Add `error_code` to cherry-pick/revert responses

lib/api/commits.rb

@@ -223,7 +223,7 @@ module API
           present user_project.repository.commit(result[:result]),
             with: Entities::Commit
         else
-          render_api_error!(result[:message], 400)
+          error!(result.slice(:message, :error_code), 400, header)
         end
       end
 
@@ -257,7 +257,7 @@ module API
           present user_project.repository.commit(result[:result]),
             with: Entities::Commit
         else
-          render_api_error!(result[:message], 400)
+          error!(result.slice(:message, :error_code), 400, header)
         end
       end
 

spec/requests/api/commits_spec.rb

@@ -1376,6 +1376,12 @@ describe API::Commits do
         it_behaves_like '400 response' do
           let(:request) { post api(route, current_user), params: { branch: 'markdown' } }
         end
+
+        it 'includes an error_code in the response' do
+          post api(route, current_user), params: { branch: 'markdown' }
+
+          expect(json_response['error_code']).to eq 'empty'
+        end
       end
 
       context 'when ref contains a dot' do
@@ -1535,6 +1541,19 @@ describe API::Commits do
           let(:request) { post api(route, current_user) }
         end
       end
+
+      context 'when commit is already reverted in the target branch' do
+        it 'includes an error_code in the response' do
+          # First one actually reverts
+          post api(route, current_user), params: { branch: 'markdown' }
+
+          # Second one is redundant and should be empty
+          post api(route, current_user), params: { branch: 'markdown' }
+
+          expect(response).to have_gitlab_http_status(400)
+          expect(json_response['error_code']).to eq 'empty'
+        end
+      end
     end
 
     context 'when authenticated', 'as a developer' do