Merge ci/tiers

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

.github/CONTRIBUTING.md

@@ -154,6 +154,15 @@ and each page's title (H1) and declaration by
 [`docs/docset/generate_docset.py`](https://github.com/nlohmann/json/blob/develop/docs/docset/generate_docset.py);
 `make build` reports API pages that cannot be classified.
 
+A pull request that changes only the documentation, Markdown files, GitHub metadata, or license files skips the
+compiler workflows (Ubuntu, macOS, Windows); the documentation and license checks still run. See
+[`tools/check_path_filters`](https://github.com/nlohmann/json/tree/develop/tools/check_path_filters) for the list of
+skipped files and what to do when a compiler job starts reading one of them.
+
+Most compiler jobs run only once a maintainer adds the label "🚀 ready to merge" to a pull request; until then, a
+smaller set of jobs runs on every push. See
+[How CI runs](https://json.nlohmann.me/community/quality_assurance/#how-ci-runs) for the sets and when they run.
+
 ### Amalgamate the source code
 
 The single-header files

.github/workflows/macos.yml

@@ -7,25 +7,60 @@ on:
       - master
       - release/*
   pull_request:
+    # labeled: the "🚀 ready to merge" label starts the full set (see below)
+    types: [opened, synchronize, reopened, labeled]
+    # Skip pull requests that change only files no job here reads. The list is checked by
+    # tools/check_path_filters/check_path_filters.py (repository_checks.yml); change both together.
+    paths:
+      - '**'
+      - '!docs/**'
+      - '!**.md'
+      - '!.github/*'
+      - '!.github/ISSUE_TEMPLATE/**'
+      - '!.github/external_ci/**'
+      - '!.github/workflows/**'
+      - '!.reuse/**'
+      - '!LICENSES/**'
+      - '!CITATION.cff'
+      - '!REUSE.toml'
+      # read by tools/check_build_options in the ci_meson_install job (ubuntu.yml)
+      - 'docs/mkdocs/docs/integration/package_managers.md'
+      # built by the swiftpm job (macos.yml)
+      - 'docs/mkdocs/docs/integration/swift/**'
+      - '.github/workflows/macos.yml'
   workflow_dispatch:
 
+# A run triggered by any other label gets a group of its own, so it does not
+# cancel the run of the last push; its jobs are skipped.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
+  group: ${{ github.workflow }}-${{ github.event_name == 'schedule' && 'nightly' || github.ref || github.run_id }}${{ github.event.action == 'labeled' && github.event.label.name != '🚀 ready to merge' && format('-{0}', github.run_id) || '' }}
   cancel-in-progress: true
 
 permissions:
   contents: read
 
+
+# The jobs are split into a PR set and a full set like in ubuntu.yml (see "How
+# CI runs" in docs/mkdocs/docs/community/quality_assurance.md): the PR set runs
+# on every push; the full set after the PR set passed, on pushes and on pull
+# requests with the "🚀 ready to merge" label. tools/ci_jobs checks that every
+# job belongs to exactly one set.
+
 jobs:
+  ###########################################################################
+  # PR set
+  ###########################################################################
+
   macos-15:
+    if: &pr_set ${{ github.event_name != 'schedule' && (github.event.action != 'labeled' || github.event.label.name == '🚀 ready to merge') }}
     runs-on: macos-15 # https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
     strategy:
       matrix:
-        xcode: ['16.0', '16.1', '16.2', '16.3', '16.4', '26.0.1', '26.1.1', '26.2', '26.3']
+        xcode: ['16.0', '16.4', '26.3']
     env:
       DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
 
-    steps:
+    steps: &xcode_steps
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
@@ -37,10 +72,11 @@ jobs:
         run: cd build ; ctest -j 10 --output-on-failure
 
   macos-26:
+    if: *pr_set
     runs-on: macos-26 # https://github.com/actions/runner-images/blob/main/images/macos/macos-26-arm64-Readme.md
     strategy:
       matrix:
-        xcode: ['26.4.1', '26.5', '26.6']
+        xcode: ['26.6']
     env:
       DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
 
@@ -56,12 +92,13 @@ jobs:
         run: cd build ; ctest -j 10 --output-on-failure
 
   xcode_standards:
+    if: *pr_set
     runs-on: macos-latest
     strategy:
       matrix:
-        standard: [11, 14, 17, 20, 23, 26]
+        standard: [14]
 
-    steps:
+    steps: &xcode_standards_steps
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
@@ -73,6 +110,7 @@ jobs:
         run: cd build ; ctest -j 10 --output-on-failure
 
   swiftpm:
+    if: *pr_set
     runs-on: macos-15
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -106,3 +144,42 @@ jobs:
           EOF
           cd /tmp/json-swiftpm-consumer
           swift build
+
+
+  ###########################################################################
+  # full set: starts after the PR set passed
+  ###########################################################################
+
+  macos-15_full:
+    needs: &pr_set_jobs [macos-15, macos-26, xcode_standards, swiftpm]
+    if: &full_set ${{ github.event_name == 'push' || github.event_name == 'workflow_dispatch' || contains(github.event.pull_request.labels.*.name, '🚀 ready to merge') }}
+    runs-on: macos-15 # https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
+    strategy:
+      matrix:
+        xcode: ['16.1', '16.2', '16.3', '26.0.1', '26.1.1', '26.2']
+    env:
+      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
+
+    steps: *xcode_steps
+
+  macos-26_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: macos-26 # https://github.com/actions/runner-images/blob/main/images/macos/macos-26-arm64-Readme.md
+    strategy:
+      matrix:
+        xcode: ['26.4.1', '26.5']
+    env:
+      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
+
+    steps: *xcode_steps
+
+  xcode_standards_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: macos-latest
+    strategy:
+      matrix:
+        standard: [11, 17, 20, 23, 26]
+
+    steps: *xcode_standards_steps

.github/workflows/repository_checks.yml

@@ -0,0 +1,83 @@
+name: Repository checks
+
+# Checks that concern files the compiler workflows (ubuntu.yml, macos.yml,
+# windows.yml) skip with their path filter: the documentation, the license
+# information, and the CI configuration itself. This workflow has no path filter.
+on:
+  push:
+    branches:
+      - develop
+      - master
+      - release/*
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  check_ci_configuration:
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
+        with:
+          egress-policy: audit
+
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Check the path filters of the compiler workflows
+        run: python3 tools/check_path_filters/check_path_filters.py
+      - name: Check the job sets of the compiler workflows and their documentation
+        run: |
+          python3 -m venv venv
+          venv/bin/pip install --quiet -r tools/ci_jobs/requirements.txt
+          venv/bin/python tools/ci_jobs/ci_jobs.py
+
+  ci_reuse_compliance:
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
+        with:
+          egress-policy: audit
+
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ci_reuse_compliance
+
+  ci_test_documentation:
+    runs-on: ubuntu-26.04
+    strategy:
+      matrix:
+        target: [ci_test_examples, ci_test_build_documentation, ci_test_documentation_mermaid]
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
+        with:
+          egress-policy: audit
+
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+          # the git-revision-date-localized plugin needs the history; a shallow clone makes the strict build fail
+          fetch-depth: ${{ matrix.target == 'ci_test_build_documentation' && '0' || '1' }}
+      - uses: actions/setup-node@949feb2413d6458794dcd2491c4babbbce0c15c1 # v7.1.0
+        if: matrix.target == 'ci_test_documentation_mermaid'
+        with:
+          node-version: 24
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ${{ matrix.target }}

.github/workflows/ubuntu.yml

@@ -7,17 +7,62 @@ on:
       - master
       - release/*
   pull_request:
+    # labeled: the "🚀 ready to merge" label starts the full set (see below)
+    types: [opened, synchronize, reopened, labeled]
+    # Skip pull requests that change only files no job here reads. The list is checked by
+    # tools/check_path_filters/check_path_filters.py (repository_checks.yml); change both together.
+    paths:
+      - '**'
+      - '!docs/**'
+      - '!**.md'
+      - '!.github/*'
+      - '!.github/ISSUE_TEMPLATE/**'
+      - '!.github/external_ci/**'
+      - '!.github/workflows/**'
+      - '!.reuse/**'
+      - '!LICENSES/**'
+      - '!CITATION.cff'
+      - '!REUSE.toml'
+      # read by tools/check_build_options in the ci_meson_install job (ubuntu.yml)
+      - 'docs/mkdocs/docs/integration/package_managers.md'
+      # built by the swiftpm job (macos.yml)
+      - 'docs/mkdocs/docs/integration/swift/**'
+      - '.github/workflows/ubuntu.yml'
+  schedule:
+    # the nightly set (see below), on develop
+    - cron: '0 2 * * *'
   workflow_dispatch:
 
 permissions:
   contents: read
 
+# A run triggered by any other label gets a group of its own, so it does not
+# cancel the run of the last push; its jobs are skipped.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
+  group: ${{ github.workflow }}-${{ github.event_name == 'schedule' && 'nightly' || github.ref || github.run_id }}${{ github.event.action == 'labeled' && github.event.label.name != '🚀 ready to merge' && format('-{0}', github.run_id) || '' }}
   cancel-in-progress: true
 
+# The jobs are split into three sets (see "How CI runs" in
+# docs/mkdocs/docs/community/quality_assurance.md):
+#
+# - PR set: every pull request push and every push; chosen because these jobs
+#   caught 92 % of the failing commits in Sep/Oct 2026.
+# - full set: after the PR set passed, on pushes and on pull requests with the
+#   "🚀 ready to merge" label; every remaining compiler, version and standard.
+# - nightly set: slow tools and rare compilers, nightly on develop, on pushes
+#   to master and release/*, and when started by hand.
+#
+# A matrix whose entries belong to different sets is split into one job per
+# set; the jobs share their steps through YAML anchors. tools/ci_jobs checks
+# that every job belongs to exactly one set.
+
 jobs:
+  ###########################################################################
+  # PR set
+  ###########################################################################
+
   ci_test_gcc:
+    if: &pr_set ${{ github.event_name != 'schedule' && (github.event.action != 'labeled' || github.event.label.name == '🚀 ready to merge') }}
     runs-on: ubuntu-latest
     container: gcc:latest
     steps:
@@ -32,6 +77,7 @@ jobs:
         run: cmake --build build --target ci_test_gcc
 
   ci_meson_install:
+    if: *pr_set
     runs-on: ubuntu-26.04
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -76,7 +122,342 @@ jobs:
           cmake -S tests/cmake_import/project -B build-import-split -DCMAKE_PREFIX_PATH=${{ github.workspace }}/install-split
           cmake --build build-import-split
 
