feat(pubsub): Add pubsub_rollback_schema sample

pubsub/Gemfile

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+source "https://rubygems.org"
+
+gem "google-cloud-pubsub", "~> 3.0"
+
+group :test do
+  gem "rspec"
+  gem "rspec_junit_formatter"
+end

pubsub/rollback_schema.rb

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# [START pubsub_rollback_schema]
+require "google/cloud/pubsub"
+
+def rollback_schema project_id:, schema_id:, revision_id:
+  # project_id = "your-project-id"
+  # schema_id = "your-schema-id"
+  # revision_id = "your-revision-id"
+
+  pubsub = Google::Cloud::PubSub.new project_id: project_id
+  schema_client = pubsub.schema_service_client
+
+  schema_path = "projects/#{project_id}/schemas/#{schema_id}"
+
+  response = schema_client.rollback_schema name: schema_path, revision_id: revision_id
+
+  puts "Rolled back schema: #{response.name}"
+  puts "New revision ID: #{response.revision_id}"
+end
+# [END pubsub_rollback_schema]

pubsub/spec/rollback_schema_spec.rb

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require "rspec"
+require "google/cloud/pubsub"
+require "securerandom"
+require_relative "../rollback_schema"
+
+RSpec.describe "Rollback Schema" do
+  before :all do
+    @project_id = ENV["GOOGLE_CLOUD_PROJECT"]
+    if @project_id.nil?
+      skip "GOOGLE_CLOUD_PROJECT not defined"
+    end
+
+    @pubsub = Google::Cloud::PubSub.new project_id: @project_id
+    @schema_client = @pubsub.schema_service_client
+    @schema_id = "test-schema-#{SecureRandom.hex(4)}"
+    @schema_path = "projects/#{@project_id}/schemas/#{@schema_id}"
+
+    # Create schema (Revision 1)
+    @definition_1 = "syntax = 'proto3'; message Message { string data = 1; }"
+    schema = {
+      name: @schema_path,
+      type: :PROTOCOL_BUFFER,
+      definition: @definition_1
+    }
+    @initial_schema = @schema_client.create_schema(
+      parent: "projects/#{@project_id}",
+      schema: schema,
+      schema_id: @schema_id
+    )
+    @revision_1_id = @initial_schema.revision_id
+
+    # Commit revision (Revision 2)
+    @definition_2 = "syntax = 'proto3'; message Message { string data = 1; string new_field = 2; }"
+    @second_schema = @schema_client.commit_schema(
+      name: @schema_path,
+      schema: {
+        name: @schema_path,
+        type: :PROTOCOL_BUFFER,
+        definition: @definition_2
+      }
+    )
+    @revision_2_id = @second_schema.revision_id
+  end
+
+  after :all do
+    if @schema_client && @schema_path
+      begin
+        @schema_client.delete_schema name: @schema_path
+      rescue StandardError => e
+        puts "Error cleaning up schema: #{e.message}"
+      end
+    end
+  end
+
+  it "rolls back the schema to a previous revision" do
+    expect {
+      rollback_schema(
+        project_id: @project_id,
+        schema_id: @schema_id,
+        revision_id: @revision_1_id
+      )
+    }.to output(/Rolled back schema:.*#{@schema_id}/).to_stdout
+
+    # Verify the current schema revision is indeed a copy of revision 1
+    current_schema = @schema_client.get_schema name: @schema_path
+    expect(current_schema.definition).to eq(@definition_1)
+    expect(current_schema.revision_id).not_to eq(@revision_1_id)
+    expect(current_schema.revision_id).not_to eq(@revision_2_id)
+  end
+end