ci: add Windows Fortran

.github/workflows/ci.yml

@@ -30,14 +30,20 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - uses: awvwgk/setup-fortran@main
+    - uses: fortran-lang/setup-fortran@v1
       id: setup-fortran
-      if: runner.os != 'Windows'
-      # We aren't using this yet, and takes 4 mins to setup on Windows
-      # On macOS this causes a bug to be hit on macos-13+ and CMake, gcc14 may fix
       with:
         compiler: gcc
         version: 12
+    # setup-fortran installs MinGW via choco, which only edits the machine PATH
+    # registry; GitHub Actions doesn't reload that into the running job. Put the
+    # bin dir on PATH so CMake can find gcc/gfortran (see pi-fortran override).
+    - name: Add MinGW to PATH (Windows)
+      if: runner.os == 'Windows'
+      shell: pwsh
+      run: |
+        $bin = Split-Path (Get-ChildItem C:\ProgramData\chocolatey\lib\mingw -Recurse -Filter gfortran.exe | Select-Object -First 1).FullName
+        "$bin" | Out-File -FilePath $env:GITHUB_PATH -Append -Encoding utf8
     - uses: astral-sh/setup-uv@v8.0.0
     - run: uvx nox -s ${{ matrix.session }}
 

noxfile.py

@@ -11,9 +11,8 @@
     "hello-pybind11",
     "hello-cython",
     "hello-cmake-package",
+    "pi-fortran",
 ]
-if not sys.platform.startswith("win"):
-    hello_list.append("pi-fortran")
 long_hello_list = [
     *hello_list,
     "pen2-cython",

projects/pi-fortran/CMakeLists.txt

@@ -15,6 +15,8 @@ execute_process(
   OUTPUT_VARIABLE F2PY_INCLUDE_DIR
   OUTPUT_STRIP_TRAILING_WHITESPACE
 )
+# On Windows the path comes back with backslashes, which CMake reads as escapes.
+file(TO_CMAKE_PATH "${F2PY_INCLUDE_DIR}" F2PY_INCLUDE_DIR)
 
 set(f2py_module_name "pi")
 set(fortran_src_file "${CMAKE_SOURCE_DIR}/pi/_pi.f")
@@ -41,4 +43,10 @@ target_include_directories(${CMAKE_PROJECT_NAME} PUBLIC
 
 target_link_libraries(${CMAKE_PROJECT_NAME} PUBLIC Python::NumPy)
 
+# With the MinGW toolchain (Windows), statically link the GNU runtime so the
+# module has no external libgfortran/libgcc/libwinpthread DLL dependencies.
+if(WIN32 AND CMAKE_Fortran_COMPILER_ID STREQUAL "GNU")
+  target_link_options(${CMAKE_PROJECT_NAME} PRIVATE -static)
+endif()
+
 install(TARGETS ${CMAKE_PROJECT_NAME} DESTINATION pi)

projects/pi-fortran/pyproject.toml

@@ -14,3 +14,12 @@ dependencies = ["numpy>=1.21"]
 [tool.scikit-build]
 ninja.version = ">=1.10"
 cmake.version = ">=3.17.2"
+
+# Windows defaults to the Visual Studio generator, which has no Fortran support
+# and ignores compiler overrides. Use Ninja with the MinGW toolchain instead
+# (gcc and gfortran must be on PATH).
+[[tool.scikit-build.overrides]]
+if.platform-system = "win32"
+cmake.args = ["-GNinja"]
+cmake.define.CMAKE_C_COMPILER = "gcc"
+cmake.define.CMAKE_Fortran_COMPILER = "gfortran"