Merge branch '40530-merge-request-generates-wrong-diff-when-branch-and-tag-have-the-same-name' into 'master'

Resolve "Merge request generates wrong diff when branch and tag have the same name"

Closes #40530

See merge request gitlab-org/gitlab-ce!15591

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index a6e7c410bdd..d399636bb28 100644
--- a/lib/gitlab/git/repository.rb
+++ b/lib/gitlab/git/repository.rb
@@ -1046,9 +1046,15 @@ module Gitlab
       end
 
       def with_repo_tmp_commit(start_repository, start_branch_name, sha)
+        source_ref = start_branch_name
+
+        unless Gitlab::Git.branch_ref?(source_ref)
+          source_ref = "#{Gitlab::Git::BRANCH_REF_PREFIX}#{source_ref}"
+        end
+
         tmp_ref = fetch_ref(
           start_repository,
-          source_ref: "#{Gitlab::Git::BRANCH_REF_PREFIX}#{start_branch_name}",
+          source_ref: source_ref,
           target_ref: "refs/tmp/#{SecureRandom.hex}"
         )