1 files changed, 76 insertions, 0 deletions
diff --git a/tooling/danger/ignored_model_columns.rb b/tooling/danger/ignored_model_columns.rb
new file mode 100644
index 00000000000..50379eed85c
--- /dev/null
+++ b/tooling/danger/ignored_model_columns.rb
@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+require_relative 'suggestor'
+
+module Tooling
+  module Danger
+    module IgnoredModelColumns
+      include ::Tooling::Danger::Suggestor
+
+      METHODS = %w[remove_column cleanup_concurrent_column_rename cleanup_conversion_of_integer_to_bigint].freeze
+      MIGRATION_FILES_REGEX = %r{^db/(post_)?migrate}
+      MIGRATION_METHODS_REGEX = /^\+\s*(.*\.)?(#{METHODS.join('|')})[(\s]/
+      UP_METHOD_REGEX = /^.+(def\sup)/
+      END_METHOD_REGEX = /^.+(end)/
+      DOC_URL = "https://docs.gitlab.com/ee/development/database/avoiding_downtime_in_migrations.html"
+
+      COMMENT = <<~COMMENT.freeze
+        Column operations, like [dropping](#{DOC_URL}#dropping-columns), [renaming](#{DOC_URL}#renaming-columns) or
+        [primary key conversion](#{DOC_URL}#migrating-integer-primary-keys-to-bigint), require columns to be ignored in
+        the model. This step is necessary because Rails caches the columns and re-uses it in various places across the
+        application. Please ensure that columns are properly ignored in the model.
+      COMMENT
+
+      def add_comment_for_ignored_model_columns
+        migration_files.each do |filename|
+          add_suggestion(filename: filename, regex: MIGRATION_METHODS_REGEX, comment_text: COMMENT)
+        end
+      end
+
+      private
+
+      # This method was overwritten to make use of +up_method_lines+.
+      # It's necessary to only match lines that are inside the +up+ block in a migration file.
+      #
+      # @return [Integer, Nil] the line number - only if the line is from within a +up+ method
+      def find_line_number(file_lines, searched_line, exclude_indexes: [])
+        lines_to_search = up_method_lines(file_lines)
+
+        _, index = file_lines.each_with_index.find do |file_line, index|
+          next unless lines_to_search.include?(index)
+
+          file_line == searched_line && !exclude_indexes.include?(index) # rubocop:disable Rails/NegateInclude
+        end
+
+        index
+      end
+
+      # Return the line numbers from within the up method
+      #
+      # @example
+      #         line 0 def up
+      #         line 1   cleanup_conversion_of_integer_to_bigint():my_table, :my_column)
+      #         line 2   remove_column(:my_table, :my_column)
+      #         line 3   other_method
+      #         line 4 end
+      #
+      #         => [1, 2, 3]
+      def up_method_lines(file_lines)
+        capture_up_block = false
+        up_method_content_lines = []
+
+        file_lines.each_with_index do |content, line_number|
+          capture_up_block = false if capture_up_block && END_METHOD_REGEX.match?(content)
+          up_method_content_lines << line_number if capture_up_block
+          capture_up_block = true if UP_METHOD_REGEX.match?(content)
+        end
+
+        up_method_content_lines
+      end
+
+      def migration_files
+        helper.all_changed_files.grep(MIGRATION_FILES_REGEX)
+      end
+    end
+  end
+end