Attempt to speed up Windows CI

.github/workflows/ci_windows.yml

@@ -9,22 +9,49 @@ jobs:
   build_and_test:
     runs-on: windows-latest
     timeout-minutes: 20
+    env:
+      BAZELISK_HOME: ${{ github.workspace }}\.bazel-cache\bazelisk
+      BAZEL_DISK_CACHE: ${{ github.workspace }}\.bazel-cache\disk
+      BAZEL_PROFILE_JSON: ${{ github.workspace }}\windows-fastbuild-profile.json.gz
+      WINDOWS_FASTBUILD_TARGETS: >-
+        //library/... //examples/... //python/... //jni/...
+      WINDOWS_OPT_TARGETS: >-
+        //library/src:dds //examples:analyse_play_pbn
     steps:
       # Checkout the repository
       - name: Checkout repository
         uses: actions/checkout@v6
 
+      # Reuse downloaded Bazel binaries across workflow runs
+      - name: Restore Bazelisk cache
+        uses: actions/cache@v4
+        with:
+          path: ${{ env.BAZELISK_HOME }}
+          key: windows-bazelisk-cache-${{ runner.os }}-${{ hashFiles('.bazelversion') }}
+          restore-keys: |
+            windows-bazelisk-cache-${{ runner.os }}-
+
       # Install Bazelisk (recommended Bazel launcher)
       - name: Setup Bazelisk
         uses: ./.github/actions/setup-bazelisk
 
-      # Warm external deps (emsdk, LLVM, …); retry transient network fetch failures
+      # Reuse compiled/action cache artifacts across workflow runs
+      - name: Restore Bazel disk cache
+        uses: actions/cache@v4
+        with:
+          path: ${{ github.workspace }}\.bazel-cache\disk
+          key: windows-bazel-disk-cache-${{ runner.os }}-${{ hashFiles('.bazelversion', '.bazelrc', 'MODULE.bazel', 'MODULE.bazel.lock', 'BUILD.bazel', 'CPPVARIABLES.bzl') }}
+          restore-keys: |
+            windows-bazel-disk-cache-${{ runner.os }}-
+
+      # Warm external deps for the same scope tested on Windows
       - name: Prefetch external repos
         shell: pwsh
         run: |
+          [string[]]$fastbuild_targets = $env:WINDOWS_FASTBUILD_TARGETS -split '\s+' | Where-Object { $_ -ne '' }
           $max = 3
           for ($i = 1; $i -le $max; $i++) {
-            bazelisk fetch //...
+            bazelisk fetch --disk_cache="$env:BAZEL_DISK_CACHE" --verbose_failures @fastbuild_targets
             if ($LASTEXITCODE -eq 0) { exit 0 }
             if ($i -lt $max) {
               Write-Host "Fetch failed (attempt $i/$max). Retrying in 20s..."
@@ -33,15 +60,21 @@ jobs:
           }
           exit 1
 
-      # Build all targets (retry: fetch flakes can still surface on first analysis).
-      # --config=opt: DDS_CPPOPTS no longer forces /O2 (that fought Bazel's /Od and
-      # triggered MSVC D9025); opt mode is how Windows keeps release-level codegen.
-      - name: Bazel build (retry on transient fetch failure)
+      # Run Windows-native coverage in fastbuild (test-centric flow)
+      - name: Run Windows test targets
+        shell: pwsh
+        run: |
+          [string[]]$fastbuild_targets = $env:WINDOWS_FASTBUILD_TARGETS -split '\s+' | Where-Object { $_ -ne '' }
+          bazelisk test --disk_cache="$env:BAZEL_DISK_CACHE" --profile="$env:BAZEL_PROFILE_JSON" --verbose_failures @fastbuild_targets
+
+      # Keep a narrow release-level check on Windows with --config=opt
+      - name: Build Windows opt smoke targets (retry on transient fetch failure)
         shell: pwsh
         run: |
+          [string[]]$opt_targets = $env:WINDOWS_OPT_TARGETS -split '\s+' | Where-Object { $_ -ne '' }
           $max = 3
           for ($i = 1; $i -le $max; $i++) {
-            bazelisk build --config=opt --verbose_failures //...
+            bazelisk build --config=opt --disk_cache="$env:BAZEL_DISK_CACHE" --verbose_failures @opt_targets
             if ($LASTEXITCODE -eq 0) { exit 0 }
             if ($i -lt $max) {
               Write-Host "Build failed (attempt $i/$max). Retrying in 20s..."
@@ -52,10 +85,6 @@ jobs:
           }
           exit 1
 
