Avoid 409 StaleObjectError errors with /rebase

If a merge request is closed, the quick action /rebase will quietly fail
with a 409 StaleObjectError. To avoid that, we disable this quick action
if the merge request is closed.

If a rebase is in progress, the quick action will also fail with the
same error. We now check the state and report to the user that the
rebase is in progress.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/296223

changelogs/unreleased/sh-rebase-quick-action-feedback.yml

+---
+title: Avoid 409 StaleObjectError errors with /rebase
+merge_request: 50719
+author:
+type: fixed

lib/gitlab/quick_actions/merge_request_actions.rb

@@ -48,6 +48,7 @@ module Gitlab
         condition do
           merge_request = quick_action_target
 
+          next false unless merge_request.open?
           next false unless merge_request.source_branch_exists?
 
           access_check = ::Gitlab::UserAccess
@@ -56,6 +57,11 @@ module Gitlab
           access_check.can_push_to_branch?(merge_request.source_branch)
         end
         command :rebase do
+          if quick_action_target.rebase_in_progress?
+            @execution_message[:rebase] = _('A rebase is already in progress.')
+            next
+          end
+
           # This will be used to avoid simultaneous "/merge" and "/rebase" actions
           @updates[:rebase] = true
 

locale/gitlab.pot

@@ -1322,6 +1322,9 @@ msgstr ""
 msgid "A ready-to-go template for use with iOS Swift apps"
 msgstr ""
 
+msgid "A rebase is already in progress."
+msgstr ""
+
 msgid "A regular expression that will be used to find the test coverage output in the job log. Leave blank to disable"
 msgstr ""
 

spec/support/shared_examples/quick_actions/merge_request/rebase_quick_action_shared_examples.rb

@@ -36,6 +36,33 @@ RSpec.shared_examples 'rebase quick action' do
 
         expect(page).to have_content "Scheduled a rebase of branch #{merge_request.source_branch}."
       end
+
+      context 'when the merge request is closed' do
+        before do
+          merge_request.close!
+        end
+
+        it 'does not rebase the MR', :sidekiq_inline do
+          add_note("/rebase")
+
+          expect(page).not_to have_content 'Scheduled a rebase'
+        end
+      end
+
+      context 'when a rebase is in progress', :sidekiq_inline, :clean_gitlab_redis_shared_state do
+        before do
+          jid = SecureRandom.hex
+          merge_request.update!(rebase_jid: jid)
+          Gitlab::SidekiqStatus.set(jid)
+        end
+
+        it 'tells the user a rebase is in progress' do
+          add_note('/rebase')
+
+          expect(page).to have_content 'A rebase is already in progress.'
+          expect(page).not_to have_content 'Scheduled a rebase'
+        end
+      end
     end
 
     context 'when the current user cannot rebase the MR' do
@@ -48,7 +75,7 @@ RSpec.shared_examples 'rebase quick action' do
       it 'does not rebase the MR' do
         add_note("/rebase")
 
-        expect(page).not_to have_content 'Your commands have been executed!'
+        expect(page).not_to have_content 'Scheduled a rebase'
       end
     end
   end