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, 7 insertions, 1 deletions

diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index a22e3c4b9dd..6cebc9ac9eb 100644
--- a/lib/gitlab/git/repository.rb
+++ b/lib/gitlab/git/repository.rb
@@ -732,6 +732,12 @@ module Gitlab
       end
 
       def compare_source_branch(target_branch_name, source_repository, source_branch_name, straight:)
+        if source_repository == self
+          return unless commit(source_branch_name).present?
+
+          return Gitlab::Git::Compare.new(self, target_branch_name, source_branch_name, straight: straight)
+        end
+
         tmp_ref = "refs/tmp/#{SecureRandom.hex}"
 
         return unless fetch_source_branch!(source_repository, source_branch_name, tmp_ref)
@@ -743,7 +749,7 @@ module Gitlab
           straight: straight
         )
       ensure
-        delete_refs(tmp_ref)
+        delete_refs(tmp_ref) if tmp_ref
       end
 
       def write_ref(ref_path, ref, old_ref: nil)