Speed up C++ CI and cover GCC 8–11 compatibility

.github/workflows/cmake-multi-platform.yml

@@ -11,7 +11,14 @@ on:
 permissions:
   contents: read
 
+# New PR commits supersede older checks; keep every non-PR run independent.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && format('pr-{0}', github.event.pull_request.number) || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 env:
+  # Bound compiler memory use while taking advantage of multiple runner cores.
+  CMAKE_BUILD_PARALLEL_LEVEL: "2"
   CSV_FETCHCONTENT_BASE_DIR: ${{ github.workspace }}/.cache/fetchcontent
 
 jobs:

.github/workflows/codeql.yml

@@ -8,6 +8,15 @@ on:
   schedule:
     - cron: '0 2 * * 0'  # Weekly on Sunday at 2 AM UTC
 
+# New PR commits supersede older checks; keep every non-PR run independent.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && format('pr-{0}', github.event.pull_request.number) || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+env:
+  # Bound compiler memory use while taking advantage of multiple runner cores.
+  CMAKE_BUILD_PARALLEL_LEVEL: "2"
+
 jobs:
   analyze:
     name: CodeQL C++
@@ -31,15 +40,10 @@ jobs:
     - name: Initialize CodeQL
       uses: github/codeql-action/init@v3
       with:
-        language: ${{ matrix.language }}
+        languages: ${{ matrix.language }}
         queries: security-and-quality
         config-file: ./.github/codeql/codeql-config.yml
-
-    - name: Install dependencies
-      run: |
-        sudo apt-get update
-        sudo apt-get install -y build-essential cmake
-
+
     - name: Configure CMake
       run: |
         mkdir -p build

.github/workflows/compat-edge-cases.yml

@@ -3,7 +3,14 @@ name: Compatibility Edge Cases
 permissions:
   contents: read
 
+# New PR commits supersede older checks; keep every non-PR run independent.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && format('pr-{0}', github.event.pull_request.number) || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 env:
+  # Bound compiler memory use while taking advantage of multiple runner cores.
+  CMAKE_BUILD_PARALLEL_LEVEL: "2"
   CSV_FETCHCONTENT_BASE_DIR: ${{ github.workspace }}/.cache/fetchcontent
 
 on:
@@ -29,10 +36,8 @@ jobs:
     runs-on: windows-latest
 
     steps:
-    - name: Checkout repository and submodules
+    - name: Checkout repository
       uses: actions/checkout@v5
-      with:
-        submodules: recursive
 
     - name: Set up MSVC developer command prompt
       uses: ilammy/msvc-dev-cmd@v1
@@ -43,18 +48,13 @@ jobs:
       with:
         run: "false"
 
-    - name: Cache CMake FetchContent dependencies
-      uses: actions/cache@v5
-      with:
-        path: ${{ env.CSV_FETCHCONTENT_BASE_DIR }}
-        key: fetchcontent-${{ runner.os }}-msvc-no-zc-${{ hashFiles('CMakeLists.txt', 'tests/CMakeLists.txt') }}
-
     - name: Configure CMake (for single-header generation)
       run: >
         cmake -S ${{ github.workspace }}
         -B ${{ github.workspace }}/build/no-zc-cplusplus
         -DCSV_CXX_STANDARD=20
         -DCSV_BUILD_PROGRAMS=OFF
+        -DCSV_BUILD_TESTS=OFF
         -DBUILD_PYTHON=OFF
         -DCSV_SINGLE_HEADER_EXECUTABLE="${{ steps.single-header.outputs.executable }}"
 

.github/workflows/coverage.yml

@@ -10,7 +10,14 @@ permissions:
   contents: read
   pull-requests: write
 
+# New PR commits supersede older checks; keep every non-PR run independent.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && format('pr-{0}', github.event.pull_request.number) || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 env:
+  # Bound compiler memory use while taking advantage of multiple runner cores.
+  CMAKE_BUILD_PARALLEL_LEVEL: "2"
   CSV_FETCHCONTENT_BASE_DIR: ${{ github.workspace }}/.cache/fetchcontent
 
 jobs:

