Add new MigrationClassName cop

Author: j-miyake

changelog/new_add_new_migrationclassname_cop.md

@@ -0,0 +1 @@
+* [#644](https://github.com/rubocop/rubocop-rails/pull/644): Add new `Rails/MigrationClassName` cop. ([@johnny-miyake][])

config/default.yml

@@ -527,6 +527,13 @@ Rails/MatchRoute:
     - config/routes.rb
     - config/routes/**/*.rb
 
+Rails/MigrationClassName:
+  Description: 'The class name of the migration should match its file name.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+  Include:
+    - db/migrate/*.rb
+
 Rails/NegateInclude:
   Description: 'Prefer `collection.exclude?(obj)` over `!collection.include?(obj)`.'
   StyleGuide: 'https://rails.rubystyle.guide#exclude'

lib/rubocop/cop/rails/migration_class_name.rb

@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # This cop makes sure that each migration file defines a migration class
+      # whose name matches the file name.
+      # (e.g. `20220224111111_create_users.rb` should define `CreateUsers` class.)
+      #
+      # @example
+      #   # db/migrate/20220224111111_create_users.rb
+      #
+      #   # bad
+      #   class SellBooks < ActiveRecord::Migration[7.0]
+      #   end
+      #
+      #   # good
+      #   class CreateUsers < ActiveRecord::Migration[7.0]
+      #   end
+      #
+      class MigrationClassName < Base
+        extend AutoCorrector
+
+        MSG = 'Replace with `%<corrected_class_name>s` that matches the file name.'
+
+        def on_class(node)
+          snake_class_name = to_snakecase(node.identifier.source)
+
+          return if snake_class_name == basename_without_timestamp
+
+          corrected_class_name = to_camelcase(basename_without_timestamp)
+          message = format(MSG, corrected_class_name: corrected_class_name)
+
+          add_offense(node.identifier, message: message) do |corrector|
+            corrector.replace(node.identifier, corrected_class_name)
+          end
+        end
+
+        private
+
+        def basename_without_timestamp
+          filepath = processed_source.file_path
+          basename = File.basename(filepath, '.rb')
+          basename.sub(/\A\d+_/, '')
+        end
+
+        def to_camelcase(word)
+          word.split('_').map(&:capitalize).join
+        end
+
+        def to_snakecase(word)
+          word
+            .gsub(/([A-Z\d]+)([A-Z][a-z])/, '\1_\2')
+            .gsub(/([a-z\d])([A-Z])/, '\1_\2')
+            .tr('-', '_')
+            .downcase
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -64,6 +64,7 @@
 require_relative 'rails/link_to_blank'
 require_relative 'rails/mailer_name'
 require_relative 'rails/match_route'
+require_relative 'rails/migration_class_name'
 require_relative 'rails/negate_include'
 require_relative 'rails/not_null_column'
 require_relative 'rails/order_by_id'

spec/rubocop/cop/rails/migration_class_name_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::MigrationClassName, :config do
+  let(:filename) { 'db/migrate/20220101050505_create_users.rb' }
+
+  context 'when the class name matches its file name' do
+    it 'does not register an offense' do
+      expect_no_offenses(<<~RUBY, filename)
+        class CreateUsers < ActiveRecord::Migration[7.0]
+        end
+      RUBY
+    end
+  end
+
+  context 'when the class name does not match its file name' do
+    it 'registers an offense' do
+      expect_offense(<<~RUBY, filename)
+        class SellBooks < ActiveRecord::Migration[7.0]
+              ^^^^^^^^^ Replace with `CreateUsers` that matches the file name.
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        class CreateUsers < ActiveRecord::Migration[7.0]
+        end
+      RUBY
+    end
+  end
+end