Don't create a temp reference for branch comparisons within project

A temp reference is only needed to fetch a branch from another project,
as in the case for forked repositories. For branch comparisons within
the same project, we can just use the existing branch names to do the
comparison.

Relates to https://gitlab.com/gitlab-org/gitlab-ce/issues/38689#note_126107862

1 files changed, 36 insertions, 0 deletions

diff --git a/spec/lib/gitlab/git/repository_spec.rb b/spec/lib/gitlab/git/repository_spec.rb
index 778950c95e4..85c45ea4183 100644
--- a/spec/lib/gitlab/git/repository_spec.rb
+++ b/spec/lib/gitlab/git/repository_spec.rb
@@ -1966,6 +1966,42 @@ describe Gitlab::Git::Repository, :seed_helper do
     end
   end
 
+  describe '#compare_source_branch' do
+    context 'within same repository' do
+      it 'does not create a temp ref' do
+        expect(repository).not_to receive(:fetch_source_branch!)
+        expect(repository).not_to receive(:delete_refs)
+
+        compare = repository.compare_source_branch('master', repository, 'feature', straight: false)
+        expect(compare).to be_a(Gitlab::Git::Compare)
+        expect(compare.commits.count).to be > 0
+      end
+
+      it 'returns nil when source ref does not exist' do
+        compare = repository.compare_source_branch('master', repository, 'non-existent-branch', straight: false)
+
+        expect(compare).to be_nil
+      end
+    end
+
+    context 'with different repositories' do
+      it 'creates a temp ref' do
+        expect(repository).to receive(:fetch_source_branch!).and_call_original
+        expect(repository).to receive(:delete_refs).and_call_original
+
+        compare = repository.compare_source_branch('master', mutable_repository, 'feature', straight: false)
+        expect(compare).to be_a(Gitlab::Git::Compare)
+        expect(compare.commits.count).to be > 0
+      end
+
+      it 'returns nil when source ref does not exist' do
+        compare = repository.compare_source_branch('master', mutable_repository, 'non-existent-branch', straight: false)
+
+        expect(compare).to be_nil
+      end
+    end
+  end
+
   describe '#checksum' do
     it 'calculates the checksum for non-empty repo' do
       expect(repository.checksum).to eq '51d0a9662681f93e1fee547a6b7ba2bcaf716059'