Add gcc 15 to CI

.github/workflows/cmake.yml

@@ -14,6 +14,8 @@ jobs:
     # See: https://docs.github.com/en/actions/configuring-and-managing-workflows/configuring-a-workflow#configuring-a-build-matrix
     name: ${{ matrix.config.name }}
     runs-on: ${{ matrix.config.os }}
+    # Allow specifying a container per-matrix to avoid duplicating jobs
+    container: ${{ matrix.config.container }}
 
     strategy:
       fail-fast: false
@@ -103,6 +105,22 @@ jobs:
             cxx: "g++-14",
             cxxver: 20,
           }
+          - {
+            name: "Linux g++ 15 (Debian) C++17",
+            os: ubuntu-24.04,
+            container: debian:testing,
+            buildtype: Release,
+            cxx: "g++-15",
+            cxxver: 17,
+          }
+          - {
+            name: "Linux g++ 15 (Debian) C++20",
+            os: ubuntu-24.04,
+            container: debian:testing,
+            buildtype: Release,
+            cxx: "g++-15",
+            cxxver: 20,
+          }
           - {
             name: "Linux clang-13 C++17",
             os: ubuntu-22.04,
@@ -472,6 +490,14 @@ jobs:
         sudo add-apt-repository ppa:ubuntu-toolchain-r/ppa
         sudo apt-get install g++-14
 
+    - name: Install GCC 15 and tools (Debian container)
+      if: matrix.config.container == 'debian:testing' && matrix.config.cxx == 'g++-15'
+      shell: bash
+      run: |
+        apt-get update
+        DEBIAN_FRONTEND=noninteractive apt-get install -y \
+          g++-15 cmake ninja-build build-essential pkg-config
+
     - name: Install MSVC 2017
       id: install_msvc_2017
       if: startsWith(matrix.config.os, 'windows-2019') && ( matrix.config.cxx == 'cl' ) && ( matrix.config.msvcver == 2017 )
@@ -501,14 +527,14 @@ jobs:
     - name: Create Build Environment
       # Some projects don't allow in-source building, so create a separate build directory
       # We'll use this as our working directory for all subsequent commands
-      run: cmake -E make_directory ${{runner.workspace}}/build
+      run: cmake -E make_directory "build"
 
     - name: Configure CMake
       if: (!contains(matrix.config.mingw, 'MINGW'))
       # Use a bash shell so we can use the same syntax for environment variable
       # access regardless of the host operating system
       shell: bash
-      working-directory: ${{runner.workspace}}/build
+      working-directory: build
       env: 
         CXX: ${{ matrix.config.cxx }}
       # Note the current convention is to use the -S and -B options here to specify source 
@@ -528,15 +554,16 @@ jobs:
 
     - name: Build
       if: (!contains(matrix.config.mingw, 'MINGW'))
-      working-directory: ${{runner.workspace}}/build
+      working-directory: build
       shell: bash
       # Execute the build.  You can specify a specific target with "--target <NAME>"
       run: cmake --build . --config ${{ matrix.config.buildtype }}
 
     - name: Test
       if: (!contains(matrix.config.mingw, 'MINGW'))
-      working-directory: ${{runner.workspace}}/build
+      working-directory: build
       shell: bash
       # Execute tests defined by the CMake configuration.  
       # See https://cmake.org/cmake/help/latest/manual/ctest.1.html for more detail
       run: ctest --output-on-failure -C ${{ matrix.config.buildtype }}
+