Add danger check for required migration stop

Add a check to notify developers for possible
implication of finalizing heavy data migration

danger/plugins/required_stops.rb

+# frozen_string_literal: true
+
+require_relative '../../tooling/danger/required_stops'
+
+module Danger
+  class RequiredStops < ::Danger::Plugin
+    # Put the helper code somewhere it can be tested
+    include Tooling::Danger::RequiredStops
+  end
+end

danger/required_stops/Dangerfile

+# frozen_string_literal: true
+
+required_stops.add_comment_for_finalized_migrations

spec/tooling/danger/required_stops_spec.rb

+# frozen_string_literal: true
+
+require 'gitlab-dangerfiles'
+require 'danger'
+require 'danger/plugins/internal/helper'
+require 'gitlab/dangerfiles/spec_helper'
+
+require_relative '../../../tooling/danger/required_stops'
+require_relative '../../../tooling/danger/project_helper'
+
+RSpec.describe Tooling::Danger::RequiredStops, feature_category: :tooling do
+  include_context "with dangerfile"
+
+  let(:fake_danger) { DangerSpecHelper.fake_danger.include(described_class) }
+  let(:fake_project_helper) { instance_double(Tooling::Danger::ProjectHelper) }
+  let(:warning_comment) { described_class::WARNING_COMMENT.chomp }
+
+  subject(:required_stops) { fake_danger.new(helper: fake_helper) }
+
+  before do
+    allow(required_stops).to receive(:project_helper).and_return(fake_project_helper)
+  end
+
+  describe '#add_comment_for_finalized_migrations' do
+    let(:file_lines) { file_diff.map { |line| line.delete_prefix('+').delete_prefix('-') } }
+
+    before do
+      allow(required_stops.project_helper).to receive(:file_lines).and_return(file_lines)
+      allow(required_stops.helper).to receive(:all_changed_files).and_return([filename])
+      allow(required_stops.helper).to receive(:changed_lines).with(filename).and_return(file_diff)
+    end
+
+    shared_examples "adds comment to added migration finalizations" do
+      context 'when model has a newly added migration finalization' do
+        let(:file_diff) do
+          [
+            "+ def up",
+            "+ finalize_background_migration(MIGRATION)",
+            "+ end",
+            "+ def up",
+            "+ finalize_background_migration('MyMigration')",
+            "+ end",
+            "+ def up",
+            "+ ensure_batched_background_migration_is_finished(",
+            "+ end",
+            "+ def up",
+            "+ ensure_batched_background_migration_is_finished('MyMigration')",
+            "+ end",
+            "+ def up",
+            "+ finalize_batched_background_migration(",
+            "+ end",
+            "+ def up",
+            "+ finalize_batched_background_migration('MyMigration')",
+            "+ end"
+          ]
+        end
+
+        it 'adds comment at the correct line' do
+          matching_line_numbers = [2, 5, 8, 11, 14, 17]
+          matching_line_numbers.each do |line_number|
+            expect(required_stops).to receive(:markdown).with("\n#{warning_comment}", file: filename, line: line_number)
+          end
+
+          required_stops.add_comment_for_finalized_migrations
+        end
+      end
+
+      context 'when model does not have migration finalization statement' do
+        let(:file_diff) do
+          [
+            "+ queue_batched_background_migration(",
+            "- ensure_batched_background_migration_is_finished("
+          ]
+        end
+
+        it 'does not add comment' do
+          expect(required_stops).not_to receive(:markdown)
+
+          required_stops.add_comment_for_finalized_migrations
+        end
+      end
+    end
+
+    context 'when model has a newly added migration finalization' do
+      context 'with regular migration' do
+        let(:filename) { 'db/migrate/my_migration.rb' }
+
+        include_examples 'adds comment to added migration finalizations'
+      end
+
+      context 'with post migration' do
+        let(:filename) { 'db/post_migrate/my_migration.rb' }
+
+        include_examples 'adds comment to added migration finalizations'
+      end
+    end
+  end
+end

tooling/danger/required_stops.rb

+# frozen_string_literal: true
+
+require_relative 'suggestor'
+
+module Tooling
+  module Danger
+    module RequiredStops
+      include ::Tooling::Danger::Suggestor
+
+      MIGRATION_FILES_REGEX = %r{^db/(post_)?migrate}
+
+      MIGRATION_FINALIZE_METHODS = %w[finalize_background_migration ensure_batched_background_migration_is_finished
+        finalize_batched_background_migration].freeze
+      MIGRATION_FINALIZE_REGEX = /^\+\s*(.*\.)?(#{MIGRATION_FINALIZE_METHODS.join('|')})[( ]/
+
+      DOC_URL = "https://docs.gitlab.com/ee/development/database/required_stops.html"
+      WARNING_COMMENT = <<~COMMENT.freeze
+        Finalizing data migration might be time consuming and require a [required stop](#{DOC_URL}).
+        Check the timings of the underlying data migration.
+        If possible postpone the finalization to the scheduled required stop.
+        If postponing is impossible please create new required stop as documentation suggests.
+      COMMENT
+
+      def add_comment_for_finalized_migrations
+        migration_files.each do |filename|
+          add_suggestion(
+            filename: filename,
+            regex: MIGRATION_FINALIZE_REGEX,
+            comment_text: WARNING_COMMENT
+          )
+        end
+      end
+
+      private
+
+      def migration_files
+        helper.all_changed_files.grep(MIGRATION_FILES_REGEX)
+      end
+    end
+  end
+end