+  ci_static_analysis_ubuntu:
+    if: *pr_set
+    runs-on: ubuntu-26.04
+    strategy:
+      matrix:
+        target: [ci_cpplint]
+    steps: &static_analysis_ubuntu_steps
+      - name: Harden Runner
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
+        with:
+          egress-policy: audit
+
+      - name: Install Valgrind
+        if: matrix.target == 'ci_test_valgrind'
+        run: sudo apt-get update ; sudo apt-get install -y valgrind
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ${{ matrix.target }}
+
+  ci_static_analysis_clang:
+    if: *pr_set
+    runs-on: ubuntu-latest
+    container: silkeh/clang:22
+    strategy:
+      matrix:
+        target: [ci_test_clang, ci_clang_tidy, ci_test_clang_sanitizer, ci_single_binaries]
+    steps: &static_analysis_clang_steps
+      - name: Install git, clang-tools, iwyu (ci_single_binaries), and unzip
+        run: apt-get update ; apt-get install -y git clang-tools iwyu unzip
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ${{ matrix.target }}
+
+  ci_cmake_options:
+    if: *pr_set
+    runs-on: ubuntu-latest
+    container: ubuntu:24.04
+    strategy:
+      matrix:
+        target: [ci_test_diagnostics, ci_test_diagnostic_positions, ci_test_noexceptions, ci_test_noglobaludls]
+    steps: &cmake_options_steps
+      - name: Install build-essential
+        run: apt-get update ; apt-get install -y build-essential unzip wget git
+      # the CMake 3.5.0 release binary that ci_cmake_flags downloads links
+      # against libidn.so.11, which Ubuntu 24.04 no longer ships
+      - name: Install libidn11 for CMake 3.5.0
+        if: matrix.target == 'ci_cmake_flags'
+        run: |
+          wget -q http://archive.ubuntu.com/ubuntu/pool/main/libi/libidn/libidn11_1.33-2.2ubuntu2_amd64.deb
+          dpkg -i libidn11_1.33-2.2ubuntu2_amd64.deb
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ${{ matrix.target }}
+
+  ci_test_compilers_gcc_old:
+    if: *pr_set
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        compiler: ['4.8']
+    # official gcc:4.8/4.9/5/6 images fail to check out code (too old for
+    # actions/checkout); install the old compilers on top of official ubuntu:20.04
+    # instead, mirroring what the (now retired) custom json-ci image did.
+    container: ubuntu:20.04
+    steps: &compilers_gcc_old_steps
+      - name: Install g++-${{ matrix.compiler }}
+        run: |
+          export DEBIAN_FRONTEND=noninteractive
+          apt-get update
+          apt-get install -y --no-install-recommends software-properties-common ca-certificates gnupg make git
+          # add-apt-repository resolves the PPA through the Launchpad API,
+          # which intermittently times out or fails the team lookup (the plain
+          # "deb ..." sources below never hit Launchpad and never flake).
+          # Retry with backoff so a transient Launchpad blip does not fail CI.
+          for attempt in 1 2 3 4 5; do
+            add-apt-repository -y ppa:ubuntu-toolchain-r/test && break
+            echo "::warning::add-apt-repository ppa:ubuntu-toolchain-r/test failed (attempt ${attempt}/5); retrying"
+            sleep $((attempt * 10))
+          done
+          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ bionic main"
+          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ bionic universe"
+          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial main"
+          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial universe"
+          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial-updates main"
+          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial-updates universe"
+          apt-get update
+          apt-get install -y --no-install-recommends g++-${{ matrix.compiler }}
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - 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_clang:
+    if: *pr_set
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        compiler: ['3.4']
+    container: silkeh/clang:${{ matrix.compiler }}
+    steps: &compilers_clang_steps
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - name: Disable filesystem support (std::filesystem is unusable) for clang 7 / 8 / 9 / 10
+        run: echo "JSON_FORCED_GLOBAL_COMPILE_OPTIONS=-DJSON_HAS_FILESYSTEM=0;-DJSON_HAS_EXPERIMENTAL_FILESYSTEM=0" >> "$GITHUB_ENV"
+        if: ${{ matrix.compiler == '7' || matrix.compiler == '8' || matrix.compiler == '9' || matrix.compiler == '10' }}
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ci_test_compiler_default
+
+  ci_test_standards_gcc:
+    if: *pr_set
+    runs-on: ubuntu-latest
+    container: gcc:latest
+    strategy:
+      matrix:
+        standard: [26]
+    steps: &standards_gcc_steps
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ci_test_gcc_cxx${{ matrix.standard }}
+
+  ci_test_standards_clang:
+    if: *pr_set
+    runs-on: ubuntu-latest
+    container: silkeh/clang:latest
+    strategy:
+      matrix:
+        standard: [26]
+        stdlib: [libcxx]
+    steps: &standards_clang_steps
+      - name: Install git and unzip
+        run: apt-get update ; apt-get install -y git unzip
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - 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: ${{ matrix.stdlib == 'libstdcxx' }}
+
+  ci_emscripten:
+    if: *pr_set
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
+        with:
+          egress-policy: audit
+
+      - name: Install emscripten
+        uses: mymindstorm/setup-emsdk@4528d102f7230f0e7b276855c01ea1159be0e984 # v16
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - name: Run CMake
+        run: cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=$EMSDK/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -GNinja
+      - name: Build
+        run: cmake --build build
+
+  ###########################################################################
+  # full set: starts after the PR set passed
+  ###########################################################################
+
+  ci_static_analysis_ubuntu_full:
+    needs: &pr_set_jobs [ci_test_gcc, ci_meson_install, ci_static_analysis_ubuntu, ci_static_analysis_clang, ci_cmake_options, ci_test_compilers_gcc_old, ci_test_compilers_clang, ci_test_standards_gcc, ci_test_standards_clang, ci_emscripten]
+    if: &full_set ${{ github.event_name == 'push' || github.event_name == 'workflow_dispatch' || contains(github.event.pull_request.labels.*.name, '🚀 ready to merge') }}
+    runs-on: ubuntu-26.04
+    strategy:
+      matrix:
+        target: [ci_test_single_header, ci_cppcheck, ci_reproducible_tests, ci_non_git_tests, ci_offline_testdata]
+    steps: *static_analysis_ubuntu_steps
+
+  ci_static_analysis_clang_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: ubuntu-latest
+    container: silkeh/clang:22
+    strategy:
+      matrix:
+        target: [ci_clang_analyze]
+    steps: *static_analysis_clang_steps
+
+  ci_cmake_options_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: ubuntu-latest
+    container: ubuntu:24.04
+    strategy:
+      matrix:
+        target: [ci_cmake_flags, ci_test_noimplicitconversions, ci_test_legacycomparison, ci_test_disableenumserialization, ci_test_disabletuplereferenceconversion, ci_test_skiplibraryversioncheck, ci_test_simdutf, ci_test_strict_nul_handling, ci_test_delete_deprecated_functions, ci_test_no_thread_local]
+    steps: *cmake_options_steps
+
+  ci_test_compilers_gcc_old_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        compiler: ['4.9', '5', '6']
+    container: ubuntu:20.04
+    steps: *compilers_gcc_old_steps
+
+  ci_test_compilers_gcc_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        # older GCC docker images (4, 5, 6) fail to check out code
+        compiler: ['7', '8', '9', '10', '11', '12', '13', '14', '15', '16', 'latest']
+    container: gcc:${{ matrix.compiler }}
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ci_test_compiler_default
+
+  ci_test_compilers_clang_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    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', '16', '17', '18', '19', '20', '21', '22', 'latest']
+    container: silkeh/clang:${{ matrix.compiler }}
+    steps: *compilers_clang_steps
+
+  ci_test_standards_gcc_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: ubuntu-latest
+    container: gcc:latest
+    strategy:
+      matrix:
+        standard: [11, 14, 17, 20, 23]
+    steps: *standards_gcc_steps
+
+  ci_test_standards_clang_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: ubuntu-latest
+    container: silkeh/clang:latest
+    strategy:
+      matrix:
+        standard: [11, 14, 17, 20, 23, 26]
+        stdlib: [libcxx, libstdcxx]
+        exclude:
+          # in the PR set
+          - standard: 26
+            stdlib: libcxx
+    steps: *standards_clang_steps
+
+  ci_module_cpp20:
+    needs: *pr_set_jobs
+    if: *full_set
+    strategy:
+      matrix:
+        container: ['gcc:latest', 'silkeh/clang:latest']
+    runs-on: ubuntu-latest
+    container: ${{ matrix.container }}
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      # The module test uses `import std;`, which needs CMake's experimental
+      # import-std support. Its opt-in token is CMake-version-specific, so pin
+      # CMake to the version whose token is set in tests/module_cpp20/CMakeLists.txt.
+      - name: Get pinned CMake and ninja
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
+        with:
+          cmakeVersion: 4.3.4
+      # Clang: the std library module is provided by libc++ (the image's libstdc++
+      # ships none), and the image's libc++ module manifest has a broken relative
+      # path — repoint it at the real module sources.
+      - name: Use libc++ and fix its module manifest path (Clang)
+        if: matrix.container == 'silkeh/clang:latest'
+        run: |
+          echo "CXXFLAGS=-stdlib=libc++" >> "$GITHUB_ENV"
+          mkdir -p /usr/lib/share && ln -sf /usr/lib/llvm-*/share/libc++ /usr/lib/share/libc++
+      - name: Run CMake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: Build
+        run: cmake --build build --target ci_module_cpp20
+
+  ###########################################################################
+  # nightly set
+  ###########################################################################
+
   ci_infer:
+    if: &nightly_set ${{ github.event_name == 'schedule' || github.event_name == 'workflow_dispatch' || (github.event_name == 'push' && github.ref != 'refs/heads/develop') }}
     runs-on: ubuntu-26.04
     steps:
       - name: Harden Runner
@@ -105,76 +486,16 @@ jobs:
           path: ${{ github.workspace }}/build/build_infer/infer-out/report.txt
           if-no-files-found: ignore
 
-  ci_static_analysis_ubuntu:
+  ci_static_analysis_ubuntu_nightly:
+    if: *nightly_set
     runs-on: ubuntu-26.04
     strategy:
       matrix:
-        target: [ci_test_single_header, ci_cppcheck, ci_cpplint, ci_reproducible_tests, ci_non_git_tests, ci_offline_testdata, ci_reuse_compliance, ci_test_valgrind]
+        target: [ci_test_valgrind]
-    steps:
+    steps: *static_analysis_ubuntu_steps
-      - name: Harden Runner
-        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
-        with:
-          egress-policy: audit
-
-      - name: Install Valgrind
-        if: matrix.target == 'ci_test_valgrind'
-        run: sudo apt-get update ; sudo apt-get install -y valgrind
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-      - name: Run CMake
-        run: cmake -S . -B build -DJSON_CI=On
-      - name: Build
-        run: cmake --build build --target ${{ matrix.target }}
-
-  ci_static_analysis_clang:
-    runs-on: ubuntu-latest
-    container: silkeh/clang:22
-    strategy:
-      matrix:
-        target: [ci_test_clang, ci_clang_tidy, ci_test_clang_sanitizer, ci_clang_analyze, ci_single_binaries]
-    steps:
-      - name: Install git, clang-tools, iwyu (ci_single_binaries), and unzip
-        run: apt-get update ; apt-get install -y git clang-tools iwyu unzip
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-      - name: Run CMake
-        run: cmake -S . -B build -DJSON_CI=On
-      - name: Build
-        run: cmake --build build --target ${{ matrix.target }}
-
-  ci_cmake_options:
-    runs-on: ubuntu-latest
-    container: ubuntu:24.04
-    strategy:
-      matrix:
-        target: [ci_cmake_flags, ci_test_diagnostics, ci_test_diagnostic_positions, ci_test_noexceptions, ci_test_noimplicitconversions, ci_test_legacycomparison, ci_test_noglobaludls, ci_test_disableenumserialization, ci_test_disabletuplereferenceconversion, ci_test_skiplibraryversioncheck, ci_test_simdutf, ci_test_strict_nul_handling, ci_test_delete_deprecated_functions, ci_test_no_thread_local]
-    steps:
-      - name: Install build-essential
-        run: apt-get update ; apt-get install -y build-essential unzip wget git
-      # the CMake 3.5.0 release binary that ci_cmake_flags downloads links
-      # against libidn.so.11, which Ubuntu 24.04 no longer ships
-      - name: Install libidn11 for CMake 3.5.0
-        if: matrix.target == 'ci_cmake_flags'
-        run: |
-          wget -q http://archive.ubuntu.com/ubuntu/pool/main/libi/libidn/libidn11_1.33-2.2ubuntu2_amd64.deb
-          dpkg -i libidn11_1.33-2.2ubuntu2_amd64.deb
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-      - name: Run CMake
-        run: cmake -S . -B build -DJSON_CI=On
-      - name: Build
-        run: cmake --build build --target ${{ matrix.target }}
 
   ci_test_coverage:
+    if: *nightly_set
     runs-on: ubuntu-26.04
     steps:
       - name: Harden Runner
@@ -208,128 +529,8 @@ jobs:
           path-to-lcov: ${{ github.workspace }}/build/json.info.filtered.noexcept
           fail-on-error: false
 
