Store only generic message if rebase fails4020-rebase-message

Instead of storing detailed rebase error, only a generic message is
stored with MR. The reason is that this message is exposed and displayed
to end user and there is no reason to expose detailed backend
information. Error message is still logged so detailed information
can be found in logfile by admin if needed.

Related #41820

3 files changed, 17 insertions, 10 deletions

diff --git a/app/services/merge_requests/rebase_service.rb b/app/services/merge_requests/rebase_service.rb
index 0d5a25fa28e..c0083cd6afd 100644
--- a/app/services/merge_requests/rebase_service.rb
+++ b/app/services/merge_requests/rebase_service.rb
@@ -1,12 +1,14 @@
 module MergeRequests
   class RebaseService < MergeRequests::WorkingCopyBaseService
+    REBASE_ERROR = 'Rebase failed. Please rebase locally'.freeze
+
     def execute(merge_request)
       @merge_request = merge_request
 
       if rebase
         success
       else
-        error('Failed to rebase. Should be done manually')
+        error(REBASE_ERROR)
       end
     end
 
@@ -22,8 +24,8 @@ module MergeRequests
 
       true
     rescue => e
-      log_error('Failed to rebase branch:')
-      log_error(e.message, save_message_on_model: true)
+      log_error(REBASE_ERROR, save_message_on_model: true)
+      log_error(e.message)
       false
     end
   end
diff --git a/changelogs/unreleased/4020-rebase-message.yml b/changelogs/unreleased/4020-rebase-message.yml
new file mode 100644
index 00000000000..4793f3d9cb9
--- /dev/null
+++ b/changelogs/unreleased/4020-rebase-message.yml
@@ -0,0 +1,5 @@
+---
+title: Display user friendly error message if rebase fails.
+merge_request:
+author:
+type: fixed
diff --git a/spec/services/merge_requests/rebase_service_spec.rb b/spec/services/merge_requests/rebase_service_spec.rb
index d1b37cdd073..5f047e61c31 100644
--- a/spec/services/merge_requests/rebase_service_spec.rb
+++ b/spec/services/merge_requests/rebase_service_spec.rb
@@ -32,7 +32,7 @@ describe MergeRequests::RebaseService do
 
       it 'returns an error' do
         expect(service.execute(merge_request)).to match(status: :error,
-                                                        message: 'Failed to rebase. Should be done manually')
+                                                        message: described_class::REBASE_ERROR)
       end
     end
 
@@ -41,15 +41,15 @@ describe MergeRequests::RebaseService do
         allow(repository).to receive(:run_git!).and_raise('Something went wrong')
       end
 
-      it 'saves the error message' do
+      it 'saves a generic error message' do
         subject.execute(merge_request)
 
-        expect(merge_request.reload.merge_error).to eq 'Something went wrong'
+        expect(merge_request.reload.merge_error).to eq described_class::REBASE_ERROR
       end
 
       it 'returns an error' do
         expect(service.execute(merge_request)).to match(status: :error,
-                                                        message: 'Failed to rebase. Should be done manually')
+                                                        message: described_class::REBASE_ERROR)
       end
     end
 
@@ -58,15 +58,15 @@ describe MergeRequests::RebaseService do
         allow(repository).to receive(:run_git!).and_raise(Gitlab::Git::Repository::GitError, 'Something went wrong')
       end
 
-      it 'saves the error message' do
+      it 'saves a generic error message' do
         subject.execute(merge_request)
 
-        expect(merge_request.reload.merge_error).to eq 'Something went wrong'
+        expect(merge_request.reload.merge_error).to eq described_class::REBASE_ERROR
       end
 
       it 'returns an error' do
         expect(service.execute(merge_request)).to match(status: :error,
-                                                        message: 'Failed to rebase. Should be done manually')
+                                                        message: described_class::REBASE_ERROR)
       end
     end