Adds Rubocop rule to enforce class_methods over module ClassMethods

3 files changed, 115 insertions, 0 deletions

diff --git a/rubocop/cop/prefer_class_methods_over_module.rb b/rubocop/cop/prefer_class_methods_over_module.rb
new file mode 100644
index 00000000000..bd91c663e58
--- /dev/null
+++ b/rubocop/cop/prefer_class_methods_over_module.rb
@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    # Enforces the use of 'class_methods' instead of 'module ClassMethods'
+    # For more information see: https://gitlab.com/gitlab-org/gitlab-ce/issues/50414
+    #
+    # @example
+    #   # bad
+    #   module Foo
+    #     module ClassMethods
+    #       def a_class_method
+    #       end
+    #     end
+    #   end
+    #
+    #   # good
+    #   module Foo
+    #     class_methods do
+    #       def a_class_method
+    #       end
+    #     end
+    #   end
+    #
+    class PreferClassMethodsOverModule < RuboCop::Cop::Cop
+      include RangeHelp
+
+      MSG = 'Do not use module ClassMethods, use class_methods block instead.'
+
+      def on_module(node)
+        add_offense(node) if node.defined_module_name == 'ClassMethods'
+      end
+
+      def autocorrect(node)
+        lambda do |corrector|
+          corrector.replace(module_range(node), 'class_methods do')
+        end
+      end
+
+      private
+
+      def module_range(node)
+        module_node, _ = *node
+        range_between(node.loc.keyword.begin_pos, module_node.source_range.end_pos)
+      end
+    end
+  end
+end
diff --git a/rubocop/rubocop.rb b/rubocop/rubocop.rb
index eaf421a7235..d823fa4edb1 100644
--- a/rubocop/rubocop.rb
+++ b/rubocop/rubocop.rb
@@ -7,6 +7,7 @@ require_relative 'cop/include_sidekiq_worker'
 require_relative 'cop/avoid_return_from_blocks'
 require_relative 'cop/avoid_break_from_strong_memoize'
 require_relative 'cop/line_break_around_conditional_block'
+require_relative 'cop/prefer_class_methods_over_module'
 require_relative 'cop/migration/add_column'
 require_relative 'cop/migration/add_concurrent_foreign_key'
 require_relative 'cop/migration/add_concurrent_index'
diff --git a/spec/rubocop/cop/prefer_class_methods_over_module_spec.rb b/spec/rubocop/cop/prefer_class_methods_over_module_spec.rb
new file mode 100644
index 00000000000..64b1f1b948d
--- /dev/null
+++ b/spec/rubocop/cop/prefer_class_methods_over_module_spec.rb
@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'rubocop'
+require 'rubocop/rspec/support'
+require_relative '../../../rubocop/cop/prefer_class_methods_over_module'
+
+describe RuboCop::Cop::PreferClassMethodsOverModule do
+  include CopHelper
+
+  subject(:cop) { described_class.new }
+
+  it 'flags violation when using ClassMethods' do
+    expect_offense(<<~RUBY)
+      module Foo
+        module ClassMethods
+        ^^^^^^^^^^^^^^^^^^^ Do not use module ClassMethods, use class_methods block instead.
+          def a_class_method
+          end
+        end
+      end
+    RUBY
+  end
+
+  it "doesn't flag violation when using class_methods" do
+    expect_no_offenses(<<~RUBY)
+      module Foo
+        class_methods do
+          def a_class_method
+          end
+        end
+      end
+    RUBY
+  end
+
+  it "doesn't flag violation when not using either class_methods or ClassMethods" do
+    expect_no_offenses(<<~RUBY)
+      module Foo
+        def a_method
+        end
+      end
+    RUBY
+  end
+
+  it 'autocorrects ClassMethods into class_methods' do
+    source = <<~RUBY
+      module Foo
+        module ClassMethods
+          def a_class_method
+          end
+        end
+      end
+    RUBY
+    autocorrected = autocorrect_source(source)
+
+    expected_source = <<~RUBY
+      module Foo
+        class_methods do
+          def a_class_method
+          end
+        end
+      end
+    RUBY
+    expect(autocorrected).to eql(expected_source)
+  end
+end