-  ci_test_compilers_gcc_old:
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        compiler: ['4.8', '4.9', '5', '6']
-    # official gcc:4.8/4.9/5/6 images fail to check out code (too old for
-    # actions/checkout); install the old compilers on top of official ubuntu:20.04
-    # instead, mirroring what the (now retired) custom json-ci image did.
-    container: ubuntu:20.04
-    steps:
-      - name: Install g++-${{ matrix.compiler }}
-        run: |
-          export DEBIAN_FRONTEND=noninteractive
-          apt-get update
-          apt-get install -y --no-install-recommends software-properties-common ca-certificates gnupg make git
-          # add-apt-repository resolves the PPA through the Launchpad API,
-          # which intermittently times out or fails the team lookup (the plain
-          # "deb ..." sources below never hit Launchpad and never flake).
-          # Retry with backoff so a transient Launchpad blip does not fail CI.
-          for attempt in 1 2 3 4 5; do
-            add-apt-repository -y ppa:ubuntu-toolchain-r/test && break
-            echo "::warning::add-apt-repository ppa:ubuntu-toolchain-r/test failed (attempt ${attempt}/5); retrying"
-            sleep $((attempt * 10))
-          done
-          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ bionic main"
-          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ bionic universe"
-          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial main"
-          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial universe"
-          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial-updates main"
-          apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial-updates universe"
-          apt-get update
-          apt-get install -y --no-install-recommends g++-${{ matrix.compiler }}
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-      - 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:
-        # older GCC docker images (4, 5, 6) fail to check out code
-        compiler: ['7', '8', '9', '10', '11', '12', '13', '14', '15', '16', 'latest']
-    container: gcc:${{ matrix.compiler }}
-    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-      - name: Run CMake
-        run: cmake -S . -B build -DJSON_CI=On
-      - name: Build
-        run: cmake --build build --target ci_test_compiler_default
-
-  ci_test_compilers_clang:
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        compiler: ['3.4', '3.5', '3.6', '3.7', '3.8', '3.9', '4', '5', '6', '7', '8', '9', '10', '11', '12', '13', '14', '15-bullseye', '16', '17', '18', '19', '20', '21', '22', 'latest']
-    container: silkeh/clang:${{ matrix.compiler }}
-    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-      - name: Disable filesystem support (std::filesystem is unusable) 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: ${{ matrix.compiler == '7' || matrix.compiler == '8' || matrix.compiler == '9' || matrix.compiler == '10' }}
-      - name: Run CMake
-        run: cmake -S . -B build -DJSON_CI=On
-      - name: Build
-        run: cmake --build build --target ci_test_compiler_default
-
-  ci_test_standards_gcc:
-    runs-on: ubuntu-latest
-    container: gcc:latest
-    strategy:
-      matrix:
-        standard: [11, 14, 17, 20, 23, 26]
-    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-      - name: Run CMake
-        run: cmake -S . -B build -DJSON_CI=On
-      - name: Build
-        run: cmake --build build --target ci_test_gcc_cxx${{ matrix.standard }}
-
-  ci_test_standards_clang:
-    runs-on: ubuntu-latest
-    container: silkeh/clang:latest
-    strategy:
-      matrix:
-        standard: [11, 14, 17, 20, 23, 26]
-        stdlib: [libcxx, libstdcxx]
-    steps:
-      - name: Install git and unzip
-        run: apt-get update ; apt-get install -y git unzip
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-      - name: Run CMake
-        run: cmake -S . -B build -DJSON_CI=On
-      - 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:
+    if: *nightly_set
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
@@ -352,37 +553,8 @@ jobs:
       - name: Build
         run: cmake --build build --target ci_cuda_example
 
-  ci_module_cpp20:
-    strategy:
-      matrix:
-        container: ['gcc:latest', 'silkeh/clang:latest']
-    runs-on: ubuntu-latest
-    container: ${{ matrix.container }}
-    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      # The module test uses `import std;`, which needs CMake's experimental
-      # import-std support. Its opt-in token is CMake-version-specific, so pin
-      # CMake to the version whose token is set in tests/module_cpp20/CMakeLists.txt.
-      - name: Get pinned CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-        with:
-          cmakeVersion: 4.3.4
-      # Clang: the std library module is provided by libc++ (the image's libstdc++
-      # ships none), and the image's libc++ module manifest has a broken relative
-      # path — repoint it at the real module sources.
-      - name: Use libc++ and fix its module manifest path (Clang)
-        if: matrix.container == 'silkeh/clang:latest'
-        run: |
-          echo "CXXFLAGS=-stdlib=libc++" >> "$GITHUB_ENV"
-          mkdir -p /usr/lib/share && ln -sf /usr/lib/llvm-*/share/libc++ /usr/lib/share/libc++
-      - name: Run CMake
-        run: cmake -S . -B build -DJSON_CI=On
-      - name: Build
-        run: cmake --build build --target ci_module_cpp20
-
   ci_icpc:
+    if: *nightly_set
     runs-on: ubuntu-latest
     # Intel discontinued the classic icc/icpc compiler in oneAPI 2024.0; this is
     # Intel's own last officially published image that still includes it.
@@ -402,6 +574,7 @@ jobs:
         run: cmake --build build --target ci_icpc
 
   ci_icpx:
+    if: *nightly_set
     runs-on: ubuntu-latest
     container: intel/oneapi-hpckit:latest
     steps:
@@ -416,6 +589,7 @@ jobs:
         run: cmake --build build --target ci_icpx
 
   ci_nvhpc:
+    if: *nightly_set
     runs-on: ubuntu-latest
     container: nvcr.io/nvidia/nvhpc:25.5-devel-cuda12.9-ubuntu22.04
     steps:
@@ -429,54 +603,10 @@ jobs:
       - name: Build
         run: cmake --build build --target ci_nvhpc
 
-  ci_emscripten:
-    runs-on: ubuntu-26.04
-    steps:
-      - name: Harden Runner
-        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
-        with:
-          egress-policy: audit
-
-      - name: Install emscripten
-        uses: mymindstorm/setup-emsdk@4528d102f7230f0e7b276855c01ea1159be0e984 # v16
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
-      - name: Run CMake
-        run: cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=$EMSDK/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -GNinja
-      - name: Build
-        run: cmake --build build
-
-  ci_test_documentation:
-    runs-on: ubuntu-26.04
-    strategy:
-      matrix:
-        target: [ci_test_examples, ci_test_build_documentation, ci_test_documentation_mermaid]
-    steps:
-      - name: Harden Runner
-        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
-        with:
-          egress-policy: audit
-
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-          # the git-revision-date-localized plugin needs the history; a shallow clone makes the strict build fail
-          fetch-depth: ${{ matrix.target == 'ci_test_build_documentation' && '0' || '1' }}
-      - uses: actions/setup-node@949feb2413d6458794dcd2491c4babbbce0c15c1 # v7.1.0
-        if: matrix.target == 'ci_test_documentation_mermaid'
-        with:
-          node-version: 24
-      - name: Run CMake
-        run: cmake -S . -B build -DJSON_CI=On
-      - name: Build
-        run: cmake --build build --target ${{ matrix.target }}
-
   # Native Linux ARM64 runner with the latest GCC. The ubuntu-24.04-arm label is
   # only available for public repositories.
   ci_test_arm64:
+    if: *nightly_set
     runs-on: ubuntu-24.04-arm
     container: gcc:latest
     steps:
@@ -491,3 +621,33 @@ jobs:
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
         run: cmake --build build --target ci_test_compiler_default
+
+  # A failure of a scheduled run opens an issue, or comments on the open one.
+  nightly_report:
+    needs: [ci_infer, ci_static_analysis_ubuntu_nightly, ci_test_coverage, ci_cuda_example, ci_icpc, ci_icpx, ci_nvhpc, ci_test_arm64]
+    if: ${{ always() && github.event_name == 'schedule' && contains(needs.*.result, 'failure') }}
+    runs-on: ubuntu-26.04
+    permissions:
+      issues: write
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
+        with:
+          egress-policy: audit
+
+      - name: Open or update the nightly failure issue
+        env:
+          GH_TOKEN: ${{ github.token }}
+          GH_REPO: ${{ github.repository }}
+          RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
+          WORKFLOW: ${{ github.workflow }}
+          SHA: ${{ github.sha }}
+        run: |
+          title="Nightly CI failure (${WORKFLOW})"
+          body="The nightly run of ${WORKFLOW} on ${SHA:0:10} failed: ${RUN_URL}"
+          number=$(gh issue list --state open --search "in:title \"${title}\"" --json number,title --jq "map(select(.title == \"${title}\")) | .[0].number // empty")
+          if [ -n "$number" ]; then
+            gh issue comment "$number" --body "$body"
+          else
+            gh issue create --title "$title" --body "$body"
+          fi

