Add Danger to validate pipeline changes

Use Danger to provide guidance to consider
effects of pipeline changes and the need
to communicate broadly

danger/pipeline/Dangerfile

+# frozen_string_literal: true
+
+MESSAGE = <<~MESSAGE
+## Pipeline Changes
+
+This Merge Request contains changes to the pipeline configuration for the GitLab project.
+
+Please consider the effect of the changes in this Merge Request on the following:
+- Effects on different [pipeline types](https://docs.gitlab.com/ee/development/pipelines.html#pipelines-for-merge-requests)
+- Effects on non-canonical projects (`gitlab-foss`, `security`, etc)
+- Effects on [pipeline performance](https://about.gitlab.com/handbook/engineering/quality/performance-indicators/#average-merge-request-pipeline-duration-for-gitlab)
+- Effects on fork pipelines
+
+Please consider communicating these changes to the broader team following the [communication guideline for pipeline changes](https://about.gitlab.com/handbook/engineering/quality/engineering-productivity-team/#pipeline-changes)
+MESSAGE
+
+if helper.has_ci_changes?
+  markdown(MESSAGE)
+end

lib/gitlab/danger/helper.rb

@@ -268,6 +268,10 @@ module Gitlab
       def has_database_scoped_labels?(current_mr_labels)
         current_mr_labels.any? { |label| label.start_with?('database::') }
       end
+
+      def has_ci_changes?
+        changed_files(%r{\A(\.gitlab-ci\.yml|\.gitlab/ci/)}).any?
+      end
     end
   end
 end

lib/gitlab_danger.rb

@@ -14,6 +14,7 @@ class GitlabDanger
     product_analytics
     utility_css
     pajamas
+    pipeline
   ].freeze
 
   CI_ONLY_RULES ||= %w[

spec/lib/gitlab/danger/helper_spec.rb

@@ -591,4 +591,30 @@ RSpec.describe Gitlab::Danger::Helper do
       expect(helper.prepare_labels_for_mr([])).to eq('')
     end
   end
+
+  describe '#has_ci_changes?' do
+    context 'when .gitlab/ci is changed' do
+      it 'returns true' do
+        expect(helper).to receive(:all_changed_files).and_return(%w[migration.rb .gitlab/ci/test.yml])
+
+        expect(helper.has_ci_changes?).to be_truthy
+      end
+    end
+
+    context 'when .gitlab-ci.yml is changed' do
+      it 'returns true' do
+        expect(helper).to receive(:all_changed_files).and_return(%w[migration.rb .gitlab-ci.yml])
+
+        expect(helper.has_ci_changes?).to be_truthy
+      end
+    end
+
+    context 'when neither .gitlab/ci/ or .gitlab-ci.yml is changed' do
+      it 'returns false' do
+        expect(helper).to receive(:all_changed_files).and_return(%w[migration.rb nested/.gitlab-ci.yml])
+
+        expect(helper.has_ci_changes?).to be_falsey
+      end
+    end
+  end
 end

spec/lib/gitlab_danger_spec.rb

 # frozen_string_literal: true
 
-require 'spec_helper'
+require 'fast_spec_helper'
 
 RSpec.describe GitlabDanger do
   let(:gitlab_danger_helper) { nil }
@@ -9,7 +9,7 @@ RSpec.describe GitlabDanger do
 
   describe '.local_warning_message' do
     it 'returns an informational message with rules that can run' do
-      expect(described_class.local_warning_message).to eq('==> Only the following Danger rules can be run locally: changes_size, documentation, frozen_string, duplicate_yarn_dependencies, prettier, eslint, karma, database, commit_messages, product_analytics, utility_css, pajamas')
+      expect(described_class.local_warning_message).to eq("==> Only the following Danger rules can be run locally: #{described_class::LOCAL_RULES.join(', ')}")
     end
   end