feat: support gcc-15 on Windows, macOS

Author: perazz

.github/compat/matrix.yml

@@ -6,6 +6,7 @@ os:
   - windows-2025
   - windows-2022
 toolchain:
+  - {compiler: gcc, version: 15}
   - {compiler: gcc, version: 14}
   - {compiler: gcc, version: 13}
   - {compiler: gcc, version: 12}
@@ -94,4 +95,9 @@ exclude:
   - os: windows-2025
     toolchain: {compiler: nvidia-hpc}
   - os: windows-2022
-    toolchain: {compiler: nvidia-hpc}
+    toolchain: {compiler: nvidia-hpc}
+  # gcc 15 only available for windows (via chocolatey), macos (brew)
+  - os: ubuntu-24.04
+    toolchain: {compiler: gcc, version: 15}
+  - os: ubuntu-22.04
+    toolchain: {compiler: gcc, version: 15}

setup-fortran.sh

@@ -116,9 +116,19 @@ install_gcc_choco()
       latest)
         choco install mingw --force
         ;;
+      15)
+        choco install mingw --version 15.2.0 --force
+        # mingw 13+ on Windows doesn't create shims (http://disq.us/p/2w5c5tj)
+        # so hide Strawberry compilers and manually add mingw bin dir to PATH
+        mkdir "$RUNNER_TEMP/strawberry"
+        mv /c/Strawberry/c/bin/gfortran "$RUNNER_TEMP/strawberry/gfortran"
+        mv /c/Strawberry/c/bin/gcc "$RUNNER_TEMP/strawberry/gcc"
+        mv /c/Strawberry/c/bin/g++ "$RUNNER_TEMP/strawberry/g++"
+        echo "C:\ProgramData\mingw64\mingw64\bin" >> $GITHUB_PATH
+        ;;
       13)
         choco install mingw --version 13.2.0 --force
-        # mingw 13 on Windows doesn't create shims (http://disq.us/p/2w5c5tj)
+        # mingw 13+ on Windows doesn't create shims (http://disq.us/p/2w5c5tj)
         # so hide Strawberry compilers and manually add mingw bin dir to PATH
         mkdir "$RUNNER_TEMP/strawberry"
         mv /c/Strawberry/c/bin/gfortran "$RUNNER_TEMP/strawberry/gfortran"
@@ -142,7 +152,7 @@ install_gcc_choco()
         choco install mingw --version 8.5.0 --force
         ;;
       *)
-        echo "Unsupported version: $version (choose 8-13 or latest)"
+        echo "Unsupported version: $version (choose 8-13, 15, or latest)"
         exit 1
         ;;
     esac