.github/workflows/windows.yml

@@ -7,23 +7,62 @@ on:
       - master
       - release/*
   pull_request:
+    # labeled: the "🚀 ready to merge" label starts the full set (see below)
+    types: [opened, synchronize, reopened, labeled]
+    # Skip pull requests that change only files no job here reads. The list is checked by
+    # tools/check_path_filters/check_path_filters.py (repository_checks.yml); change both together.
+    paths:
+      - '**'
+      - '!docs/**'
+      - '!**.md'
+      - '!.github/*'
+      - '!.github/ISSUE_TEMPLATE/**'
+      - '!.github/external_ci/**'
+      - '!.github/workflows/**'
+      - '!.reuse/**'
+      - '!LICENSES/**'
+      - '!CITATION.cff'
+      - '!REUSE.toml'
+      # read by tools/check_build_options in the ci_meson_install job (ubuntu.yml)
+      - 'docs/mkdocs/docs/integration/package_managers.md'
+      # built by the swiftpm job (macos.yml)
+      - 'docs/mkdocs/docs/integration/swift/**'
+      - '.github/workflows/windows.yml'
+  schedule:
+    # the nightly set (see below), on develop
+    - cron: '0 2 * * *'
   workflow_dispatch:
 
 permissions:
   contents: read
 
+# A run triggered by any other label gets a group of its own, so it does not
+# cancel the run of the last push; its jobs are skipped.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
+  group: ${{ github.workflow }}-${{ github.event_name == 'schedule' && 'nightly' || github.ref || github.run_id }}${{ github.event.action == 'labeled' && github.event.label.name != '🚀 ready to merge' && format('-{0}', github.run_id) || '' }}
   cancel-in-progress: true
 
+
+# The jobs are split into three sets like in ubuntu.yml (see "How CI runs" in
+# docs/mkdocs/docs/community/quality_assurance.md): the PR set runs on every
+# push; the full set after the PR set passed, on pushes and on pull requests
+# with the "🚀 ready to merge" label; the nightly set nightly on develop, on
+# pushes to master and release/*, and when started by hand. tools/ci_jobs
+# checks that every job belongs to exactly one set.
+
 jobs:
+  ###########################################################################
+  # PR set
+  ###########################################################################
+
   mingw:
+    if: &pr_set ${{ github.event_name != 'schedule' && (github.event.action != 'labeled' || github.event.label.name == '🚀 ready to merge') }}
     runs-on: windows-2022
     strategy:
       matrix:
-        architecture: [x64, x86]
+        architecture: [x86]
 
-    steps:
+    steps: &mingw_steps
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
@@ -40,15 +79,26 @@ jobs:
         run: cd build ; ctest -j 10 -C Debug --output-on-failure
 
   msvc:
+    if: *pr_set
     strategy:
       matrix:
-        build_type: [Debug, Release]
+        include:
-        architecture: [Win32, x64]
+          - build_type: Debug
-        std_version: [default, latest]
+            architecture: x64
+            std_version: default
+          - build_type: Release
+            architecture: x64
+            std_version: default
+          - build_type: Debug
+            architecture: Win32
+            std_version: default
+          - build_type: Release
+            architecture: Win32
+            std_version: latest
 
     runs-on: windows-2022
 
-    steps:
+    steps: &msvc_steps
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
@@ -77,15 +127,20 @@ jobs:
   # Visual Studio 2026 (v145 toolset) on the windows-2025 image. The "Visual Studio
   # 18 2026" generator requires CMake 4.2+, so a recent CMake is fetched explicitly.
   msvc-vs2026:
+    if: *pr_set
     strategy:
       matrix:
-        build_type: [Debug, Release]
+        include:
-        architecture: [Win32, x64]
+          - build_type: Debug
-        std_version: [default, latest]
+            architecture: x64
+            std_version: latest
+          - build_type: Release
+            architecture: Win32
+            std_version: default
 
     runs-on: windows-2025
 
-    steps:
+    steps: &msvc_vs2026_steps
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
@@ -117,13 +172,14 @@ jobs:
   # Native ARM64 Windows runner with the MSVC ARM64 toolset. The windows-11-arm
   # label is only available for public repositories.
   msvc-arm64:
+    if: *pr_set
     strategy:
       matrix:
-        build_type: [Debug, Release]
+        build_type: [Debug]
 
     runs-on: windows-11-arm
 
-    steps:
+    steps: &msvc_arm64_steps
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
@@ -141,12 +197,13 @@ jobs:
         run: cd build ; ctest -j 10 -C ${{ matrix.build_type }} --output-on-failure
 
   clang:
+    if: *pr_set
     runs-on: windows-2022
     strategy:
       matrix:
-        version: [11.0.1, 12.0.1, 13.0.1, 14.0.6, 15.0.7, 16.0.6, 18.1.8, 19.1.7, 20.1.8]
+        version: [20.1.8]
 
-    steps:
+    steps: &clang_steps
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
@@ -189,24 +246,8 @@ jobs:
       - name: Test
         run: cd build ; ctest -j 10 -C Debug --output-on-failure
 
-  clang-cl:
-    runs-on: windows-2022
-    strategy:
-      matrix:
-        architecture: [Win32, x64]
-
-    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          persist-credentials: false
-      - name: Run CMake
-        run: cmake -S . -B build -G "Visual Studio 17 2022" -A ${{ matrix.architecture }} -T ClangCL -DJSON_BuildTests=On
-      - name: Build
-        run: cmake --build build --config Debug --parallel 10
-      - name: Test
-        run: cd build ; ctest -j 10 -C Debug --output-on-failure
-
   ci_module_cpp20:
+    if: *pr_set
     runs-on: windows-2022
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -226,3 +267,144 @@ jobs:
       - name: Build
         run: cmake --build build --config Debug --target ci_module_cpp20
         
+
+
+  ###########################################################################
+  # full set: starts after the PR set passed
+  ###########################################################################
+
+  msvc_full:
+    needs: &pr_set_jobs [mingw, msvc, msvc-vs2026, msvc-arm64, clang, ci_module_cpp20]
+    if: &full_set ${{ github.event_name == 'push' || github.event_name == 'workflow_dispatch' || contains(github.event.pull_request.labels.*.name, '🚀 ready to merge') }}
+    strategy:
+      matrix:
+        build_type: [Debug, Release]
+        architecture: [Win32, x64]
+        std_version: [default, latest]
+        exclude:
+          # in the PR set
+          - build_type: Debug
+            architecture: x64
+            std_version: default
+          - build_type: Release
+            architecture: x64
+            std_version: default
+          - build_type: Debug
+            architecture: Win32
+            std_version: default
+          - build_type: Release
+            architecture: Win32
+            std_version: latest
+
+    runs-on: windows-2022
+
+    steps: *msvc_steps
+
+  # Visual Studio 2026 (v145 toolset) on the windows-2025 image. The "Visual Studio
+  # 18 2026" generator requires CMake 4.2+, so a recent CMake is fetched explicitly.
+  msvc-vs2026_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    strategy:
+      matrix:
+        build_type: [Debug, Release]
+        architecture: [Win32, x64]
+        std_version: [default, latest]
+        exclude:
+          # in the PR set
+          - build_type: Debug
+            architecture: x64
+            std_version: latest
+          - build_type: Release
+            architecture: Win32
+            std_version: default
+
+    runs-on: windows-2025
+
+    steps: *msvc_vs2026_steps
+
+  # Native ARM64 Windows runner with the MSVC ARM64 toolset. The windows-11-arm
+  # label is only available for public repositories.
+  msvc-arm64_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    strategy:
+      matrix:
+        build_type: [Release]
+
+    runs-on: windows-11-arm
+
+    steps: *msvc_arm64_steps
+
+  clang_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: windows-2022
+    strategy:
+      matrix:
+        version: [11.0.1, 12.0.1, 13.0.1, 14.0.6, 15.0.7, 16.0.6, 18.1.8, 19.1.7]
+
+    steps: *clang_steps
+
+  clang-cl_full:
+    needs: *pr_set_jobs
+    if: *full_set
+    runs-on: windows-2022
+    strategy:
+      matrix:
+        architecture: [Win32, x64]
+
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Run CMake
+        run: cmake -S . -B build -G "Visual Studio 17 2022" -A ${{ matrix.architecture }} -T ClangCL -DJSON_BuildTests=On
+      - name: Build
+        run: cmake --build build --config Debug --parallel 10
+      - name: Test
+        run: cd build ; ctest -j 10 -C Debug --output-on-failure
+
+
+  ###########################################################################
+  # nightly set
+  ###########################################################################
+
+  mingw_nightly:
+    if: ${{ github.event_name == 'schedule' || github.event_name == 'workflow_dispatch' || (github.event_name == 'push' && github.ref != 'refs/heads/develop') }}
+    runs-on: windows-2022
+    strategy:
+      matrix:
+        architecture: [x64]
+
+    steps: *mingw_steps
+
+  # A failure of a scheduled run opens an issue, or comments on the open one.
+  nightly_report:
+    needs: [mingw_nightly]
+    if: ${{ always() && github.event_name == 'schedule' && contains(needs.*.result, 'failure') }}
+    runs-on: ubuntu-26.04
+    permissions:
+      issues: write
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
+        with:
+          egress-policy: audit
+
+      - name: Open or update the nightly failure issue
+        env:
+          GH_TOKEN: ${{ github.token }}
+          GH_REPO: ${{ github.repository }}
+          RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
+          WORKFLOW: ${{ github.workflow }}
+          SHA: ${{ github.sha }}
+        run: |
+          title="Nightly CI failure (${WORKFLOW})"
+          body="The nightly run of ${WORKFLOW} on ${SHA:0:10} failed: ${RUN_URL}"
+          number=$(gh issue list --state open --search "in:title \"${title}\"" --json number,title --jq "map(select(.title == \"${title}\")) | .[0].number // empty")
+          if [ -n "$number" ]; then
+            gh issue comment "$number" --body "$body"
+          else
+            gh issue create --title "$title" --body "$body"
+          fi

docs/mkdocs/docs/community/quality_assurance.md

@@ -13,6 +13,80 @@ describe each of them.
 
 <p class="nj-caption" markdown>The checks grouped by the stage at which they run, from push or pull request through the merge into develop to a release. The badge on each card says whether the check runs on every push or PR, on a schedule, or continuously.</p>
 