-      # Run all tests (including Python) — no retry so real test failures surface quickly
-      - name: Run all tests
-        run: bazelisk test --config=opt --verbose_failures //...
-
       # Upload test logs
       - name: Upload test logs - Windows
         if: always()
@@ -65,3 +94,14 @@ jobs:
           path: bazel-testlogs/
           if-no-files-found: ignore
           retention-days: 30
+
+      # Upload profile artifacts
+      - name: Upload Bazel profile - Windows
+        if: always()
+        uses: actions/upload-artifact@v6
+        with:
+          name: bazel-profile-windows
+          path: |
+            ${{ github.workspace }}\windows-fastbuild-profile.json.gz
+          if-no-files-found: ignore
+          retention-days: 30

python/tests/ci_windows_cppopts_test.py

@@ -67,6 +67,10 @@ def _bazelisk_invocation_has_config_opt(text: str, subcommand: str) -> bool:
     return False
 
 
+def _workflow_lines_with(text: str, needle: str) -> list[str]:
+    return [line for line in text.splitlines() if needle in line]
+
+
 class TestWindowsMsvcCppoptsAvoidD9025(unittest.TestCase):
     def test_windows_cppopts_do_not_override_bazel_optimization(self) -> None:
         """Bazel already sets /Od (fastbuild/dbg) or /O2 (opt); re-stating any
@@ -360,17 +364,36 @@ def test_matches_when_config_opt_precedes_trailing_comment(self) -> None:
 
 class TestWindowsCiUsesOpt(unittest.TestCase):
     def test_windows_ci_passes_config_opt(self) -> None:
-        """Without /O2 in DDS_CPPOPTS, CI must opt in via --config=opt."""
+        """Windows CI keeps opt only for a focused release validation step."""
         text = (
             _repo_root() / ".github" / "workflows" / "ci_windows.yml"
         ).read_text(encoding="utf-8")
+        self.assertFalse(
+            _bazelisk_invocation_has_config_opt(text, "test"),
+            "expected broad Windows test coverage to run in fastbuild",
+        )
         self.assertTrue(
             _bazelisk_invocation_has_config_opt(text, "build"),
-            "expected Windows CI build to use --config=opt",
+            "expected a focused Windows build step to keep --config=opt",
         )
+
+    def test_windows_ci_limits_scope_and_collects_profile(self) -> None:
+        text = (
+            _repo_root() / ".github" / "workflows" / "ci_windows.yml"
+        ).read_text(encoding="utf-8")
+        self.assertIn("WINDOWS_FASTBUILD_TARGETS", text)
+        self.assertNotIn("bazelisk fetch //...", text)
+        self.assertNotIn("bazelisk test --verbose_failures //...", text)
+        self.assertNotIn("bazelisk build --config=opt --verbose_failures //...", text)
+        self.assertRegex(
+            text,
+            r"actions/cache@v4",
+            "expected Windows workflow to enable cross-run Bazel caching",
+        )
+        test_lines = _workflow_lines_with(text, "bazelisk test")
         self.assertTrue(
-            _bazelisk_invocation_has_config_opt(text, "test"),
-            "expected Windows CI test to use --config=opt",
+            any("--profile=" in line for line in test_lines),
+            "expected Windows test command to emit a Bazel profile",
         )