Allow GitlabPostReceive to print warnings

Warnings are printed using the same method that prints broadcast
messages. This ensures that whatever warnings are returned will be
displayed correctly.

lib/gitlab_post_receive.rb

@@ -28,6 +28,7 @@ class GitlabPostReceive
     print_merge_request_links(response['merge_request_urls']) if response['merge_request_urls']
     puts response['redirected_message'] if response['redirected_message']
     puts response['project_created_message'] if response['project_created_message']
+    print_warnings(response['warnings']) if response['warnings']
 
     response['reference_counter_decreased']
   rescue GitlabNet::ApiUnreachableError
@@ -59,6 +60,11 @@ class GitlabPostReceive
     puts
   end
 
+  def print_warnings(warnings)
+    message = "WARNINGS:\n#{warnings}"
+    print_broadcast_message(message)
+  end
+
   def print_broadcast_message(message)
     # A standard terminal window is (at least) 80 characters wide.
     total_width = 80

spec/gitlab_post_receive_spec.rb

@@ -96,7 +96,21 @@ describe GitlabPostReceive do
           expect(gitlab_post_receive.exec).to eq(true)
         end
       end
+    end
+
+    context 'when warnings available' do
+      let(:response) do
+        {
+          'reference_counter_decreased' => true,
+          'warnings' => 'My warning message'
+        }
+      end
 
+      it 'prints warnings the same ways as broadcast messages' do
+        expect_any_instance_of(GitlabNet).to receive(:post_receive).and_return(response)
+        expect(gitlab_post_receive).to receive(:print_broadcast_message).with("WARNINGS:\nMy warning message")
+        expect(gitlab_post_receive.exec).to eq(true)
+      end
     end
 
     context 'when redirected message available' do