+## How CI runs
+
+Not every job runs for every change. The compiler jobs on Ubuntu, macOS, and Windows are split into three sets, so a
+pull request gets fast feedback and the long jobs run when they matter:
+
+| Set         | When it runs                                                                                                      | What it contains                                                                                                                                                                       |
+|-------------|-------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| PR set      | every push to a pull request, and every push to `develop`, `master`, and `release/*`                              | GCC and Clang with all warnings, Clang-Tidy, sanitizers, IWYU, cpplint, the oldest and newest GCC and Clang, common CMake options, Meson, Emscripten, four Visual Studio 2022 and two Visual Studio 2026 configurations, MinGW, Clang on Windows, ARM64 Windows, five Xcode versions, Swift Package Manager; with the checks that always run, they would have caught at least 92 % of the failing commits of September and October 2026 |
+| full set    | after the PR set passed: on pull requests with the label :rocket: ready to merge, and on every push                | every other compiler, version, C++ standard, and CMake option, the Clang Static Analyzer, Cppcheck, and the C++20 module tests                                                         |
+| nightly set | every night on `develop`, on every push to `master` and `release/*`, and when started by hand                      | Infer, Valgrind, coverage, the Intel and NVIDIA compilers, CUDA, ARM64 Linux, and 64-bit MinGW; a failure opens an issue                                                                                    |
+
+The documentation and license checks and the amalgamation check run on every push and pull request; AppVeyor (Visual
+Studio 2015, 2017, and 2019) has its own schedule. A pull request that changes only the documentation, Markdown files, GitHub metadata, or license files
+skips the compiler workflows (see [`tools/check_path_filters`](https://github.com/nlohmann/json/tree/develop/tools/check_path_filters)).
+
+A maintainer adds the label :rocket: ready to merge when a pull request is ready; the full set then runs, and again on
+every later push to that pull request. A pull request is merged only when the full set passed.
+
+??? abstract "Jobs of the compiler workflows and their sets"
+
+    The table is generated by [`tools/ci_jobs`](https://github.com/nlohmann/json/tree/develop/tools/ci_jobs), which
+    also checks in CI that it is up to date and that every job belongs to exactly one set.
+
+    <!-- ci_jobs: begin -->
+    | Set | Workflow | Job | Configurations |
+    |-----|----------|-----|----------------|
+    | PR set | macos.yml | `macos-15` | 16.0; 16.4; 26.3 |
+    | PR set | macos.yml | `macos-26` | 26.6 |
+    | PR set | macos.yml | `xcode_standards` | 14 |
+    | PR set | macos.yml | `swiftpm` | - |
+    | PR set | ubuntu.yml | `ci_test_gcc` | - |
+    | PR set | ubuntu.yml | `ci_meson_install` | - |
+    | PR set | ubuntu.yml | `ci_static_analysis_ubuntu` | ci_cpplint |
+    | PR set | ubuntu.yml | `ci_static_analysis_clang` | ci_test_clang; ci_clang_tidy; ci_test_clang_sanitizer; ci_single_binaries |
+    | PR set | ubuntu.yml | `ci_cmake_options` | ci_test_diagnostics; ci_test_diagnostic_positions; ci_test_noexceptions; ci_test_noglobaludls |
+    | PR set | ubuntu.yml | `ci_test_compilers_gcc_old` | 4.8 |
+    | PR set | ubuntu.yml | `ci_test_compilers_clang` | 3.4 |
+    | PR set | ubuntu.yml | `ci_test_standards_gcc` | 26 |
+    | PR set | ubuntu.yml | `ci_test_standards_clang` | 26, libcxx |
+    | PR set | ubuntu.yml | `ci_emscripten` | - |
+    | PR set | windows.yml | `mingw` | x86 |
+    | PR set | windows.yml | `msvc` | Debug, x64, default; Release, x64, default; Debug, Win32, default; Release, Win32, latest |
+    | PR set | windows.yml | `msvc-vs2026` | Debug, x64, latest; Release, Win32, default |
+    | PR set | windows.yml | `msvc-arm64` | Debug |
+    | PR set | windows.yml | `clang` | 20.1.8 |
+    | PR set | windows.yml | `ci_module_cpp20` | - |
+    | full set | macos.yml | `macos-15_full` | 16.1; 16.2; 16.3; 26.0.1; 26.1.1; 26.2 |
+    | full set | macos.yml | `macos-26_full` | 26.4.1; 26.5 |
+    | full set | macos.yml | `xcode_standards_full` | 11; 17; 20; 23; 26 |
+    | full set | ubuntu.yml | `ci_static_analysis_ubuntu_full` | ci_test_single_header; ci_cppcheck; ci_reproducible_tests; ci_non_git_tests; ci_offline_testdata |
+    | full set | ubuntu.yml | `ci_static_analysis_clang_full` | ci_clang_analyze |
+    | full set | ubuntu.yml | `ci_cmake_options_full` | ci_cmake_flags; ci_test_noimplicitconversions; ci_test_legacycomparison; ci_test_disableenumserialization; ci_test_disabletuplereferenceconversion; ci_test_skiplibraryversioncheck; ci_test_simdutf; ci_test_strict_nul_handling; ci_test_delete_deprecated_functions; ci_test_no_thread_local |
+    | full set | ubuntu.yml | `ci_test_compilers_gcc_old_full` | 4.9; 5; 6 |
+    | full set | ubuntu.yml | `ci_test_compilers_gcc_full` | 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; latest |
+    | full set | ubuntu.yml | `ci_test_compilers_clang_full` | 3.5; 3.6; 3.7; 3.8; 3.9; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15-bullseye; 16; 17; 18; 19; 20; 21; 22; latest |
+    | full set | ubuntu.yml | `ci_test_standards_gcc_full` | 11; 14; 17; 20; 23 |
+    | full set | ubuntu.yml | `ci_test_standards_clang_full` | 11, libcxx; 11, libstdcxx; 14, libcxx; 14, libstdcxx; 17, libcxx; 17, libstdcxx; 20, libcxx; 20, libstdcxx; 23, libcxx; 23, libstdcxx; 26, libstdcxx |
+    | full set | ubuntu.yml | `ci_module_cpp20` | gcc:latest; silkeh/clang:latest |
+    | full set | windows.yml | `msvc_full` | Debug, Win32, latest; Debug, x64, latest; Release, Win32, default; Release, x64, latest |
+    | full set | windows.yml | `msvc-vs2026_full` | Debug, Win32, default; Debug, Win32, latest; Debug, x64, default; Release, Win32, latest; Release, x64, default; Release, x64, latest |
+    | full set | windows.yml | `msvc-arm64_full` | Release |
+    | full set | windows.yml | `clang_full` | 11.0.1; 12.0.1; 13.0.1; 14.0.6; 15.0.7; 16.0.6; 18.1.8; 19.1.7 |
+    | full set | windows.yml | `clang-cl_full` | Win32; x64 |
+    | nightly set | ubuntu.yml | `ci_infer` | - |
+    | nightly set | ubuntu.yml | `ci_static_analysis_ubuntu_nightly` | ci_test_valgrind |
+    | nightly set | ubuntu.yml | `ci_test_coverage` | - |
+    | nightly set | ubuntu.yml | `ci_cuda_example` | 11.8.0; 12.1.1; 12.6.3 |
+    | nightly set | ubuntu.yml | `ci_icpc` | - |
+    | nightly set | ubuntu.yml | `ci_icpx` | - |
+    | nightly set | ubuntu.yml | `ci_nvhpc` | - |
+    | nightly set | ubuntu.yml | `ci_test_arm64` | - |
+    | nightly set | windows.yml | `mingw_nightly` | x64 |
+    <!-- ci_jobs: end -->
+
 ## C++ language compliance and compiler compatibility
 
 !!! success "Requirement: Compiler support"

docs/mkdocs/docs/images/qa_pipeline.svg

@@ -1,26 +1,31 @@
-<svg class="nj-fig nj-exceptions-qa nj-exceptions-qa--wide" viewBox="0 0 760 808" role="img" aria-labelledby="nj-qa-title-w nj-qa-desc-w" xmlns="http://www.w3.org/2000/svg">
+<svg class="nj-fig nj-exceptions-qa nj-exceptions-qa--wide" viewBox="0 0 760 862" role="img" aria-labelledby="nj-qa-title-w nj-qa-desc-w" xmlns="http://www.w3.org/2000/svg">
 <title id="nj-qa-title-w">Quality assurance pipeline</title>
-<desc id="nj-qa-desc-w">Every push or pull request starts these checks in parallel: Build matrix (every push / PR): 50+ compilers: G&#8203;CC, Clang, M&#8203;SVC, AppleClang, Intel, NVIDIA, ... C++11, 14, 17, 20, 23, and 26 libc++ and libstdc++ warnings: Clang -Weverything, G&#8203;CC 300+ warnings; Unit tests (doctest) (every push / PR): every public A&#8203;PI function every exception id and message all Unicode code points single header and split headers custom number, string, array, and object types; Coverage (every push / PR): unit tests cover all lines of the code base; Static analysis (every push / PR, scheduled): Clang-Tidy, Cppcheck, Infer Clang Static Analyzer (52 checkers), I&#8203;WYU, Codacy CodeQL, Semgrep, Flawfinder (also scheduled); Dynamic analysis (every push / PR): runtime assertions Valgrind (Memcheck) address and undefined behavior sanitizers, integer overflow, nullability violations; Fuzzing (every PR, continuous): CIFuzz on every pull request OSS-Fuzz: billions of inputs every crash fixed with a reproducing unit test; Style (every push / PR): Artistic Style (astyle), enforced in the C&#8203;I cpplint with 61 rules; Docs and examples (every push / PR, scheduled): every documentation example is tested; changed output fails site built with warnings as errors; links checked regularly (scheduled); Integration, supply chain (every push / PR, scheduled): CMake 3.5, 3.31.6, and 4.0.0 Meson, Swift Package Manager dependency review on every PR Dependabot daily, OpenSSF Scorecard, R&#8203;EUSE. When they pass, the change is merged into develop; a release is made only when no vulnerability alert is open.</desc>
+<desc id="nj-qa-desc-w">A push or pull request starts these checks; the badges say when each runs: Build matrix (every push / PR, before merge): 50+ compilers: G&#8203;CC, Clang, M&#8203;SVC, AppleClang, Intel, NVIDIA, ... C++11, 14, 17, 20, 23, and 26 libc++ and libstdc++ warnings: Clang -Weverything, G&#8203;CC 300+ warnings a subset on every push and PR, all before merge; Intel, NVIDIA, C&#8203;UDA, and ARM64 nightly; Unit tests (doctest) (every push / PR): every public A&#8203;PI function every exception id and message all Unicode code points single header and split headers custom number, string, array, and object types; Coverage (nightly): unit tests cover all lines of the code base; Static analysis (every push / PR, scheduled): Clang-Tidy, Cppcheck, Infer Clang Static Analyzer (52 checkers), I&#8203;WYU, Codacy CodeQL, Semgrep, Flawfinder (also scheduled); Infer nightly; Dynamic analysis (every push / PR, nightly): runtime assertions Valgrind (Memcheck), nightly address and undefined behavior sanitizers, integer overflow, nullability violations; Fuzzing (every PR, continuous): CIFuzz on every pull request OSS-Fuzz: billions of inputs every crash fixed with a reproducing unit test; Style (every push / PR): Artistic Style (astyle), enforced in the C&#8203;I cpplint with 61 rules; Docs and examples (every push / PR, scheduled): every documentation example is tested; changed output fails site built with warnings as errors; links checked regularly (scheduled); Integration, supply chain (every push / PR, scheduled): CMake 3.5, 3.31.6, and 4.0.0 Meson, Swift Package Manager dependency review on every PR Dependabot daily, OpenSSF Scorecard, R&#8203;EUSE. When they pass, the change is merged into develop; a release is made only when no vulnerability alert is open.</desc>
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-<rect class="nj-exceptions-groupbox" x="12" y="70" width="736" height="594" rx="12"/>
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 <text class="nj-exceptions-line" x="40" y="206">AppleClang, Intel, NVIDIA, ...</text>
 <text class="nj-exceptions-line" x="40" y="224">C++11, 14, 17, 20, 23, and 26</text>
 <text class="nj-exceptions-line" x="40" y="242">libc++ and libstdc++</text>
 <text class="nj-exceptions-line" x="40" y="260">warnings: Clang -Weverything,</text>
 <text class="nj-exceptions-line" x="40" y="278">G&#8203;CC 300+ warnings</text>
+<text class="nj-exceptions-line" x="40" y="296">a subset on every push and PR,</text>
+<text class="nj-exceptions-line" x="40" y="314">all before merge; Intel, NVIDIA,</text>
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-<text class="nj-exceptions-ctitle" x="40" y="331">Unit tests (doctest)</text>
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-<text class="nj-exceptions-line" x="40" y="384">every public A&#8203;PI function</text>
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+<text class="nj-exceptions-line" x="40" y="456">every exception id and message</text>
-<text class="nj-exceptions-line" x="40" y="420">all Unicode code points</text>
+<text class="nj-exceptions-line" x="40" y="474">all Unicode code points</text>
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+<text class="nj-exceptions-line" x="40" y="510">custom number, string, array,</text>
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-<text class="nj-exceptions-ctitle" x="40" y="527">Coverage</text>
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-<rect class="nj-exceptions-badge nj-exceptions-badge--push" x="40" y="538" width="110.5" height="20" rx="10"/>
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-<text class="nj-exceptions-line" x="40" y="722">Clang Static Analyzer (52</text>
+<text class="nj-exceptions-line" x="40" y="776">Clang Static Analyzer (52</text>
-<text class="nj-exceptions-line" x="40" y="740">checkers), I&#8203;WYU, Codacy</text>
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-<text class="nj-exceptions-line" x="40" y="758">CodeQL, Semgrep, Flawfinder</text>
+<text class="nj-exceptions-line" x="40" y="812">CodeQL, Semgrep, Flawfinder</text>
-<text class="nj-exceptions-line" x="40" y="776">(also scheduled)</text>
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-<text class="nj-exceptions-line" x="40" y="918">address and undefined behavior</text>
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-<text class="nj-exceptions-badgetext nj-exceptions-badgetext--cont" x="151.9" y="1032">continuous</text>
+<text class="nj-exceptions-badgetext nj-exceptions-badgetext--cont" x="151.9" y="1086">continuous</text>
-<text class="nj-exceptions-line" x="40" y="1060">CIFuzz on every pull request</text>
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-<text class="nj-exceptions-line" x="40" y="1078">OSS-Fuzz: billions of inputs</text>
+<text class="nj-exceptions-line" x="40" y="1132">OSS-Fuzz: billions of inputs</text>
-<text class="nj-exceptions-line" x="40" y="1096">every crash fixed with a</text>
+<text class="nj-exceptions-line" x="40" y="1150">every crash fixed with a</text>
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-<text class="nj-exceptions-ctitle" x="40" y="1167">Style</text>
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-<text class="nj-exceptions-line" x="40" y="1220">Artistic Style (astyle),</text>
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-<text class="nj-exceptions-line" x="40" y="1238">enforced in the C&#8203;I</text>
+<text class="nj-exceptions-line" x="40" y="1292">enforced in the C&#8203;I</text>
-<text class="nj-exceptions-line" x="40" y="1256">cpplint with 61 rules</text>
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-<text class="nj-exceptions-line" x="40" y="1362">every documentation example is</text>
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+<text class="nj-exceptions-line" x="40" y="1434">tested; changed output fails</text>
-<text class="nj-exceptions-line" x="40" y="1398">site built with warnings</text>
+<text class="nj-exceptions-line" x="40" y="1452">site built with warnings</text>
-<text class="nj-exceptions-line" x="40" y="1416">as errors; links checked</text>
+<text class="nj-exceptions-line" x="40" y="1470">as errors; links checked</text>
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-<text class="nj-exceptions-ctitle" x="40" y="1487">Integration, supply chain</text>
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+<text class="nj-exceptions-line" x="40" y="1612">Meson, Swift Package Manager</text>
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+<rect class="nj-exceptions-stage nj-exceptions-stage--merge" x="65" y="1724" width="230" height="34" rx="17"/>
-<text class="nj-exceptions-stagetext" x="180" y="1692">merge into develop</text>
+<text class="nj-exceptions-stagetext" x="180" y="1746">merge into develop</text>
-<line class="nj-exceptions-edge" x1="180" y1="1704" x2="180" y2="1730" marker-end="url(#nj-qa-arrow-n)"/>
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+<rect class="nj-exceptions-stage nj-exceptions-stage--merge" x="30" y="1786" width="300" height="46" rx="23"/>
-<text class="nj-exceptions-stagetext" x="180" y="1754">release</text>
+<text class="nj-exceptions-stagetext" x="180" y="1808">release</text>
-<text class="nj-exceptions-stagesub" x="180" y="1770">no open vulnerability alert</text>
+<text class="nj-exceptions-stagesub" x="180" y="1824">no open vulnerability alert</text>
 </svg>

