Add gitaly gem bump danger check

danger/gitaly/Dangerfile

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+TEMPLATE_MESSAGE = <<~MSG
+This merge request requires coordination with gitaly deployments.
+Before merging this merge request we should verify that gitaly
+running in production already implements the new gRPC interface
+included here.
+
+Failing to do so will introduce a [non backward compatible
+change](https://docs.gitlab.com/ee/development/multi_version_compatibility.html)
+during canary depoyment that can cause an incident.
+
+1. Identify the gitaly MR introducing the new interface
+1. Verify that the environment widget contains a `gprd` deployment
+MSG
+
+changed_lines = helper.changed_lines('Gemfile.lock')
+if changed_lines.any? { |line| line =~ /^\+\s+gitaly \(/ }
+  warn 'Changing gitaly gem can cause a multi-version incompatibility incident'
+
+  markdown(TEMPLATE_MESSAGE)
+end

spec/tooling/danger/project_helper_spec.rb

@@ -221,7 +221,7 @@
 
   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: changelog, database, datateam, documentation, duplicate_yarn_dependencies, eslint, karma, pajamas, pipeline, prettier, product_intelligence, utility_css')
+      expect(described_class.local_warning_message).to eq('==> Only the following Danger rules can be run locally: changelog, database, datateam, documentation, duplicate_yarn_dependencies, eslint, gitaly, karma, pajamas, pipeline, prettier, product_intelligence, utility_css')
     end
   end
 

tooling/danger/project_helper.rb

@@ -10,6 +10,7 @@ module ProjectHelper
         documentation
         duplicate_yarn_dependencies
         eslint
+        gitaly
         karma
         pajamas
         pipeline