[CI] Split build dependencies into own job on Windows

.github/workflows/windows.yml

@@ -56,6 +56,7 @@
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
       crate-build-matrix: ${{ steps.set-matrix.outputs.crate-build-matrix }}
+      dep-build-matrix: ${{ steps.set-matrix.outputs.dep-build-matrix }}
       any_builds: ${{ steps.set-matrix.outputs.any_builds }}
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
@@ -97,6 +98,7 @@
           # Extract python-build matrix
           echo "matrix=$(jq -c '."python-build"' matrix.json)" >> $GITHUB_OUTPUT
           echo "crate-build-matrix=$(jq -c '."crate-build"' matrix.json)" >> $GITHUB_OUTPUT
+          echo "dep-build-matrix=$(jq -c '."deps-build"' matrix.json)" >> $GITHUB_OUTPUT
 
           # Display the matrix for debugging too
           cat matrix.json | jq
@@ -116,6 +118,7 @@
     needs:
       - generate-matrix
       - crate-build
+      - build-deps
     # Permissions used for actions/attest-build-provenance
     permissions:
       id-token: write
@@ -151,11 +154,18 @@
       - name: Bootstrap Python environment
         run: |
           uv run build.py --help
 
+      - name: Download build dependencies
+        uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0 # v5.0.0
+        with:
+          name: build-deps-${{ matrix.target_triple }}-${{ matrix.build_options}}
+          path: build
+
       - name: Build
         if: ${{ ! matrix.dry-run }}
         shell: cmd
         run: |
+          DIR
           IF "%MATRIX_VS_VERSION%"=="2026" (
             call "C:\Program Files\Microsoft Visual Studio\18\Enterprise\VC\Auxiliary\Build\%MATRIX_VCVARS%"
           ) ELSE (
@@ -185,3 +195,56 @@
         run: |
           $Dists = Resolve-Path -Path "dist/*.tar.zst" -Relative
           .\pythonbuild.exe validate-distribution --run $Dists
+
+  build-deps:
+    timeout-minutes: 90
+    needs:
+      - generate-matrix
+    # Permissions used for actions/attest-build-provenance
+    runs-on: ${{ matrix.runner }}
+    strategy:
+      matrix: ${{ fromJson(needs.generate-matrix.outputs.dep-build-matrix) }}
+      fail-fast: false
+    name: build-deps / ${{ matrix.target_triple }} / ${{ matrix.build_options }}
+    steps:
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+        with:
+          fetch-depth: 0
+          persist-credentials: false
+
+      - name: Install Cygwin Environment
+        uses: cygwin/cygwin-install-action@f2009323764960f80959895c7bc3bb30210afe4d # v6
+        with:
+          packages: autoconf automake libtool
+
+      - name: Set up uv
+        uses: astral-sh/setup-uv@1e862dfacbd1d6d858c55d9b792c756523627244 # v7.1.4
+        with:
+          enable-cache: false
+
+      # We need to do this before we activate the VC++ environment or else binary packages
+      # don't get compiled properly.
+      - name: Bootstrap Python environment
+        run: |
+          uv run build.py --help
+
+      - name: Build
+        if: ${{ ! matrix.dry-run }}
+        shell: cmd
+        run: |
+          IF "%MATRIX_VS_VERSION%"=="2026" (
+            call "C:\Program Files\Microsoft Visual Studio\18\Enterprise\VC\Auxiliary\Build\%MATRIX_VCVARS%"
+          ) ELSE (
+            call "C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Auxiliary\Build\%MATRIX_VCVARS%"
+          )
+          uv run build.py --only-deps --sh c:\cygwin\bin\sh.exe --options %MATRIX_BUILD_OPTIONS% --vs %MATRIX_VS_VERSION%
+        env:
+          MATRIX_VCVARS: ${{ matrix.vcvars }}
+          MATRIX_BUILD_OPTIONS: ${{ matrix.build_options }}
+          MATRIX_VS_VERSION: ${{ matrix.vs_version }}
+
+      - name: Upload Build Dependencies
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
+        with:
+          name: build-deps-${{ matrix.target_triple }}-${{ matrix.build_options }}
+          path: build/*.tar

ci-matrix.py

@@ -127,6 +127,30 @@ def generate_docker_matrix_entries(
     return matrix_entries
 
 
+def generate_deps_build_matrix_entries(
+    python_entries: list[dict[str, str]],
+    platform_filter: str | None = None,
+) -> list[dict[str, str]]:
+    """Generate matrix entries for deps builds based on python build matrix."""
+    include_keys = {
+        "arch",
+        "target_triple",
+        "platform",
+        "runner",
+        "build_options",
+        "vcvars",
+        "vs_version",
+    }
+    dep_build_pairs = set()
+    for entry in python_entries:
+        platform = entry["platform"]
+        if platform_filter and platform != platform_filter:
+            continue
+        pairs = tuple((k, v) for k, v in entry.items() if k in include_keys)
+        dep_build_pairs.add(pairs)
+    return [dict(pairs) for pairs in dep_build_pairs]
+
+
 def generate_crate_build_matrix_entries(
     python_entries: list[dict[str, str]],
     runners: dict[str, Any],
@@ -355,7 +379,7 @@ def parse_args() -> argparse.Namespace:
     )
     parser.add_argument(
         "--matrix-type",
-        choices=["python-build", "docker-build", "crate-build", "all"],
+        choices=["python-build", "docker-build", "crate-build", "deps-build", "all"],
         default="all",
         help="Which matrix types to generate (default: all)",
     )
@@ -443,6 +467,14 @@ def main() -> None:
         )
         result["crate-build"] = {"include": crate_entries}
 
+    # Generate deps-build matrix if requested
+    if args.matrix_type in ["deps-build", "all"]:
+        deps_entries = generate_deps_build_matrix_entries(
+            python_entries,
+            args.platform,
+        )
+        result["deps-build"] = {"include": deps_entries}
+
     print(json.dumps(result))
 
 

cpython-windows/build.py

@@ -1910,6 +1910,11 @@ def main() -> None:
         default="10.0.26100.0",
         help="Windows SDK version to build with",
     )
+    parser.add_argument(
+        "--only-deps",
+        action='store_true',
+        help="Build only dependencies, not CPython",
+    )
 
     args = parser.parse_args()
     build_options = args.options
@@ -1964,6 +1969,10 @@ def main() -> None:
                 libffi_archive,
             )
 
+        # Stop if only building dependencies
+        if args.only_deps:
+            return
+
         LOG_PREFIX[0] = "cpython"
         tar_path = build_cpython(
             args.python,