docs/mkdocs/scripts/figures/qa_pipeline.py

@@ -22,19 +22,24 @@ P = "nj-exceptions-"
 TRIGGERS = {
     "push": ("every push / PR", "push"),
     "pr": ("every PR", "push"),
+    "merge": ("before merge", "push"),
+    "nightly": ("nightly", "sched"),
     "sched": ("scheduled", "sched"),
     "cont": ("continuous", "cont"),
 }
 
 # title, triggers, lines (at most 31 characters, so they fit a card of the three-column drawing)
 LANES = [
-    ("Build matrix", ["push"], [
+    ("Build matrix", ["push", "merge"], [
         "50+ compilers: GCC, Clang, MSVC,",
         "AppleClang, Intel, NVIDIA, ...",
         "C++11, 14, 17, 20, 23, and 26",
         "libc++ and libstdc++",
         "warnings: Clang -Weverything,",
         "GCC 300+ warnings",
+        "a subset on every push and PR,",
+        "all before merge; Intel, NVIDIA,",
+        "CUDA, and ARM64 nightly",
     ]),
     ("Unit tests (doctest)", ["push"], [
         "every public API function",
@@ -44,7 +49,7 @@ LANES = [
         "custom number, string, array,",
         "and object types",
     ]),
-    ("Coverage", ["push"], [
+    ("Coverage", ["nightly"], [
         "unit tests cover all lines",
         "of the code base",
     ]),
@@ -53,11 +58,11 @@ LANES = [
         "Clang Static Analyzer (52",
         "checkers), IWYU, Codacy",
         "CodeQL, Semgrep, Flawfinder",
-        "(also scheduled)",
+        "(also scheduled); Infer nightly",
     ]),
-    ("Dynamic analysis", ["push"], [
+    ("Dynamic analysis", ["push", "nightly"], [
         "runtime assertions",
-        "Valgrind (Memcheck)",
+        "Valgrind (Memcheck), nightly",
         "address and undefined behavior",
         "sanitizers, integer overflow,",
         "nullability violations",
@@ -178,7 +183,7 @@ def drawing(W, cols, suffix):
     defs = ('<defs><marker id="%s" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto">'
             '<path class="fg-head" d="M0 1 L10 5 L0 9 z"/></marker></defs>' % mid)
     tid, did = "nj-qa-title-" + suffix, "nj-qa-desc-" + suffix
-    desc = ("Every push or pull request starts these checks in parallel: " +
+    desc = ("A push or pull request starts these checks; the badges say when each runs: " +
             "; ".join("%s (%s): %s" % (t, ", ".join(TRIGGERS[k][0] for k in trig), " ".join(lines)) for t, trig, lines in LANES) +
             ". When they pass, the change is merged into develop; a release is made only when no vulnerability alert is open.")
     out = ['<svg class="nj-fig %sqa %sqa--%s" viewBox="0 0 %d %d" role="img" aria-labelledby="%s %s" xmlns="http://www.w3.org/2000/svg">'

tools/check_path_filters/README.md

@@ -0,0 +1,34 @@
+# check_path_filters
+
+The compiler workflows [`ubuntu.yml`](../../.github/workflows/ubuntu.yml),
+[`macos.yml`](../../.github/workflows/macos.yml), and [`windows.yml`](../../.github/workflows/windows.yml) skip pull
+requests that change only files no compiler job reads: the documentation, Markdown files, GitHub metadata, other
+workflows, and the license files. Pushes to `develop`, `master`, and `release/*` always run them. The documentation,
+license, and path-filter checks run in [`repository_checks.yml`](../../.github/workflows/repository_checks.yml), which
+has no path filter.
+
+The filter starts with `'**'` and excludes these files explicitly, so a new file runs the compiler workflows unless it
+is excluded on purpose. [`check_path_filters.py`](check_path_filters.py) holds the filter (`PATHS`) and checks that
+
+- each of the three workflows has exactly this filter, with its own workflow file included,
+- the CI targets that read excluded files (`UNFILTERED_TARGETS`) do not run in these workflows, and
+- no file the filter keeps (sources, tests, build files, tools, workflows) mentions an excluded file or directory
+  outside a comment line, unless the mention is listed in `KNOWN_REFERENCES` with a reason.
+
+When the check reports a mention, decide whether a compiler job reads that file:
+
+- If it does, include the file in `PATHS` after the exclusions (as `package_managers.md` and the Swift example are) and
+  copy the new filter into the three workflows.
+- If it does not, add the mention to `KNOWN_REFERENCES` with the reason.
+
+Run the check with
+
+```shell
+python3 tools/check_path_filters/check_path_filters.py
+```
+
+To see which workflows a pull request would run, pass the changed files:
+
+```shell
+python3 tools/check_path_filters/check_path_filters.py --changed $(git diff --name-only origin/develop)
+```

