Merge branch 'sh-fix-issue-33011' into 'master'

Fix Error 500 when viewing a merge request with a deleted source project

Closes gitlab-ce#33011

See merge request !1996

app/presenters/merge_request_presenter.rb

@@ -182,6 +182,8 @@ class MergeRequestPresenter < Gitlab::View::Presenter::Delegated
   end
 
   def user_can_push_to_source_branch?
+    return false unless source_branch_exists?
+
     ::Gitlab::UserAccess
       .new(current_user, project: source_project)
       .can_push_to_branch?(source_branch)

spec/presenters/merge_request_presenter_spec.rb

@@ -443,6 +443,10 @@ describe MergeRequestPresenter do
       let(:can_push_to_branch) { true }
       let(:should_be_rebased) { true }
 
+      before do
+        allow(resource).to receive(:source_branch_exists?) { true }
+      end
+
       it 'returns path' do
         is_expected
           .to eq("/#{project.full_path}/merge_requests/#{resource.iid}/rebase")

spec/serializers/merge_request_entity_spec.rb

@@ -146,4 +146,20 @@ describe MergeRequestEntity do
       end
     end
   end
+
+  describe 'when source project is deleted' do
+    let(:project) { create(:project, :repository) }
+    let(:fork_project) { create(:project, :repository, forked_from_project: project) }
+    let(:merge_request) { create(:merge_request, source_project: fork_project, target_project: project) }
+
+    it 'returns a blank rebase_path' do
+      allow(merge_request).to receive(:should_be_rebased?).and_return(true)
+      fork_project.destroy
+      merge_request.reload
+
+      entity = described_class.new(merge_request, request: request).as_json
+
+      expect(entity[:rebase_path]).to be_nil
+    end
+  end
 end