.github/workflows/gcc-compatibility.yml

@@ -0,0 +1,104 @@
+name: Older GCC compatibility
+
+on:
+  push:
+    branches: [master]
+    paths:
+      - "include/**"
+      - "CMakeLists.txt"
+      - "cmake/**"
+      - "single_header.json"
+      - "tests/compatibility/gcc/**"
+      - ".github/workflows/gcc-compatibility.yml"
+  pull_request:
+    branches: [master]
+    paths:
+      - "include/**"
+      - "CMakeLists.txt"
+      - "cmake/**"
+      - "single_header.json"
+      - "tests/compatibility/gcc/**"
+      - ".github/workflows/gcc-compatibility.yml"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && format('pr-{0}', github.event.pull_request.number) || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+jobs:
+  gcc:
+    name: GCC ${{ matrix.version }} / C++17
+    runs-on: ubuntu-24.04
+    timeout-minutes: 15
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - version: "8.5.0"
+            image: gcc:8.5.0
+          - version: "9.5.0"
+            image: gcc:9.5.0-bullseye
+          - version: "10.5.0"
+            image: gcc:10.5.0-bullseye
+          # The first GCC 11 release covers the floating charconv boundary.
+          - version: "11.1.0"
+            image: gcc:11.1.0-bullseye
+    env:
+      GCC_IMAGE: ${{ matrix.image }}
+      GCC_VERSION: ${{ matrix.version }}
+    steps:
+      # Keep JavaScript actions on the host; old images may lack Node's glibc.
+      - uses: actions/checkout@v5
+
+      - name: Install single_header
+        id: single-header
+        uses: vincentlaucsb/single_header@0.1.0
+        with:
+          run: "false"
+
+      - name: Generate canonical single header
+        run: |
+          cmake -S . -B build/gcc-header -DCSV_CXX_STANDARD=17 \
+            -DCSV_BUILD_TESTS=OFF -DCSV_BUILD_PROGRAMS=OFF \
+            -DCSV_SINGLE_HEADER_EXECUTABLE="${{ steps.single-header.outputs.executable }}"
+          cmake --build build/gcc-header --target generate_single_header
+
+      - name: Prepare portable CMake and compiler
+        id: toolchain
+        run: |
+          mkdir -p "$RUNNER_TEMP/csv-cmake"
+          curl --fail --location --retry 3 \
+            https://cmake.org/files/v3.31/cmake-3.31.6-linux-x86_64.tar.gz \
+            --output "$RUNNER_TEMP/csv-cmake.tar.gz"
+          echo "5a1133ff103c71eb5120e2cc3de922733e7d8a26a98ae716397e8676adb367bf  $RUNNER_TEMP/csv-cmake.tar.gz" | sha256sum --check
+          tar -xzf "$RUNNER_TEMP/csv-cmake.tar.gz" -C "$RUNNER_TEMP/csv-cmake" --strip-components=1
+          docker pull "$GCC_IMAGE"
+          docker run --rm "$GCC_IMAGE" g++ --version
+          test "$(docker run --rm "$GCC_IMAGE" g++ -dumpfullversion)" = "$GCC_VERSION"
+
+      - name: Build and run CMake library consumers
+        run: |
+          docker run --rm --user "$(id -u):$(id -g)" \
+            -v "$GITHUB_WORKSPACE:/src" -v "$RUNNER_TEMP/csv-cmake:/cmake:ro" \
+            -w /src "$GCC_IMAGE" bash -euc '
+              /cmake/bin/cmake -S tests/compatibility/gcc -B build/gcc-linked -DCMAKE_BUILD_TYPE=Release
+              /cmake/bin/cmake --build build/gcc-linked --parallel 2
+              /cmake/bin/ctest --test-dir build/gcc-linked --output-on-failure
+            '
+
+      - name: Build and run standalone generated header consumers
+        # Preserve independent diagnostics even if the linked-library check fails.
+        if: ${{ !cancelled() && steps.toolchain.outcome == 'success' }}
+        run: |
+          docker run --rm --user "$(id -u):$(id -g)" \
+            -v "$GITHUB_WORKSPACE:/src" -v "$RUNNER_TEMP/csv-cmake:/cmake:ro" \
+            -w /src "$GCC_IMAGE" bash -euc '
+              /cmake/bin/cmake -S tests/compatibility/gcc -B build/gcc-generated \
+                -DCMAKE_BUILD_TYPE=Release \
+                -DCSV_COMPAT_SINGLE_HEADER_DIR=/src/build/gcc-header/single_include_generated
+              /cmake/bin/cmake --build build/gcc-generated --parallel 2
+              /cmake/bin/ctest --test-dir build/gcc-generated --output-on-failure
+            '

