Breaking Change: Change @protobuf//bazel/flags:prefer_prebuilt_proto flag to True.

PiperOrigin-RevId: 871890409

Author: Rachel Goldfinger

.github/workflows/test_bazel.yml

@@ -30,11 +30,12 @@ jobs:
         bazelversion: [ '8.0.0' ]
         bzlmod: [ true, false ]
         toolchain_resolution:
-          # Default flags, uses from-source protoc
+          # Default flags, uses from prebuilt protoc
           - ""
-          # still uses from-source protoc unless 
-          # --@com_google_protobuf//bazel/flags:prefer_prebuilt_protoc is set
-          - "--incompatible_enable_proto_toolchain_resolution=true"
+          # Still uses prebuilt protoc
+          - "--incompatible_enable_proto_toolchain_resolution=false"
+          # Uses protoc from source.
+          - "--@com_google_protobuf//bazel/flags:prefer_prebuilt_protoc=false"
     runs-on: ${{ matrix.runner }}-latest
     name: ${{ matrix.continuous-only && inputs.continuous-prefix || '' }} Examples ${{ matrix.runner }} ${{ matrix.bazelversion }}${{ matrix.bzlmod && ' (bzlmod)' || '' }} ${{ matrix.toolchain_resolution && ' (toolchain resolution)' || '' }}
     steps:
@@ -78,8 +79,27 @@ jobs:
             cd examples;
             bazel build //... @com_google_protobuf-examples-with-hyphen//... $BAZEL_FLAGS --enable_bzlmod=${{ matrix.bzlmod }} --enable_workspace=${{ !matrix.bzlmod }} ${{ matrix.toolchain_resolution }};
 
-      - name: Prebuilt test
-        if: ${{ matrix.bzlmod && (!matrix.continuous-only || inputs.continuous-run) }}
+  prebuilt-protoc:
+    strategy:
+      fail-fast: false
+      matrix:
+        runner: [ ubuntu, windows, macos ]
+        bazelversion: [ '8.0.0' ]
+        bzlmod: [ true ]
+        toolchain_resolution:
+          # Default flags, uses from prebuilt protoc
+          - ""
+    runs-on: ${{ matrix.runner }}-latest
+    name: ${{ matrix.continuous-only && inputs.continuous-prefix || '' }} Prebuilt test ${{ matrix.runner }} ${{ matrix.bazelversion }} ${{ matrix.toolchain_resolution && ' (toolchain resolution)' || '' }}
+    steps:
+      - name: Checkout pending changes
+        if: ${{ !matrix.continuous-only || inputs.continuous-run }}
+        uses: protocolbuffers/protobuf-ci/checkout@v5
+        with:
+          ref: ${{ inputs.safe-checkout }}
+
+      - name: Run tests
+        if: ${{ !matrix.continuous-only || inputs.continuous-run }}
         uses: protocolbuffers/protobuf-ci/bazel@v5
         with:
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}

MODULE.bazel

@@ -120,8 +120,9 @@ use_repo(
     "prebuilt_protoc.win64",
 )
 
-# However this registration only matters if the config_setting for prefer_prebuilt_protoc is true,
-# using --@protobuf//bazel/flags:prefer_prebuilt_protoc
+# This registration applies when the config_setting for prefer_prebuilt_protoc is true.
+# This is now enabled by default.
+# It can be disabled using --@protobuf//bazel/flags:prefer_prebuilt_protoc=false
 register_toolchains("//bazel/private/oss/toolchains/prebuilt:all")
 
 # From-source protobuf toolchains

bazel/flags/BUILD

@@ -37,10 +37,10 @@ label_flag(
 )
 
