From 8af40870e2208612a5af34e19f231032745a7f90 Mon Sep 17 00:00:00 2001
From: Jacopo <beschi.jacopo@gmail.com>
Date: Mon, 27 Aug 2018 14:23:25 +0200
Subject: [PATCH] Applies rule only when extending ActiveSupport::Concern

---
 .../cop/prefer_class_methods_over_module.rb   | 24 +++++++++++++++++--
 .../prefer_class_methods_over_module_spec.rb  | 23 +++++++++++++++++-
 2 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/rubocop/cop/prefer_class_methods_over_module.rb b/rubocop/cop/prefer_class_methods_over_module.rb
index bd91c663e58..496d2ed249f 100644
--- a/rubocop/cop/prefer_class_methods_over_module.rb
+++ b/rubocop/cop/prefer_class_methods_over_module.rb
@@ -2,12 +2,14 @@
 
 module RuboCop
   module Cop
-    # Enforces the use of 'class_methods' instead of 'module ClassMethods'
+    # Enforces the use of 'class_methods' instead of 'module ClassMethods' for activesupport concerns.
     # For more information see: https://gitlab.com/gitlab-org/gitlab-ce/issues/50414
     #
     # @example
     #   # bad
     #   module Foo
+    #     extend ActiveSupport::Concern
+    #
     #     module ClassMethods
     #       def a_class_method
     #       end
@@ -16,6 +18,8 @@ module RuboCop
     #
     #   # good
     #   module Foo
+    #     extend ActiveSupport::Concern
+    #
     #     class_methods do
     #       def a_class_method
     #       end
@@ -27,8 +31,12 @@ module RuboCop
 
       MSG = 'Do not use module ClassMethods, use class_methods block instead.'
 
+      def_node_matcher :extend_activesupport_concern?, <<~PATTERN
+        (:send nil? :extend (:const (:const nil? :ActiveSupport) :Concern))
+      PATTERN
+
       def on_module(node)
-        add_offense(node) if node.defined_module_name == 'ClassMethods'
+        add_offense(node) if node.defined_module_name == 'ClassMethods' && extends_activesupport_concern?(node)
       end
 
       def autocorrect(node)
@@ -39,6 +47,18 @@ module RuboCop
 
       private
 
+      def extends_activesupport_concern?(node)
+        container_module(node.parent)&.descendants.any? do |descendant|
+          extend_activesupport_concern?(descendant)
+        end
+      end
+
+      def container_module(node)
+        node = node.parent until node.type == :module
+
+        node
+      end
+
       def module_range(node)
         module_node, _ = *node
         range_between(node.loc.keyword.begin_pos, module_node.source_range.end_pos)
diff --git a/spec/rubocop/cop/prefer_class_methods_over_module_spec.rb b/spec/rubocop/cop/prefer_class_methods_over_module_spec.rb
index 64b1f1b948d..527c236eecf 100644
--- a/spec/rubocop/cop/prefer_class_methods_over_module_spec.rb
+++ b/spec/rubocop/cop/prefer_class_methods_over_module_spec.rb
@@ -10,9 +10,11 @@ describe RuboCop::Cop::PreferClassMethodsOverModule do
 
   subject(:cop) { described_class.new }
 
-  it 'flags violation when using ClassMethods' do
+  it 'flags violation when using module ClassMethods' do
     expect_offense(<<~RUBY)
       module Foo
+        extend ActiveSupport::Concern
+
         module ClassMethods
         ^^^^^^^^^^^^^^^^^^^ Do not use module ClassMethods, use class_methods block instead.
           def a_class_method
@@ -25,6 +27,8 @@ describe RuboCop::Cop::PreferClassMethodsOverModule do
   it "doesn't flag violation when using class_methods" do
     expect_no_offenses(<<~RUBY)
       module Foo
+        extend ActiveSupport::Concern
+
         class_methods do
           def a_class_method
           end
@@ -33,9 +37,22 @@ describe RuboCop::Cop::PreferClassMethodsOverModule do
     RUBY
   end
 
+  it "doesn't flag violation when module is not extending ActiveSupport::Concern" do
+    expect_no_offenses(<<~RUBY)
+      module Foo
+        module ClassMethods
+          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
+        extend ActiveSupport::Concern
+
         def a_method
         end
       end
@@ -45,6 +62,8 @@ describe RuboCop::Cop::PreferClassMethodsOverModule do
   it 'autocorrects ClassMethods into class_methods' do
     source = <<~RUBY
       module Foo
+        extend ActiveSupport::Concern
+
         module ClassMethods
           def a_class_method
           end
@@ -55,6 +74,8 @@ describe RuboCop::Cop::PreferClassMethodsOverModule do
 
     expected_source = <<~RUBY
       module Foo
+        extend ActiveSupport::Concern
+
         class_methods do
           def a_class_method
           end