tools/check_path_filters/check_path_filters.py

@@ -0,0 +1,273 @@
+#!/usr/bin/env python3
+"""Check the path filters of the compiler workflows.
+
+ubuntu.yml, macos.yml and windows.yml skip pull requests that change only files
+no compiler job reads (documentation, Markdown files, GitHub metadata, license
+files). The filter starts with '**' and excludes these files explicitly, so a
+new file runs the workflows unless it is excluded on purpose.
+
+The script checks that
+
+- each of the three workflows has exactly the filter defined in PATHS below,
+  with its own workflow file included, and
+- no tracked file that the filter keeps (sources, tests, build files, tools,
+  workflows) mentions a file the filter excludes, unless the mention is listed
+  in KNOWN_REFERENCES with the reason why it does not matter.
+
+A mention found this way must either be added to PATHS as an included path
+(the file is read by a compiler job) or to KNOWN_REFERENCES (it is not).
+
+With --changed FILE..., the script prints instead which workflows a pull
+request changing these files would run.
+"""
+
+import argparse
+import os
+import re
+import subprocess  # nosec B404
+import sys
+
+REPO_ROOT = os.path.normpath(os.path.join(sys.path[0], '..', '..'))
+SELF = 'tools/check_path_filters/check_path_filters.py'
+
+WORKFLOWS = ['.github/workflows/ubuntu.yml', '.github/workflows/macos.yml', '.github/workflows/windows.yml']
+
+# The pull_request paths filter of the workflows above; '{workflow}' is replaced
+# with the workflow's own file. GitHub applies the patterns in order: a file
+# matching a later pattern is included ('pattern') or excluded ('!pattern').
+PATHS = [
+    '**',
+    '!docs/**',
+    '!**.md',
+    '!.github/*',
+    '!.github/ISSUE_TEMPLATE/**',
+    '!.github/external_ci/**',
+    '!.github/workflows/**',
+    '!.reuse/**',
+    '!LICENSES/**',
+    '!CITATION.cff',
+    '!REUSE.toml',
+    # read by tools/check_build_options in the ci_meson_install job (ubuntu.yml)
+    'docs/mkdocs/docs/integration/package_managers.md',
+    # built by the swiftpm job (macos.yml)
+    'docs/mkdocs/docs/integration/swift/**',
+    '{workflow}',
+]
+
+# Mentions of excluded files that no job of the three workflows depends on:
+# (file that mentions it, the mention, reason)
+KNOWN_REFERENCES = [
+    ('cmake/ci.cmake', 'docs/', 'ci_test_examples; runs in repository_checks.yml, which has no path filter'),
+    ('cmake/ci.cmake', 'docs/mkdocs/', 'ci_test_build_documentation and ci_test_documentation_mermaid; they run in '
+                                       'repository_checks.yml, which has no path filter'),
+    ('cmake/ci.cmake', 'docs/mkdocs/docs/examples/', 'indentation check of ci_test_amalgamation; the same check runs in '
+                                                     'check_amalgamation.yml, which has no path filter'),
+    ('Makefile', 'docs/mkdocs/docs/examples/', 'make pretty; runs in check_amalgamation.yml, which has no path filter'),
+    ('Makefile', 'ChangeLog.md', 'make ChangeLog.md writes the file; no CI job runs it'),
+    ('Makefile', 'tests/fuzzing.md', 'help text'),
+    ('Makefile', 'tools/generate_natvis/README.md', 'help text'),
+    ('tests/src/make_test_data_available.hpp', 'README.md', 'a file of the external test data repository'),
+    ('tools/check_build_options/check_build_options.py', 'docs/', 'builds the path of package_managers.md, which '
+                                                                  'PATHS includes'),
+    ('tools/ci_jobs/ci_jobs.py', 'docs/mkdocs/docs/community/quality_assurance.md',
+     'checks the job table; runs in repository_checks.yml, which has no path filter'),
+    ('tools/ci_jobs/ci_jobs.py', '.github/workflows/repository_checks.yml', 'read by --compare, a manual check'),
+    ('tools/ci_jobs/ci_jobs.py', '.github/workflows/check_amalgamation.yml', 'read by --compare, a manual check'),
+]
+
+
+# CI targets that read excluded files; they must run in a workflow without a path filter
+UNFILTERED_TARGETS = ['ci_test_examples', 'ci_test_build_documentation', 'ci_test_documentation_mermaid',
+                      'ci_test_amalgamation', 'ci_reuse_compliance']
+
+
+def git_files(root):
+    # fixed command, no user input; includes new files not yet added, so a local run
+    # sees what CI sees after the commit
+    out = subprocess.check_output(['git', 'ls-files', '-z', '--cached', '--others', '--exclude-standard'], cwd=root)  # nosec B603, B607
+    return [f for f in out.decode('utf-8').split('\0') if f]
+
+
+def glob_to_regex(pattern):
+    """Translate a GitHub Actions path pattern to a regular expression."""
+    regex = ''
+    i = 0
+    while i < len(pattern):
+        if pattern.startswith('**', i):
+            regex += '.*'
+            i += 2
+        elif pattern[i] == '*':
+            regex += '[^/]*'
+            i += 1
+        elif pattern[i] == '?':
+            regex += '[^/]'
+            i += 1
+        else:
+            regex += re.escape(pattern[i])
+            i += 1
+    return re.compile(regex + r'\Z')
+
+
+def compile_filter(paths, workflow):
+    return [(p.startswith('!'), glob_to_regex(p.lstrip('!').replace('{workflow}', workflow))) for p in paths]
+
+
+def included(compiled, path):
+    result = False
+    for negated, regex in compiled:
+        if regex.match(path):
+            result = not negated
+    return result
+
+
+def read_filter(root, workflow):
+    """Return the pull_request paths list of a workflow file."""
+    with open(os.path.join(root, workflow), encoding='utf-8') as f:
+        lines = f.read().splitlines()
+    paths = None
+    in_pull_request = False
+    for line in lines:
+        if re.match(r'^  pull_request:', line):
+            in_pull_request = True
+            continue
+        if in_pull_request:
+            if re.match(r'^  \S', line) or re.match(r'^\S', line):
+                break
+            if re.match(r'^    paths:\s*$', line):
+                paths = []
+                continue
+            m = re.match(r"^      - '(.*)'\s*(#.*)?$", line)
+            if paths is not None and m:
+                paths.append(m.group(1))
+            elif paths is not None and line.strip() and not line.strip().startswith('#'):
+                break
+    return paths
+
+
+TOKEN = re.compile(r'(["\'/]?)([\w.-]+(?:/[\w.-]+)*)')
+
+
+COMMENT_LINE = re.compile(r'^[ \t]*(//|#|/?\*|--).*$', re.MULTILINE)
+
+
+class Mentions:
+    """Finds the words and paths in a text that name an excluded file or directory."""
+
+    def __init__(self, files, excluded, is_excluded):
+        self.files = set(files)
+        self.excluded = excluded
+        self.dirs = {'/'.join(f.split('/')[:n]) for f in files for n in range(1, f.count('/') + 1)}
+        # an excluded directory: a new file in it would be excluded
+        self.excluded_dirs = {d for d in self.dirs if is_excluded(d + '/new_file')}
+        # base names that only excluded files have, e.g. 'ChangeLog.md' but not 'CMakeLists.txt'
+        self.names = {os.path.basename(f) for f in excluded} - {os.path.basename(f) for f in files if f not in excluded}
+
+    def find(self, text):
+        """Yield (offset, mention) for every word or path in text that names an excluded file or directory."""
+        for m in TOKEN.finditer(text):
+            parts = m.group(2).rstrip('/').split('/')
+            # a single word names a directory only in a path context, e.g. 'docs' in os.path.join('docs', ...)
+            path_context = len(parts) > 1 or m.group(1)
+            for i in range(len(parts)):
+                path = '/'.join(parts[i:])
+                if path in self.files:
+                    if path in self.excluded:
+                        yield m.start(2), path
+                    break
+                if path in self.dirs and path_context:
+                    if path in self.excluded_dirs:
+                        yield m.start(2), path + '/'
+                    break
+            else:
+                if parts[-1] in self.names and '.' in parts[-1]:
+                    yield m.start(2), parts[-1]
+
+
+def known(path, mention):
+    return any(path == file and mention == known_mention for file, known_mention, _ in KNOWN_REFERENCES)
+
+
+def check_workflows(root):
+    """Return the errors in the filters of the workflows and in the targets they run."""
+    errors = []
+    for workflow in WORKFLOWS:
+        expected = [p.replace('{workflow}', workflow) for p in PATHS]
+        actual = read_filter(root, workflow)
+        if actual != expected:
+            errors.append('{}: the pull_request paths filter differs from tools/check_path_filters/check_path_filters.py\n'
+                          '  expected: {}\n  actual:   {}'.format(workflow, expected, actual))
+        with open(os.path.join(root, workflow), encoding='utf-8') as f:
+            text = f.read()
+        errors += ['{}: runs {}, which reads excluded files; run it in repository_checks.yml'.format(workflow, target)
+                   for target in UNFILTERED_TARGETS if re.search(r'\b' + target + r'\b', text)]
+    return errors
+
+
+def scanned_text(root, path):
+    """Return the text of a kept file without comment lines and without the filter itself, or None to skip it."""
+    # third-party code and Markdown files read nothing; this script lists the excluded files
+    if path.startswith('tests/thirdparty/') or path.endswith('.md') or path == SELF:
+        return None
+    try:
+        with open(os.path.join(root, path), encoding='utf-8') as f:
+            # a mention in a comment line reads nothing; keep the line numbers
+            text = COMMENT_LINE.sub('', f.read())
+    except (UnicodeDecodeError, OSError):
+        return None
+    if path in WORKFLOWS:
+        # the filter itself lists the excluded files
+        for p in PATHS:
+            text = text.replace("      - '{}'".format(p.replace('{workflow}', path)), '')
+    return text
+
+
+def check_mentions(root, files, excluded, finder):
+    """Return an error for every mention of an excluded file in a kept file that KNOWN_REFERENCES does not list."""
+    errors = []
+    for path in sorted(set(files) - excluded):
+        text = scanned_text(root, path)
+        reported = set()
+        for offset, mention in finder.find(text or ''):
+            if mention not in reported and not known(path, mention):
+                reported.add(mention)
+                line = text.count('\n', 0, offset) + 1
+                errors.append('{}:{}: mentions excluded {}; include it in PATHS if a compiler job reads it, '
+                              'or add it to KNOWN_REFERENCES'.format(path, line, mention))
+    return errors
+
+
+def check(root):
+    files = git_files(root)
+    union = [compile_filter(PATHS, w) for w in WORKFLOWS]
+
+    def is_excluded(path):
+        return not any(included(c, path) for c in union)
+
+    excluded = {f for f in files if is_excluded(f)}
+    errors = check_workflows(root) + check_mentions(root, files, excluded, Mentions(files, excluded, is_excluded))
+    for e in errors:
+        print(e)
+    if not errors:
+        print('path filters OK: {} of {} tracked files skip the compiler workflows'.format(len(excluded), len(files)))
+    return 1 if errors else 0
+
+
+def explain(changed):
+    for workflow in WORKFLOWS:
+        compiled = compile_filter(PATHS, workflow)
+        hits = [f for f in changed if included(compiled, f)]
+        print('{}: {}'.format(workflow, 'runs ({})'.format(', '.join(hits[:3]) + (' ...' if len(hits) > 3 else ''))
+                                       if hits else 'skipped'))
+    return 0
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__.splitlines()[0])
+    parser.add_argument('--root', default=REPO_ROOT, help='repository root')
+    parser.add_argument('--changed', nargs='+', metavar='FILE', help='show which workflows these changed files run')
+    args = parser.parse_args()
+    return explain(args.changed) if args.changed else check(args.root)
+
+
+if __name__ == '__main__':
+    sys.exit(main())

tools/ci_jobs/README.md

@@ -0,0 +1,30 @@
+# ci_jobs
+
+The jobs of the compiler workflows [`ubuntu.yml`](../../.github/workflows/ubuntu.yml),
+[`macos.yml`](../../.github/workflows/macos.yml), and [`windows.yml`](../../.github/workflows/windows.yml) are split into
+three sets, chosen by each job's
+`if:` condition (see [How CI runs](https://json.nlohmann.me/community/quality_assurance/#how-ci-runs)):
+
+- **PR set**: every push to a pull request, and every push to `develop`, `master`, and `release/*`;
+- **full set**: after the PR set passed, on pull requests with the label "🚀 ready to merge" and on every push;
+- **nightly set**: every night on `develop`, on every push to `master` and `release/*`, and when started by hand.
+
+A matrix whose entries belong to different sets is split into one job per set: the full-set job gets the suffix
+`_full`, the nightly-set job `_nightly`, and both share their steps with the PR-set job through YAML anchors.
+
+[`ci_jobs.py`](ci_jobs.py) checks that
+
+- every job has the `if:` condition of exactly one set (the conditions are in `SETS`),
+- every full-set job waits for (`needs:`) exactly the PR set of its workflow, and `nightly_report` for exactly the
+  nightly set, and
+- the job table in [`quality_assurance.md`](../../docs/mkdocs/docs/community/quality_assurance.md) is up to date.
+
+```shell
+python3 -m venv venv && venv/bin/pip install -r tools/ci_jobs/requirements.txt
+venv/bin/python tools/ci_jobs/ci_jobs.py                       # check
+venv/bin/python tools/ci_jobs/ci_jobs.py --markdown            # print the job table for the documentation
+venv/bin/python tools/ci_jobs/ci_jobs.py --compare origin/develop  # list configurations added or removed since develop
+```
+
+Use `--compare` when changing the workflows: a configuration that disappears fails it, so no compiler, version, or
+standard is dropped by accident when jobs are split, merged, or moved between sets.

