1 files changed, 45 insertions, 0 deletions
diff --git a/tooling/danger/model_validations.rb b/tooling/danger/model_validations.rb
new file mode 100644
index 00000000000..410c9dd434e
--- /dev/null
+++ b/tooling/danger/model_validations.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require_relative 'suggestor'
+
+module Tooling
+  module Danger
+    module ModelValidations
+      include ::Tooling::Danger::Suggestor
+
+      MODEL_FILES_PATH = 'app/models'
+      MODEL_CONCERN_FILES_PATH = 'app/models/concerns'
+      EE_PREFIX = 'ee/'
+      MODEL_FILES_REGEX = %r{\A(#{EE_PREFIX})?#{MODEL_FILES_PATH}}
+      MODEL_CONCERN_FILES_REGEX = %r{\A(#{EE_PREFIX})?#{MODEL_CONCERN_FILES_PATH}}
+      VALIDATION_METHODS = %w[validates validate validates_each validates_with validates_associated].freeze
+      VALIDATIONS_REGEX = /^\+\s*(.*\.)?(#{VALIDATION_METHODS.join('|')})[( ]/
+
+      CODE_QUALITY_URL = "https://docs.gitlab.com/ee/development/code_review.html#quality"
+      SUGGEST_MR_COMMENT = <<~SUGGEST_COMMENT.freeze
+        Did you consider new validations can break existing records?
+        Please follow the [code quality guidelines about new model validations](#{CODE_QUALITY_URL}) when adding a new
+        model validation.
+
+        If you're adding the validations to a model with no records you can ignore this warning.
+      SUGGEST_COMMENT
+
+      def add_comment_for_added_validations
+        changed_model_files.each do |filename|
+          add_suggestion(
+            filename: filename,
+            regex: VALIDATIONS_REGEX,
+            comment_text: SUGGEST_MR_COMMENT
+          )
+        end
+      end
+
+      def changed_model_files
+        added_files = helper.added_files
+        modified_files = helper.modified_files
+
+        modified_files.grep(MODEL_FILES_REGEX) + added_files.grep(MODEL_CONCERN_FILES_REGEX)
+      end
+    end
+  end
+end