Use native.proto_library for Bazel 7 and explicitly error for Bazel 6 which is incompatible and out of support.

zhangskz · copybara-github · commit da0077eb6289 · 2025-05-23T14:38:02.000-07:00
Reduces skew caused by Bazel 7 using bazel's cc_proto_library, protobuf's proto_library, and bazel's proto info which block changes e.g. cl/743679882

Pins `rules_proto` to `7.1.0` to avoid `Protocol compiler toolchain could not be resolved.` when `--incompatible_toolchain_resolution`. MODULE.bazel otherwise defaults to `rules_proto 7.0.2` (from other deps) which inconsistently uses bazel's toolchain_type but protobuf's toolchain. WORKSPACE otherwise defaults to `rules_proto 5.3.0-21.7` (from bazel) where `@rules_proto//proto:toolchain_type` referenced by Bazel 7 doesn't exist yet.

The final state is that toolchains from protobuf are used, instead of @rules_proto which forwards to protobuf after `rules_proto 6.0.0` to avoid breaking change requiring users to register toolchains from `rules_proto` for Bazel 7.

PiperOrigin-RevId: 762571203
diff --git a/.github/workflows/test_bazel.yml b/.github/workflows/test_bazel.yml
@@ -67,7 +67,7 @@ jobs:
         uses: protocolbuffers/protobuf-ci/bazel@v4
         with:
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
-          bazel-cache: examples
+          bazel-cache: examples-${{ matrix.bazelversion }}-${{ matrix.bzlmod }}-${{ matrix.toolchain_resolution }}
           version: ${{ matrix.bazelversion }}
           bash: >
             cd examples;
diff --git a/MODULE.bazel b/MODULE.bazel
@@ -46,6 +46,14 @@ bazel_dep(name = "rules_license", version = "1.0.0")
 bazel_dep(name = "rules_pkg", version = "1.0.1")
 bazel_dep(name = "rules_python", version = "1.0.0")
 
+# Pin to rules_proto to 7.1.0 to avoid toolchain incompatibilities when
+# --incompatible_enable_proto_toolchain_resolution=true in Bazel 7.
+# rules_proto 7.0.2 from deps incorrectly rules_proto's toolchain_type but protobuf's toolchain, but
+# 7.1.0 uses protobuf's toolchain and toolchain_type.
+# TODO: Restore to dev_dependency once Bazel 7 is dropped.
+# rules_proto is needed for @com_google_protobuf_v25 used in //compatibility/... tests
+bazel_dep(name = "rules_proto", version = "7.1.0")
+
 bazel_dep(name = "rules_rust", version = "0.56.0", dev_dependency = True)
 bazel_dep(name = "rules_ruby", version = "0.17.3", dev_dependency = True)
 
@@ -82,6 +90,7 @@ ruby.toolchain(
     version = "system",
 )
 use_repo(ruby, "ruby")
+
 ruby.bundle_fetch(
     name = "protobuf_bundle",
     gem_checksums = {
@@ -227,9 +236,6 @@ bazel_dep(
 cc_configure = use_extension("@rules_cc//cc:extensions.bzl", "cc_configure_extension")
 use_repo(cc_configure, "local_config_cc")
 
-# rules_proto are needed for @com_google_protobuf_v25 used in //compatibility/... tests
-bazel_dep(name = "rules_proto", version = "7.0.2", dev_dependency = True)
-
 # For the Lua upb implementation
 bazel_dep(name = "lua", version = "5.4.6", dev_dependency = True)
 
diff --git a/bazel/proto_library.bzl b/bazel/proto_library.bzl
@@ -11,8 +11,12 @@ load("@proto_bazel_features//:features.bzl", "bazel_features")
 load("//bazel/private:proto_library_rule.bzl", _proto_library = "proto_library")
 
 def proto_library(**kwattrs):
-    # This condition causes Starlark rules to be used only on Bazel >=7.0.0
-    if bazel_features.proto.starlark_proto_info:
+    # Bazel 6 predates Starlark ProtoInfo and is not compatible with Starklark proto_library.
+    if not bazel_features.proto.starlark_proto_info:
+        fail("Protobuf proto_library is not compatible with Bazel 6.")
+
+    # Only use Starlark rules when they are removed from Bazel.
+    if not hasattr(native, "proto_library"):
         _proto_library(**kwattrs)
     else:
         # On older Bazel versions keep using native rules, so that mismatch in ProtoInfo doesn't happen
diff --git a/protobuf_deps.bzl b/protobuf_deps.bzl
@@ -53,6 +53,16 @@ def _github_archive(repo, commit, **kwargs):
 def protobuf_deps():
     """Loads common dependencies needed to compile the protobuf library."""
 
+    # Pin rules_proto since Bazel 7 otherwise depends on rules_proto 5.3.0-21.7 which is missing
+    # @rules_proto//proto:toolchain_type used by Bazel.
+    # 6.0.0 would at least require users to add `register_toolchains` for rules_proto
+    # TODO: Remove once Bazel 7 is no longer supported.
+    if not native.existing_rule("rules_proto"):
+        http_archive(
+            name = "rules_proto",
+            strip_prefix = "rules_proto-7.1.0",
+            url = "https://github.com/bazelbuild/rules_proto/releases/download/7.1.0/rules_proto-7.1.0.tar.gz",
+        )
     if not native.existing_rule("bazel_features"):
         http_archive(
             name = "bazel_features",
