
+        // roundtrip
+        CHECK(T(json(p1)) == p1);
+        CHECK(json(T(json(p1))) == json(p1));
+
+        // check exception in case of missing field
+        json j = json(p1);
+        j.erase("age");
+        CHECK_THROWS_WITH_AS(j.get<T>(), "[json.exception.out_of_range.403] key 'age' not found", json::out_of_range);
+    }
+}
+
+TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT", T, // NOLINT(readability-math-missing-parentheses)
                    persons::person_with_private_data_2,
                    persons::person_without_private_data_3)
 {
@@ -528,7 +558,7 @@ TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRU
     }
 }
 
-TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT and NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT", T,
+TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT and NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT", T, // NOLINT(readability-math-missing-parentheses)
                    persons::derived_person_with_private_data_2,
                    persons::derived_person_without_private_data_3)
 {
@@ -564,7 +594,7 @@ TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_DERIVED_TY
     }
 }
 
-TEST_CASE_TEMPLATE("Serialization/deserialization of classes with 26 public/private member variables via NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE", T,
+TEST_CASE_TEMPLATE("Serialization/deserialization of classes with 26 public/private member variables via NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE", T, // NOLINT(readability-math-missing-parentheses)
                    persons::person_with_private_alphabet,
                    persons::person_with_public_alphabet)
 {
@@ -636,7 +666,7 @@ TEST_CASE_TEMPLATE("Serialization/deserialization of classes with 26 public/priv
     }
 }
 
-TEST_CASE_TEMPLATE("Serialization of non-default-constructible classes via NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE", T,
+TEST_CASE_TEMPLATE("Serialization of non-default-constructible classes via NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE", T, // NOLINT(readability-math-missing-parentheses)
                    persons::person_without_default_constructor_1,
                    persons::person_without_default_constructor_2)
 {

tests/src/unit-unicode1.cpp

@@ -155,7 +155,7 @@ TEST_CASE("Unicode (1/5)" * doctest::skip())
 
     SECTION("read all unicode characters")
     {
-        // read a file with all unicode characters stored as single-character
+        // 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;