Add a quick action for /rebase

This will make it easier for people to bring their merge requests
up-to-date.

lib/gitlab/quick_actions/merge_request_actions.rb

@@ -38,6 +38,37 @@ module Gitlab
           @updates[:merge] = params[:merge_request_diff_head_sha]
         end
 
+        types MergeRequest
+        desc do
+          _('Rebase source branch')
+        end
+        explanation do
+          _('Rebase source branch on the target branch.')
+        end
+        condition do
+          merge_request = quick_action_target
+
+          next false unless merge_request.source_branch_exists?
+
+          access_check = ::Gitlab::UserAccess
+                           .new(current_user, container: merge_request.source_project)
+
+          access_check.can_push_to_branch?(merge_request.source_branch)
+        end
+        command :rebase do
+          result = MergeRequests::RebaseService.new(quick_action_target.project, current_user)
+                      .execute(quick_action_target)
+
+          branch = quick_action_target.source_branch
+
+          @execution_message[:rebase] =
+            if result[:status] == :success
+              _('Scheduled a rebase of branch %{branch}.')
+            else
+              _('Failed to schedule a rebase of %{branch}.')
+            end % { branch: branch }
+        end
+
         desc 'Toggle the Draft status'
         explanation do
           noun = quick_action_target.to_ability_name.humanize(capitalize: false)

locale/gitlab.pot

@@ -11880,6 +11880,9 @@ msgstr ""
 msgid "Failed to save preferences."
 msgstr ""
 
+msgid "Failed to schedule a rebase of %{branch}."
+msgstr ""
+
 msgid "Failed to set due date because the date format is invalid."
 msgstr ""
 
@@ -22975,6 +22978,12 @@ msgstr ""
 msgid "Rebase in progress"
 msgstr ""
 
+msgid "Rebase source branch"
+msgstr ""
+
+msgid "Rebase source branch on the target branch."
+msgstr ""
+
 msgid "Receive alerts from manually configured Prometheus servers."
 msgstr ""
 
@@ -24328,6 +24337,9 @@ msgstr ""
 msgid "Scheduled Deletion At - %{permanent_deletion_time}"
 msgstr ""
 
+msgid "Scheduled a rebase of branch %{branch}."
+msgstr ""
+
 msgid "Scheduled to merge this merge request (%{strategy})."
 msgstr ""
 

spec/features/merge_request/user_uses_quick_actions_spec.rb

@@ -41,5 +41,6 @@ RSpec.describe 'Merge request > User uses quick actions', :js do
     end
 
     it_behaves_like 'merge quick action'
+    it_behaves_like 'rebase quick action'
   end
 end

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

+# frozen_string_literal: true
+
+RSpec.shared_examples 'rebase quick action' do
+  context 'when updating the description' do
+    before do
+      sign_in(user)
+      visit edit_project_merge_request_path(project, merge_request)
+    end
+
+    it 'rebases the MR', :sidekiq_inline do
+      fill_in('Description', with: '/rebase')
+      click_button('Save changes')
+
+      expect(page).not_to have_content('commit behind the target branch')
+      expect(merge_request.reload).not_to be_merged
+    end
+  end
+
+  context 'when creating a new note' do
+    context 'when the current user can rebase the MR' do
+      before do
+        sign_in(user)
+        visit project_merge_request_path(project, merge_request)
+      end
+
+      it 'rebase the MR', :sidekiq_inline do
+        add_note("/rebase")
+
+        expect(page).to have_content "Scheduled a rebase of branch #{merge_request.source_branch}."
+      end
+    end
+
+    context 'when the current user cannot rebase the MR' do
+      before do
+        project.add_guest(guest)
+        sign_in(guest)
+        visit project_merge_request_path(project, merge_request)
+      end
+
+      it 'does not rebase the MR' do
+        add_note("/rebase")
+
+        expect(page).not_to have_content 'Your commands have been executed!'
+      end
+    end
+  end
+end