Add breaking change detection for well-known types (#17513)

Adds new tests in `//compatibility` for detecting undesired breaking changes in the schema of the well-known types and `descriptor.proto` files, using the Buf breaking change detector, via [`rules_buf`](https://github.com/bufbuild/rules_buf/).

In order to keep things light-touch as far as maintenance goes, I have chosen to keep the integration as small and simple as possible. Some notes:

- Breaking change behavior can be granularly controlled via [`buf.yaml`](https://buf.build/docs/configuration/v1/buf-yaml#breaking).

- Bazel sandboxes us away from meaningful VCS information, so in order to pick a target to check for breaking changes against, a new variable is added to `protobuf_versions.bzl` that needs to be updated with changes in the release version.

- Breaking change detection is performed on a file-level, not a package-level, so migrating types across WKT files would constitute a breaking change. If this is not desired the behavior can be made to work on a package-level, though we need to do some more work as `buf_breaking_test` currently only accepts a single file descriptor set target for the `against` attribute.

Closes #17513

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/17513 from jchadwick-buf:buf-breaking cd46bb2c1e
PiperOrigin-RevId: 658624708

MODULE.bazel

@@ -95,6 +95,7 @@ use_repo(maven, "maven")
 
 # Development dependencies
 bazel_dep(name = "googletest", version = "1.14.0", repo_name = "com_google_googletest", dev_dependency = True)
+bazel_dep(name = "rules_buf", version = "0.3.0", dev_dependency = True)
 bazel_dep(name = "rules_testing", version = "0.6.0", dev_dependency = True)
 # rules_proto are needed for @com_google_protobuf_v25.0 used in //compatibility/... tests
-bazel_dep(name = "rules_proto", version = "4.0.0", dev_dependency = True)
+bazel_dep(name = "rules_proto", version = "4.0.0", dev_dependency = True)

WORKSPACE

@@ -254,3 +254,27 @@ http_archive(
     strip_prefix = "rules_testing-0.6.0",
     url = "https://github.com/bazelbuild/rules_testing/releases/download/v0.6.0/rules_testing-v0.6.0.tar.gz",
 )
+
+# For checking breaking changes to well-known types from the previous release version.
+load("//:protobuf_version.bzl", "PROTOBUF_PREVIOUS_RELEASE")
+
+http_archive(
+    name = "com_google_protobuf_previous_release",
+    strip_prefix = "protobuf-" + PROTOBUF_PREVIOUS_RELEASE,
+    url = "https://github.com/protocolbuffers/protobuf/releases/download/v{0}/protobuf-{0}.tar.gz".format(PROTOBUF_PREVIOUS_RELEASE),
+)
+
+http_archive(
+    name = "rules_buf",
+    integrity = "sha256-Hr64Q/CaYr0E3ptAjEOgdZd1yc+cBjp7OG1wzuf3DIs=",
+    strip_prefix = "rules_buf-0.3.0",
+    urls = [
+        "https://github.com/bufbuild/rules_buf/archive/refs/tags/v0.3.0.zip",
+    ],
+)
+
+load("@rules_buf//buf:repositories.bzl", "rules_buf_dependencies", "rules_buf_toolchains")
+
+rules_buf_dependencies()
+
+rules_buf_toolchains(version = "v1.32.1")

WORKSPACE.bzlmod

@@ -38,3 +38,11 @@ http_archive(
     url = "https://github.com/protocolbuffers/utf8_range/archive/d863bc33e15cba6d873c878dcca9e6fe52b2f8cb.zip",
 )
 
+# Needed for checking breaking changes from the previous release version.
+load("//:protobuf_version.bzl", "PROTOBUF_PREVIOUS_RELEASE")
+
+http_archive(
+    name = "com_google_protobuf_previous_release",
+    strip_prefix = "protobuf-" + PROTOBUF_PREVIOUS_RELEASE,
+    url = "https://github.com/protocolbuffers/protobuf/releases/download/v{0}/protobuf-{0}.tar.gz".format(PROTOBUF_PREVIOUS_RELEASE),
+)

compatibility/BUILD.bazel

@@ -1,11 +1,12 @@
+load("@rules_buf//buf:defs.bzl", "buf_breaking_test")
+load("//compatibility:runtime_conformance.bzl", "java_runtime_conformance")
+
 # Simple build tests for compatibility of gencode from previous major versions
 # with the current runtime.
 #
 # To add more test cases in Java, use java_runtime_conformance as below, and add
 # the corresponding http_archive in the WORKSPACE file for the version.
 