tools/ci_jobs/ci_jobs.py

@@ -0,0 +1,231 @@
+#!/usr/bin/env python3
+"""List and check the jobs of the compiler workflows and the set each job belongs to.
+
+The jobs of the compiler workflows belong to one of three sets, chosen by the
+job's `if:` condition:
+
+- PR set: every pull request push and every push,
+- full set: after the PR set passed, on pushes and on pull requests with the
+  "🚀 ready to merge" label,
+- nightly set: nightly on develop, on pushes to master and release/*, and when
+  started by hand.
+
+The script checks that every job belongs to exactly one set, that the full set
+of a workflow waits for its whole PR set, that the nightly report waits for the
+whole nightly set, and that the job table in
+docs/mkdocs/docs/community/quality_assurance.md is up to date.
+
+  --markdown       print the job table for the documentation
+  --compare REF    list the configurations (job and matrix values) added or
+                   removed since the git revision REF; fails if one was removed
+"""
+
+import argparse
+import collections
+import itertools
+import os
+import re
+import subprocess  # nosec B404
+import sys
+
+import yaml
+
+REPO_ROOT = os.path.normpath(os.path.join(sys.path[0], '..', '..'))
+DOCS = 'docs/mkdocs/docs/community/quality_assurance.md'
+BEGIN, END = '<!-- ci_jobs: begin -->', '<!-- ci_jobs: end -->'
+
+WORKFLOWS = ['.github/workflows/ubuntu.yml', '.github/workflows/macos.yml', '.github/workflows/windows.yml']
+TIERED = WORKFLOWS
+# --compare also counts the jobs of these workflows, so a job moved between workflows is not a removed one
+COMPARED = WORKFLOWS + ['.github/workflows/repository_checks.yml', '.github/workflows/check_amalgamation.yml']
+
+LABEL = '🚀 ready to merge'
+SETS = collections.OrderedDict([
+    ('PR set', "${{ github.event_name != 'schedule' && (github.event.action != 'labeled' || "
+               "github.event.label.name == '" + LABEL + "') }}"),
+    ('full set', "${{ github.event_name == 'push' || github.event_name == 'workflow_dispatch' || "
+                 "contains(github.event.pull_request.labels.*.name, '" + LABEL + "') }}"),
+    ('nightly set', "${{ github.event_name == 'schedule' || github.event_name == 'workflow_dispatch' || "
+                    "(github.event_name == 'push' && github.ref != 'refs/heads/develop') }}"),
+])
+UNTIERED = 'every push and PR'
+REPORT_JOB = 'nightly_report'
+
+# a job split by set keeps its name and gets one of these suffixes
+SUFFIXES = {'full set': '_full', 'nightly set': '_nightly'}
+
+
+def read(root, path, ref=None):
+    if ref is None:
+        with open(os.path.join(root, path), encoding='utf-8') as f:
+            return f.read()
+    # fixed command; ref is a git revision given on the command line
+    return subprocess.check_output(['git', 'show', '{}:{}'.format(ref, path)], cwd=root,  # nosec B603, B607
+                                   stderr=subprocess.DEVNULL).decode('utf-8')
+
+
+def add_include(combos, keys, inc):
+    """Apply one include entry: extend the matching configurations, or add it as a new one."""
+    matching = [c for c in combos if all(c[k] == v for k, v in inc.items() if k in keys)]
+    for c in matching:
+        c.update({k: v for k, v in inc.items() if k not in keys})
+    if not matching:
+        combos.append(dict(inc))
+
+
+def expand(matrix):
+    """Return the configurations of a job's strategy.matrix like GitHub Actions does."""
+    if not matrix:
+        return [{}]
+    keys = [k for k in matrix if k not in ('include', 'exclude')]
+    if not keys:
+        # a matrix of only include entries runs each entry
+        return [dict(inc) for inc in matrix.get('include') or []]
+    combos = [dict(zip(keys, values)) for values in itertools.product(*(matrix[k] for k in keys))]
+    for ex in matrix.get('exclude') or []:
+        combos = [c for c in combos if any(c.get(k) != v for k, v in ex.items())]
+    for inc in matrix.get('include') or []:
+        add_include(combos, keys, inc)
+    return combos
+
+
+def jobs_of(root, workflow, ref=None):
+    """Yield (job id, set, list of configurations) for every job of a workflow."""
+    data = yaml.safe_load(read(root, workflow, ref))
+    for job_id, job in data['jobs'].items():
+        condition = job.get('if')
+        job_set = UNTIERED if condition is None else next((s for s, c in SETS.items() if c == condition), None)
+        matrix = (job.get('strategy') or {}).get('matrix')
+        yield job_id, job_set, job, expand(matrix)
+
+
+def base_id(job_id, job_set):
+    suffix = SUFFIXES.get(job_set)
+    return job_id[:-len(suffix)] if suffix and job_id.endswith(suffix) else job_id
+
+
+def label(config):
+    return ', '.join(str(v) for k, v in config.items() if k != 'os' or len(config) == 1)
+
+
+def configurations(root, ref=None):
+    """Return a Counter of (job name without set suffix, configuration) over the compared workflows."""
+    result = collections.Counter()
+    for workflow in COMPARED:
+        try:
+            jobs = list(jobs_of(root, workflow, ref))
+        except (OSError, subprocess.CalledProcessError):
+            continue  # the workflow does not exist in this revision
+        for job_id, job_set, _, configs in jobs:
+            if job_id == REPORT_JOB:
+                continue
+            for c in configs:
+                result[(base_id(job_id, job_set), tuple(sorted((k, str(v)) for k, v in c.items())))] += 1
+    return result
+
+
+def markdown(root):
+    rows = []
+    order = list(SETS) + [UNTIERED]
+    for workflow in WORKFLOWS:
+        for job_id, job_set, _, configs in jobs_of(root, workflow):
+            if job_id == REPORT_JOB:
+                continue
+            labels = [label(c) for c in configs if c]
+            rows.append((order.index(job_set) if job_set in order else len(order), os.path.basename(workflow), job_id,
+                         job_set or 'no set', '; '.join(labels) or '-'))
+    rows.sort(key=lambda r: (r[0], r[1]))
+    lines = ['| Set | Workflow | Job | Configurations |', '|-----|----------|-----|----------------|']
+    lines += ['| {} | {} | `{}` | {} |'.format(s, w, j, c) for _, w, j, s, c in rows]
+    return lines
+
+
+def check_sets(workflow, jobs):
+    """Return the errors in the sets of a tiered workflow's jobs and the jobs of each set."""
+    errors = []
+    by_set = collections.defaultdict(set)
+    for job_id, job_set, _, _ in jobs:
+        if job_id == REPORT_JOB:
+            continue
+        if job_set in SETS:
+            by_set[job_set].add(job_id)
+        else:
+            errors.append('{}: job {} has an if: condition of no set; use one of the conditions in '
+                          'tools/ci_jobs/ci_jobs.py'.format(workflow, job_id))
+    return errors, by_set
+
+
+def check_needs(workflow, jobs, by_set):
+    """Return the errors in the needs: of a tiered workflow's jobs."""
+    required = {'full set': by_set['PR set'], 'PR set': set(), 'nightly set': set()}
+    errors = []
+    for job_id, job_set, job, _ in jobs:
+        needs = job.get('needs') or []
+        needs = {needs} if isinstance(needs, str) else set(needs)
+        expected = by_set['nightly set'] if job_id == REPORT_JOB else required.get(job_set, needs)
+        if needs != expected:
+            errors.append('{}: job {} must need exactly: {}'.format(workflow, job_id, ', '.join(sorted(expected)) or 'no job'))
+    return errors
+
+
+def check_docs(root):
+    """Return an error if the job table in the documentation is not up to date."""
+    text = read(root, DOCS)
+    block = re.search(re.escape(BEGIN) + r'\n(.*?)\n[ \t]*' + re.escape(END), text, re.S)
+    if not block:
+        return ['{}: markers {} and {} not found'.format(DOCS, BEGIN, END)]
+    indent = re.match(r'[ \t]*', block.group(1)).group(0)
+    if block.group(1) != '\n'.join(indent + line for line in markdown(root)):
+        return ['{}: the job table is out of date; replace it with the output of '
+                'python3 tools/ci_jobs/ci_jobs.py --markdown'.format(DOCS)]
+    return []
+
+
+def check(root):
+    errors = []
+    for workflow in TIERED:
+        jobs = list(jobs_of(root, workflow))
+        set_errors, by_set = check_sets(workflow, jobs)
+        errors += set_errors + check_needs(workflow, jobs, by_set)
+    errors += check_docs(root)
+
+    for e in errors:
+        print(e)
+    if not errors:
+        counts = collections.Counter()
+        for workflow in WORKFLOWS:
+            for job_id, job_set, _, configs in jobs_of(root, workflow):
+                if job_id != REPORT_JOB:
+                    counts[job_set] += len(configs)
+        print('CI jobs OK: ' + ', '.join('{} {}'.format(n, s) for s, n in counts.items()))
+    return 1 if errors else 0
+
+
+def compare(root, ref):
+    before, after = configurations(root, ref), configurations(root)
+    removed, added = before - after, after - before
+    for title, diff in (('removed', removed), ('added', added)):
+        for job, config in sorted(diff.elements()):
+            print('{}: {} ({})'.format(title, job, ', '.join('{}={}'.format(k, v) for k, v in config)))
+    print('{} configurations before, {} after; {} removed, {} added'.format(
+        sum(before.values()), sum(after.values()), sum(removed.values()), sum(added.values())))
+    return 1 if removed else 0
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__.splitlines()[0])
+    parser.add_argument('--root', default=REPO_ROOT, help='repository root')
+    group = parser.add_mutually_exclusive_group()
+    group.add_argument('--markdown', action='store_true', help='print the job table for the documentation')
+    group.add_argument('--compare', metavar='REF', help='list the configurations added or removed since REF')
+    args = parser.parse_args()
+    if args.markdown:
+        print('\n'.join(markdown(args.root)))
+        return 0
+    if args.compare:
+        return compare(args.root, args.compare)
+    return check(args.root)
+
+
+if __name__ == '__main__':
+    sys.exit(main())

tools/ci_jobs/requirements.txt

@@ -0,0 +1 @@
+PyYAML==6.0.3