.github/workflows/sanitizers.yml

@@ -9,7 +9,14 @@ on:
 permissions:
   contents: read
 
+# New PR commits supersede older checks; keep every non-PR run independent.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && format('pr-{0}', github.event.pull_request.number) || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 env:
+  # Bound compiler memory use while taking advantage of multiple runner cores.
+  CMAKE_BUILD_PARALLEL_LEVEL: "2"
   CSV_FETCHCONTENT_BASE_DIR: ${{ github.workspace }}/.cache/fetchcontent
 
 jobs:
@@ -54,11 +61,6 @@ jobs:
         path: ${{ env.CSV_FETCHCONTENT_BASE_DIR }}
         key: fetchcontent-${{ runner.os }}-sanitizer-${{ matrix.sanitizer }}-std${{ matrix.cxx_standard }}-${{ hashFiles('CMakeLists.txt', 'tests/CMakeLists.txt') }}
 
-    - name: Install dependencies
-      run: |
-        sudo apt-get update
-        sudo apt-get install -y build-essential cmake
-
     - name: Configure CMake with ${{ matrix.name }}
       run: |
         mkdir -p build

tests/CMakeLists.txt

@@ -4,6 +4,7 @@ FetchContent_Declare(
   Catch2
   GIT_REPOSITORY https://github.com/catchorg/Catch2.git
   GIT_TAG v3.6.0
+  GIT_SHALLOW TRUE
 ) 
 
 FetchContent_MakeAvailable(Catch2)

tests/compatibility/gcc/CMakeLists.txt

@@ -0,0 +1,34 @@
+cmake_minimum_required(VERSION 3.15)
+project(csv_gcc_compatibility LANGUAGES C CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+enable_testing()
+
+function(add_float_smoke name)
+    add_executable(${name} smoke.cpp)
+    add_test(NAME ${name} COMMAND ${name})
+endfunction()
+
+if(CSV_COMPAT_SINGLE_HEADER_DIR)
+    # Standalone consumers deliberately inherit no csv target definitions.
+    find_package(Threads REQUIRED)
+    foreach(name generated_float_smoke generated_float_optout)
+        add_float_smoke(${name})
+        target_include_directories(${name} PRIVATE "${CSV_COMPAT_SINGLE_HEADER_DIR}")
+        target_link_libraries(${name} PRIVATE Threads::Threads)
+    endforeach()
+    target_compile_definitions(generated_float_optout PRIVATE
+        CLASSIFY_SCALAR_DISABLE_STD_FLOAT_FROM_CHARS=1
+        CSV_COMPAT_EXPECT_FLOAT_OPTOUT=1)
+else()
+    set(CSV_BUILD_TESTS OFF CACHE BOOL "" FORCE)
+    set(CSV_BUILD_PROGRAMS OFF CACHE BOOL "" FORCE)
+    set(BUILD_PYTHON OFF CACHE BOOL "" FORCE)
+    add_subdirectory("${CMAKE_CURRENT_LIST_DIR}/../../.." csv-library)
+    foreach(library csv csv_no_simd)
+        add_float_smoke(${library}_float_smoke)
+        target_link_libraries(${library}_float_smoke PRIVATE ${library})
+    endforeach()
+endif()

tests/compatibility/gcc/smoke.cpp

@@ -0,0 +1,26 @@
+#include "csv.hpp"
+
+#include <cmath>
+#include <iostream>
+
+#if defined(CSV_COMPAT_EXPECT_FLOAT_OPTOUT) && defined(CLASSIFY_SCALAR_HAS_STD_FLOAT_FROM_CHARS)
+#error "The explicit floating-point from_chars opt-out was ignored"
+#endif
+
+int main() {
+    // Exercise field conversion and linking on old libstdc++ versions without
+    // involving reader/chunk behavior, which is covered by the main suite.
+    const char* inputs[] = { "1.25", "-42.5", "6.25e2", "1.5e-3" };
+    const double expected[] = { 1.25, -42.5, 625.0, 0.0015 };
+    for (unsigned i = 0; i < sizeof(inputs) / sizeof(inputs[0]); ++i) {
+        csv::CSVField field(inputs[i]);
+        const double actual = field.get<double>();
+        if (!field.is_float() || !std::isfinite(actual)
+            || std::abs(actual - expected[i]) > 1e-12) {
+            std::cerr << "Incorrect floating-point conversion for " << inputs[i]
+                      << ": " << actual << '\n';
+            return 1;
+        }
+    }
+    return 0;
+}