Show hook errors for FF merges

app/services/merge_requests/ff_merge_service.rb

@@ -13,6 +13,10 @@ module MergeRequests
                           source,
                           merge_request.target_branch,
                           merge_request: merge_request)
+    rescue GitHooksService::PreReceiveError => e
+      raise MergeError, e.message
+    rescue StandardError => e
+      raise MergeError, "Something went wrong during merge: #{e.message}"
     ensure
       merge_request.update(in_progress_merge_commit_sha: nil)
     end

changelogs/unreleased-ee/1852-custom-hook-errors-don-t-display-in-merge-request-widget.yml

+---
+title: Show hook errors for fast-forward merges
+merge_request: 1375
+author:

spec/services/merge_requests/ff_merge_service_spec.rb

@@ -16,7 +16,7 @@ describe MergeRequests::FfMergeService do
     project.team << [user2, :developer]
   end
 
-  describe :execute do
+  describe '#execute' do
     context 'valid params' do
       let(:service) { MergeRequests::FfMergeService.new(project, user, {}) }
 
@@ -48,5 +48,37 @@ describe MergeRequests::FfMergeService do
         expect(note.note).to include 'merged'
       end
     end
+
+    context "error handling" do
+      let(:service) { MergeRequests::FfMergeService.new(project, user, commit_message: 'Awesome message') }
+
+      before do
+        allow(Rails.logger).to receive(:error)
+      end
+
+      it 'logs and saves error if there is an exception' do
+        error_message = 'error message'
+
+        allow(service).to receive(:repository).and_raise("error message")
+        allow(service).to receive(:execute_hooks)
+
+        service.execute(merge_request)
+
+        expect(merge_request.merge_error).to include(error_message)
+        expect(Rails.logger).to have_received(:error).with(a_string_matching(error_message))
+      end
+
+      it 'logs and saves error if there is an PreReceiveError exception' do
+        error_message = 'error message'
+
+        allow(service).to receive(:repository).and_raise(GitHooksService::PreReceiveError, error_message)
+        allow(service).to receive(:execute_hooks)
+
+        service.execute(merge_request)
+
+        expect(merge_request.merge_error).to include(error_message)
+        expect(Rails.logger).to have_received(:error).with(a_string_matching(error_message))
+      end
+    end
   end
 end