diff --git a/danger/ignored_model_columns/Dangerfile b/danger/ignored_model_columns/Dangerfile
new file mode 100644
index 0000000000000000000000000000000000000000..e11566f90f2a6a4d19c90798b09b826d566c7547
--- /dev/null
+++ b/danger/ignored_model_columns/Dangerfile
@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+ignored_model_columns.add_comment_for_ignored_model_columns
diff --git a/danger/plugins/ignored_model_columns.rb b/danger/plugins/ignored_model_columns.rb
new file mode 100644
index 0000000000000000000000000000000000000000..8e0024a94d642515dc061d53d5b01e7a052f4a8d
--- /dev/null
+++ b/danger/plugins/ignored_model_columns.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+require_relative '../../tooling/danger/ignored_model_columns'
+
+module Danger
+ class IgnoredModelColumns < ::Danger::Plugin
+ include Tooling::Danger::IgnoredModelColumns
+ end
+end
diff --git a/spec/tooling/danger/ignored_model_columns_spec.rb b/spec/tooling/danger/ignored_model_columns_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..737b6cce0778c9f76a0b9c864584e065d9c87005
--- /dev/null
+++ b/spec/tooling/danger/ignored_model_columns_spec.rb
@@ -0,0 +1,145 @@
+# frozen_string_literal: true
+
+require 'danger'
+require 'gitlab/dangerfiles/spec_helper'
+
+require_relative '../../../tooling/danger/ignored_model_columns'
+require_relative '../../../tooling/danger/project_helper'
+
+RSpec.describe Tooling::Danger::IgnoredModelColumns, feature_category: :tooling do
+ subject(:ignored_model_columns) { fake_danger.new(helper: fake_helper) }
+
+ let(:fake_danger) { DangerSpecHelper.fake_danger.include(described_class) }
+ let(:fake_project_helper) { instance_double(Tooling::Danger::ProjectHelper) }
+ let(:comment) { described_class::COMMENT.chomp }
+ let(:file_diff) do
+ File.read(File.expand_path("../fixtures/#{fixture}", __dir__)).split("\n")
+ end
+
+ include_context "with dangerfile"
+
+ describe '#add_comment_for_ignored_model_columns' do
+ let(:file_lines) { file_diff.map { |line| line.delete_prefix('+').delete_prefix('-') } }
+
+ before do
+ allow(ignored_model_columns).to receive(:project_helper).and_return(fake_project_helper)
+ allow(ignored_model_columns.project_helper).to receive(:file_lines).and_return(file_lines)
+ allow(ignored_model_columns.helper).to receive(:all_changed_files).and_return([filename])
+ allow(ignored_model_columns.helper).to receive(:changed_lines).with(filename).and_return(file_diff)
+ end
+
+ context 'when table column is renamed in a regular migration' do
+ let(:filename) { 'db/migrate/rename_my_column_migration.rb' }
+ let(:fixture) { 'rename_column_migration.txt' }
+ let(:matching_lines) { [7, 11, 15, 19, 23, 27, 31, 35, 39] }
+
+ it 'adds comment at the correct line' do
+ matching_lines.each do |line_number|
+ expect(ignored_model_columns).to receive(:markdown).with("\n#{comment}", file: filename, line: line_number)
+ end
+
+ ignored_model_columns.add_comment_for_ignored_model_columns
+ end
+ end
+
+ context 'when table column is renamed in a post migration' do
+ let(:filename) { 'db/post_migrate/remove_column_migration.rb' }
+ let(:fixture) { 'remove_column_migration.txt' }
+ let(:matching_lines) { [7, 8, 16, 24, 32, 40, 48, 56, 64, 72] }
+
+ it 'adds comment at the correct line' do
+ matching_lines.each do |line_number|
+ expect(ignored_model_columns).to receive(:markdown).with("\n#{comment}", file: filename, line: line_number)
+ end
+
+ ignored_model_columns.add_comment_for_ignored_model_columns
+ end
+ end
+
+ context 'when table cleanup is performed in a post migration' do
+ let(:filename) { 'db/post_migrate/cleanup_conversion_big_int_migration.rb' }
+ let(:fixture) { 'cleanup_conversion_migration.txt' }
