[build] Disable WebGPU for Windows non-release builds

The Windows build is currently much slower than the macOS/Linux builds on CI,
especially on mostly cached builds.
Based on profiling on #2981, this is caused by the repo mapping stage for dawn
taking several minutes of Windows. Disable the experimental WebGPU feature on
Windows to better meet compile time constraints. Release builds remain
unaffected.
Fetching WPT also contributes here. Only fetch/use WPT on Unix and only
configure targets based on globs as we start using them, Bazel configures
90,000 targets for it otherwise.

.bazelrc

@@ -26,8 +26,13 @@ import %workspace%/build/ci.bazelrc
 
 import %workspace%/build/lint.bazelrc
 
-# Enable webgpu
-build --//src/workerd/io:enable_experimental_webgpu=True
+# Enable webgpu. Merely fetching the required Dawn library and computing the repo mapping based on
+# it slows down the Windows build significantly, so only enable this on Unix and for Windows release
+# builds. This is mostly motivated by compile time constraints, we hope to lift this limitation
+# again if this Windows performance bottleneck gets fixed within Bazel.
+build:unix --config=webgpu
+build:release_windows --config=webgpu
+build:webgpu --//src/workerd/io:enable_experimental_webgpu=True
 
 # Avoid generating duplicate runfile trees. This will become the default in a future bazel version.
 build --nolegacy_external_runfiles
@@ -38,16 +43,16 @@ build --incompatible_disallow_empty_glob
 # Prevents bazel cache invalidation when switching terminals
 build --incompatible_strict_action_env
 
-# Dawn tint build flags
-build --@dawn//src/tint:tint_build_glsl_writer=False
-build --@dawn//src/tint:tint_build_glsl_validator=False
-build --@dawn//src/tint:tint_build_hlsl_writer=True
-build --@dawn//src/tint:tint_build_ir=False
-build --@dawn//src/tint:tint_build_msl_writer=True
-build --@dawn//src/tint:tint_build_spv_reader=False
-build --@dawn//src/tint:tint_build_spv_writer=True
-build --@dawn//src/tint:tint_build_wgsl_reader=True
-build --@dawn//src/tint:tint_build_wgsl_writer=True
+# Dawn tint build flags. Only enable when building with webgpu support
+build:webgpu --@dawn//src/tint:tint_build_glsl_writer=False
+build:webgpu --@dawn//src/tint:tint_build_glsl_validator=False
+build:webgpu --@dawn//src/tint:tint_build_hlsl_writer=True
+build:webgpu --@dawn//src/tint:tint_build_ir=False
+build:webgpu --@dawn//src/tint:tint_build_msl_writer=True
+build:webgpu --@dawn//src/tint:tint_build_spv_reader=False
+build:webgpu --@dawn//src/tint:tint_build_spv_writer=True
+build:webgpu --@dawn//src/tint:tint_build_wgsl_reader=True
+build:webgpu --@dawn//src/tint:tint_build_wgsl_writer=True
 
 # Our dependencies (ICU, zlib, etc.) produce a lot of these warnings, so we disable them. Depending
 # on the clang version, zlib either produces warnings for -Wdeprecated-non-prototype or does not

build/BUILD.wpt

@@ -2,16 +2,11 @@
 # Licensed under the Apache 2.0 license found in the LICENSE file or at:
 #     https://opensource.org/licenses/Apache-2.0
 
-directories = glob(
-    ["*"],
-    exclude = glob(
-        ["*"],
-        exclude_directories = 1,
-    ) + [
-        ".*",
-    ],
-    exclude_directories = 0,
-)
+# successively enable wpt targets
+directories = [
+    "url",
+    "urlpattern",
+]
 
 [filegroup(
     name = dir,

build/ci.bazelrc

@@ -19,6 +19,12 @@ build:ci --color=yes
 # Indicate support for more terminal columns, 100 is the line length recommended by KJ style.
 build:ci --terminal_columns=100
 
+# Only build runfile trees when needed/lazily, so that they are not built for disabled tests
+build:ci --nobuild_runfile_links
+# Speeds up CI build by making action output uploads non-blocking so Bazel can e.g. run a test
+# before it finishes uploading the test binary. On-by-default in Bazel 8.
+build:ci --experimental_remote_cache_async
+
 build:ci --config=v8-codegen-opt
 test:ci --test_output=errors
 build:ci --disk_cache=~/bazel-disk-cache

build/wpt_test.bzl

@@ -16,6 +16,10 @@ def wpt_test(name, wpt_directory, test_js):
         test_name = name,
         wpt_directory = wpt_directory,
         test_js = test_js,
+        target_compatible_with = select({
+            "@platforms//os:windows": ["@platforms//:incompatible"],
+            "//conditions:default": [],
+        }),
     )
 
     wd_test(
@@ -28,6 +32,11 @@ def wpt_test(name, wpt_directory, test_js):
             wpt_directory,
             "//src/workerd/io:trimmed-supported-compatibility-date.txt",
         ],
+        # Even generating WPT tests is prohibitively expensive on Windows, disable it there
+        target_compatible_with = select({
+            "@platforms//os:windows": ["@platforms//:incompatible"],
+            "//conditions:default": [],
+        }),
     )
 
 def _wpt_test_gen_impl(ctx):

src/wpt/BUILD.bazel

@@ -1,8 +1,7 @@
 filegroup(
     name = "wpt-test-harness",
     srcs = glob(
-        include = ["**/*"],
-        allow_empty = True,
+        include = ["*.js"],
     ),
     visibility = ["//visibility:public"],
 )