Fix expanding a collapsed diff when converting a symlink to a regular file

In this case comparing old_path and new_path is not enough because there
are two entires that match.

2 files changed, 2 insertions, 2 deletions

diff --git a/lib/gitlab/diff/file.rb b/lib/gitlab/diff/file.rb
index ce85e5e0123..5110bfbf898 100644
--- a/lib/gitlab/diff/file.rb
+++ b/lib/gitlab/diff/file.rb
@@ -126,7 +126,7 @@ module Gitlab
         repository.blob_at(commit.id, file_path)
       end
 
-      def cache_key
+      def file_identifier
         "#{file_path}-#{new_file}-#{deleted_file}-#{renamed_file}"
       end
     end
diff --git a/lib/gitlab/diff/file_collection/merge_request_diff.rb b/lib/gitlab/diff/file_collection/merge_request_diff.rb
index dc4d47c878b..fe7adb7bed6 100644
--- a/lib/gitlab/diff/file_collection/merge_request_diff.rb
+++ b/lib/gitlab/diff/file_collection/merge_request_diff.rb
@@ -39,7 +39,7 @@ module Gitlab
         # hashes that represent serialized diff lines.
         #
         def cache_highlight!(diff_file)
-          item_key = diff_file.cache_key
+          item_key = diff_file.file_identifier
 
           if highlight_cache[item_key]
             highlight_diff_file_from_cache!(diff_file, highlight_cache[item_key])