Fetch merge request ref if it is missing when visit MR page

This will fix merge problem for merge requests between forks created
before 8.0

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 93faa133875..eb468c6cd53 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -433,10 +433,22 @@ class MergeRequest < ActiveRecord::Base
     target_project.repository.fetch_ref(
       source_project.repository.path_to_repo,
       "refs/heads/#{source_branch}",
-      "refs/merge-requests/#{iid}/head"
+      ref_path
     )
   end
 
+  def ref_path
+    "refs/merge-requests/#{iid}/head"
+  end
+
+  def ref_is_fetched?
+    File.exists?(File.join(project.repository.path_to_repo, ref_path))
+  end
+
+  def ensure_ref_fetched
+    fetch_ref unless ref_is_fetched?
+  end
+
   def in_locked_state
     begin
       lock_mr