+ let(:matching_lines) { [7, 11, 15, 19, 23, 27, 31, 35, 39] }
+
+ it 'adds comment at the correct line' do
+ matching_lines.each do |line_number|
+ expect(ignored_model_columns).to receive(:markdown).with("\n#{comment}", file: filename, line: line_number)
+ end
+
+ ignored_model_columns.add_comment_for_ignored_model_columns
+ end
+ end
+
+ context 'when a regular migration does not rename table column' do
+ let(:filename) { 'db/migrate/my_migration.rb' }
+ let(:file_diff) do
+ [
+ "+ undo_cleanup_concurrent_column_rename(:my_table, :old_column, :new_column)",
+ "- cleanup_concurrent_column_rename(:my_table, :new_column, :old_column)"
+ ]
+ end
+
+ let(:file_lines) do
+ [
+ ' def up',
+ ' undo_cleanup_concurrent_column_rename(:my_table, :old_column, :new_column)',
+ ' end'
+ ]
+ end
+
+ it 'does not add comment' do
+ expect(ignored_model_columns).not_to receive(:markdown)
+
+ ignored_model_columns.add_comment_for_ignored_model_columns
+ end
+ end
+
+ context 'when a post migration does not remove table column' do
+ let(:filename) { 'db/migrate/my_migration.rb' }
+ let(:file_diff) do
+ [
+ "+ add_column(:my_table, :my_column, :type)",
+ "- remove_column(:my_table, :my_column)"
+ ]
+ end
+
+ let(:file_lines) do
+ [
+ ' def up',
+ ' add_column(:my_table, :my_column, :type)',
+ ' end'
+ ]
+ end
+
+ it 'does not add comment' do
+ expect(ignored_model_columns).not_to receive(:markdown)
+
+ ignored_model_columns.add_comment_for_ignored_model_columns
+ end
+ end
+
+ context 'when a post migration does not convert table column' do
+ let(:filename) { 'db/migrate/my_migration.rb' }
+ let(:file_diff) do
+ [
+ "+ restore_conversion_of_integer_to_bigint(TABLE, COLUMNS)",
+ "- cleanup_conversion_of_integer_to_bigint(TABLE, COLUMNS)"
+ ]
+ end
+
+ let(:file_lines) do
+ [
+ ' def up',
+ ' cleanup_conversion_of_integer_to_bigint(TABLE, COLUMNS)',
+ ' end'
+ ]
+ end
+
+ it 'does not add comment' do
+ expect(ignored_model_columns).not_to receive(:markdown)
+
+ ignored_model_columns.add_comment_for_ignored_model_columns
+ end
+ end
+ end
+end
diff --git a/spec/tooling/fixtures/cleanup_conversion_migration.txt b/spec/tooling/fixtures/cleanup_conversion_migration.txt
new file mode 100644
index 0000000000000000000000000000000000000000..14a7937b4695b8913989da3305b669591c899985
--- /dev/null
+++ b/spec/tooling/fixtures/cleanup_conversion_migration.txt
@@ -0,0 +1,44 @@
++# frozen_string_literal: true
++
++class TestMigration < Gitlab::Database::Migration[2.1]
++ disable_ddl_transaction!
++
++ def up
++ cleanup_conversion_of_integer_to_bigint :my_table, :my_column
++ end
++
++ def up
++ cleanup_conversion_of_integer_to_bigint 'my_table', 'my_column'
++ end
++
++ def up
++ cleanup_conversion_of_integer_to_bigint "my_table", "my_column", "new_column"
++ end
++
++ def up
++ cleanup_conversion_of_integer_to_bigint TABLE_NAME, MY_COLUMN
++ end
++
++ def up
++ cleanup_conversion_of_integer_to_bigint(:my_table, :my_column)
++ end
++
++ def up
++ cleanup_conversion_of_integer_to_bigint('my_table', 'my_column')
++ end
++
++ def up
++ cleanup_conversion_of_integer_to_bigint("my_table", "my_column")
++ end
++
++ def up
++ cleanup_conversion_of_integer_to_bigint(TABLE_NAME, MY_COLUMN)
++ end
++
++ def up
++ cleanup_conversion_of_integer_to_bigint(
++ :my_table,
++ :my_column
++ )
++ end
++end
diff --git a/spec/tooling/fixtures/remove_column_migration.txt b/spec/tooling/fixtures/remove_column_migration.txt
new file mode 100644
index 0000000000000000000000000000000000000000..885f0060d920fa628d8729dea313cf63d5c1ae4d
--- /dev/null
+++ b/spec/tooling/fixtures/remove_column_migration.txt
@@ -0,0 +1,84 @@
++# frozen_string_literal: true
++
++class TestMigration < Gitlab::Database::Migration[2.1]
++ disable_ddl_transaction!
