Preserve prepend semantics for Ruby

However we still want to make ClassMethods work!

And we'll need to fix codes using the wrong include/prepend
along the way. There were a lot of misuses.

lib/gitlab/patch/prependable.rb

@@ -10,42 +10,29 @@ module Gitlab
         end
       end
 
-      module MetaConcern
-        def extended(base)
-          super
-          base.instance_variable_set(:@_prepend_dependencies, [])
-        end
-      end
-
-      def self.prepended(base)
-        super
-        base.singleton_class.prepend MetaConcern
-      end
-
-      def append_features(base)
-        super
-
-        prepend_features(base)
-      end
-
       def prepend_features(base)
-        if base.instance_variable_defined?(:@_prepend_dependencies)
-          base.instance_variable_get(:@_prepend_dependencies) << self
-          false
-        else
         return false if prepended?(base)
 
-          @_prepend_dependencies.each { |dep| base.prepend(dep) }
-
         super
 
         if const_defined?(:ClassMethods)
-            base.singleton_class.prepend const_get(:ClassMethods)
+          klass_methods = const_get(:ClassMethods)
+          base.singleton_class.prepend klass_methods
+          base.instance_variable_set(:@_prepended_class_methods, klass_methods)
         end
 
         if instance_variable_defined?(:@_prepended_block)
           base.class_eval(&@_prepended_block)
         end
+
+        true
+      end
+
+      def class_methods
+        super
+
+        if instance_variable_defined?(:@_prepended_class_methods)
+          const_get(:ClassMethods).prepend @_prepended_class_methods
         end
       end
 
@@ -63,7 +50,6 @@ module Gitlab
       def prepended?(base)
         index = base.ancestors.index(base)
 
-        @_prepend_dependencies.index(self) ||
         base.ancestors[0...index].index(self)
       end
     end

spec/lib/gitlab/patch/prependable_spec.rb

@@ -71,22 +71,41 @@ describe Gitlab::Patch::Prependable do
 
       subject
 
-      expect(prepended_modules).to eq([[subject, ee], [subject, ce]])
+      expect(prepended_modules).to eq([[ce, ee]])
+    end
+
+    context 'overriding a method' do
+      before do
+        subject.module_eval do
+          def self.class_name
+            'Custom'
+          end
+
+          def name
+            'custom'
+          end
+        end
+      end
+
+      it 'returns values from the class' do
+        expect(subject.new.name).to eq('custom')
+        expect(subject.class_name).to eq('Custom')
+      end
     end
   end
 
   describe 'a class prepending a concern prepending a concern' do
     subject { Class.new.prepend(ce) }
 
-    it 'returns values from prepended module ce' do
-      expect(subject.new.name).to eq('ce')
-      expect(subject.class_name).to eq('CE')
+    it 'returns values from prepended module ee' do
+      expect(subject.new.name).to eq('ee')
+      expect(subject.class_name).to eq('EE')
     end
 
     it 'prepends only once' do
       subject.prepend(ce)
 
-      expect(prepended_modules).to eq([[subject, ee], [subject, ce]])
+      expect(prepended_modules).to eq([[ce, ee], [subject, ce]])
     end
   end