-load("//compatibility:runtime_conformance.bzl", "java_runtime_conformance")
-
 # main gencode builds with main runtime as a proof of concept.
 java_runtime_conformance(
     name = "java_conformance_main",
@@ -17,3 +18,122 @@ java_runtime_conformance(
     name = "java_conformance_v3.25.0",
     gencode_version = "3.25.0",
 )
+
+# Breaking change detection for well-known types and descriptor.proto.
+buf_breaking_test(
+    name = "any_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:any_proto",
+    config = ":buf.yaml",
+    targets = ["//:any_proto"],
+)
+
+buf_breaking_test(
+    name = "api_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:api_proto",
+    config = ":buf.yaml",
+    targets = ["//:api_proto"],
+)
+
+buf_breaking_test(
+    name = "descriptor_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:descriptor_proto",
+    config = ":buf.yaml",
+    targets = ["//:descriptor_proto"],
+)
+
+buf_breaking_test(
+    name = "duration_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:duration_proto",
+    config = ":buf.yaml",
+    targets = ["//:duration_proto"],
+)
+
+buf_breaking_test(
+    name = "empty_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:empty_proto",
+    config = ":buf.yaml",
+    targets = ["//:empty_proto"],
+)
+
+buf_breaking_test(
+    name = "field_mask_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:field_mask_proto",
+    config = ":buf.yaml",
+    targets = ["//:field_mask_proto"],
+)
+
+buf_breaking_test(
+    name = "source_context_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:source_context_proto",
+    config = ":buf.yaml",
+    targets = ["//:source_context_proto"],
+)
+
+buf_breaking_test(
+    name = "struct_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:struct_proto",
+    config = ":buf.yaml",
+    targets = ["//:struct_proto"],
+)
+
+buf_breaking_test(
+    name = "timestamp_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:timestamp_proto",
+    config = ":buf.yaml",
+    targets = ["//:timestamp_proto"],
+)
+
+buf_breaking_test(
+    name = "type_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:type_proto",
+    config = ":buf.yaml",
+    targets = ["//:type_proto"],
+)
+
+buf_breaking_test(
+    name = "wrappers_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:wrappers_proto",
+    config = ":buf.yaml",
+    targets = ["//:wrappers_proto"],
+)
+
+buf_breaking_test(
+    name = "compiler_plugin_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:compiler_plugin_proto",
+    config = ":buf.yaml",
+    targets = ["//:compiler_plugin_proto"],
+)
+
+buf_breaking_test(
+    name = "cpp_features_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:cpp_features_proto",
+    config = ":buf.yaml",
+    targets = ["//:cpp_features_proto"],
+)
+
+buf_breaking_test(
+    name = "java_features_proto_breaking",
+    against = "@com_google_protobuf_previous_release//:java_features_proto",
+    config = ":buf.yaml",
+    targets = ["//:java_features_proto"],
+)
+
+test_suite(
+    name = "proto_breaking",
+    tests = [
+        "any_proto_breaking",
+        "api_proto_breaking",
+        "compiler_plugin_proto_breaking",
+        "cpp_features_proto_breaking",
+        "descriptor_proto_breaking",
+        "duration_proto_breaking",
+        "empty_proto_breaking",
+        "field_mask_proto_breaking",
+        "java_features_proto_breaking",
+        "source_context_proto_breaking",
+        "struct_proto_breaking",
+        "timestamp_proto_breaking",
+        "type_proto_breaking",
+        "wrappers_proto_breaking",
+    ],
+)

compatibility/buf.yaml

@@ -0,0 +1 @@
+version: v1

protobuf_version.bzl

@@ -4,3 +4,4 @@ PROTOBUF_JAVA_VERSION = "4.29.0"
 PROTOBUF_PYTHON_VERSION = "5.29.0"
 PROTOBUF_PHP_VERSION = "4.29.0"
 PROTOBUF_RUBY_VERSION = "4.29.0"
+PROTOBUF_PREVIOUS_RELEASE = "28.0-rc1"