 # When set to true, we will use a prebuilt protoc binary from GitHub if it's available.
+# This is now enabled by default.
 bool_flag(
     name = "prefer_prebuilt_protoc",
-    # TODO: this should be True after the feature is vetted with some adoption
-    build_setting_default = False,
+    build_setting_default = True,
     visibility = ["//bazel/toolchains:__pkg__"],
 )
 

bazel/tests/cc_toolchain_tests.bzl

@@ -18,12 +18,12 @@ def cc_toolchain_test_suite(name):
     test_suite(
         name = name,
         tests = [
-            _test_cc_toolchain_uses_full_protoc_when_prefer_prebuilt_flag_set,
-            _test_cc_toolchain_uses_protoc_minimal_by_default,
+            _test_cc_toolchain_uses_protoc_minimal_when_prefer_prebuilt_flag_unset,
+            _test_cc_toolchain_uses_full_protoc_by_default,
         ],
     )
 
-def _test_cc_toolchain_uses_full_protoc_when_prefer_prebuilt_flag_set(name):
+def _test_cc_toolchain_uses_protoc_minimal_when_prefer_prebuilt_flag_unset(name):
     util.helper_target(
         proto_library,
         name = name + "_proto",
@@ -39,21 +39,19 @@ def _test_cc_toolchain_uses_full_protoc_when_prefer_prebuilt_flag_set(name):
     analysis_test(
         name = name,
         target = name + "_compile",
-        impl = _test_cc_toolchain_uses_full_protoc_when_prefer_prebuilt_flag_set_impl,
-        config_settings = {_PREFER_PREBUILT_PROTOC: True},
+        impl = _test_cc_toolchain_uses_protoc_minimal_when_prefer_prebuilt_flag_unset_impl,
+        config_settings = {_PREFER_PREBUILT_PROTOC: False},
     )
 
-def _test_cc_toolchain_uses_full_protoc_when_prefer_prebuilt_flag_set_impl(env, target):
+def _test_cc_toolchain_uses_protoc_minimal_when_prefer_prebuilt_flag_unset_impl(env, target):
     # Find the compile action
     action = env.expect.that_target(target).action_named("GenProto")
 
-    # When prefer_prebuilt_protoc is True, protoc_minimal_do_not_use is None,
-    # so the cc_toolchain should use the full protoc (not protoc_minimal).
-    # The protoc path should end with "/protoc" not contain "protoc_minimal"
-    action.argv().contains_predicate(matching.str_matches("*/protoc"))
-    action.argv().not_contains_predicate(matching.str_matches("*protoc_minimal*"))
+    # When prefer_prebuilt_protoc is False, protoc_minimal_do_not_use is set,
+    # so the cc_toolchain should use protoc_minimal.
+    action.argv().contains_predicate(matching.str_matches("*protoc_minimal*"))
 
-def _test_cc_toolchain_uses_protoc_minimal_by_default(name):
+def _test_cc_toolchain_uses_full_protoc_by_default(name):
     util.helper_target(
         proto_library,
         name = name + "_proto",
@@ -69,13 +67,15 @@ def _test_cc_toolchain_uses_protoc_minimal_by_default(name):
     analysis_test(
         name = name,
         target = name + "_compile",
-        impl = _test_cc_toolchain_uses_protoc_minimal_by_default_impl,
+        impl = _test_cc_toolchain_uses_full_protoc_by_default_impl,
     )
 
-def _test_cc_toolchain_uses_protoc_minimal_by_default_impl(env, target):
+def _test_cc_toolchain_uses_full_protoc_by_default_impl(env, target):
     # Find the compile action
     action = env.expect.that_target(target).action_named("GenProto")
 
-    # By default (prefer_prebuilt_protoc is False), protoc_minimal_do_not_use is set,
-    # so the cc_toolchain should use protoc_minimal.
-    action.argv().contains_predicate(matching.str_matches("*protoc_minimal*"))
+    # By default (prefer_prebuilt_protoc is True), protoc_minimal_do_not_use is None,
+    # so the cc_toolchain should use the full protoc (not protoc_minimal).
+    # The protoc path should end with "/protoc" not contain "protoc_minimal"
+    action.argv().contains_predicate(matching.str_matches("*/protoc"))
+    action.argv().not_contains_predicate(matching.str_matches("*protoc_minimal*"))