++
++ def up
++ remove_column :my_table, :my_column
++ remove_column :my_other_table, :my_column
++ end
++
++ def down
++ remove_column :my_table, :my_column
++ end
++
++ def up
++ remove_column 'my_table', 'my_column'
++ end
++
++ def down
++ remove_column 'my_table', 'my_column'
++ end
++
++ def up
++ remove_column "my_table", "my_column", "new_column"
++ end
++
++ def down
++ remove_column "my_table", "my_column", "new_column"
++ end
++
++ def up
++ remove_column TABLE_NAME, MY_COLUMN
++ end
++
++ def down
++ remove_column TABLE_NAME, MY_COLUMN
++ end
++
++ def up
++ remove_column(:my_table, :my_column)
++ end
++
++ def down
++ remove_column(:my_table, :my_column)
++ end
++
++ def up
++ remove_column('my_table', 'my_column')
++ end
++
++ def down
++ remove_column('my_table', 'my_column')
++ end
++
++ def up
++ remove_column("my_table", "my_column")
++ end
++
++ def down
++ remove_column("my_table", "my_column")
++ end
++
++ def up
++ remove_column(TABLE_NAME, MY_COLUMN)
++ end
++
++ def down
++ remove_column(TABLE_NAME, MY_COLUMN)
++ end
++
++ def up
++ remove_column(
++ :my_table,
++ :my_column
++ )
++ end
++
++ def down
++ remove_column(
++ :my_table,
++ :my_column
++ )
++ end
++end
diff --git a/spec/tooling/fixtures/rename_column_migration.txt b/spec/tooling/fixtures/rename_column_migration.txt
new file mode 100644
index 0000000000000000000000000000000000000000..e79029219a53c65af42aaffc44563d853cdbc060
--- /dev/null
+++ b/spec/tooling/fixtures/rename_column_migration.txt
@@ -0,0 +1,45 @@
++# frozen_string_literal: true
++
++class TestMigration < Gitlab::Database::Migration[2.1]
++ disable_ddl_transaction!
++
++ def up
++ cleanup_concurrent_column_rename :my_table, :old_column, :new_column
++ end
++
++ def up
++ cleanup_concurrent_column_rename 'my_table', 'old_column', 'new_column'
++ end
++
++ def up
++ cleanup_concurrent_column_rename "my_table", "old_column", "new_column"
++ end
++
++ def up
++ cleanup_concurrent_column_rename TABLE_NAME, OLD_COLUMN_NAME, NEW_COLUMN_NAME
++ end
++
++ def up
++ cleanup_concurrent_column_rename(:my_table, :old_column, :new_column)
++ end
++
++ def up
++ cleanup_concurrent_column_rename('my_table', 'old_column', 'new_column')
++ end
++
++ def up
++ cleanup_concurrent_column_rename("my_table", "old_column", "new_column")
++ end
++
++ def up
++ cleanup_concurrent_column_rename(TABLE_NAME, OLD_COLUMN_NAME, NEW_COLUMN_NAME)
++ end
++
++ def up
++ cleanup_concurrent_column_rename(
++ :my_table,
++ :old_column,
++ :new_column
++ )
++ end
++end
diff --git a/tooling/danger/ignored_model_columns.rb b/tooling/danger/ignored_model_columns.rb
new file mode 100644
index 0000000000000000000000000000000000000000..50379eed85ccf2842e728c009ce05e3787614ced
--- /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