Avoid 500's when serializing legacy diff notes

2 files changed, 14 insertions, 0 deletions

diff --git a/lib/gitlab/diff/file_collection/base.rb b/lib/gitlab/diff/file_collection/base.rb
index 10df037a0dd..c5bbf522f7c 100644
--- a/lib/gitlab/diff/file_collection/base.rb
+++ b/lib/gitlab/diff/file_collection/base.rb
@@ -34,6 +34,16 @@ module Gitlab
           @diff_files ||= diffs.decorate! { |diff| decorate_diff!(diff) }
         end
 
+        # This mutates `diff_files` lines.
+        def unfold_diff_files(positions)
+          positions_grouped_by_path = positions.group_by { |position| position.file_path }
+
+          diff_files.each do |diff_file|
+            positions = positions_grouped_by_path.fetch(diff_file.file_path, [])
+            positions.each { |position| diff_file.unfold_diff_lines(position) }
+          end
+        end
+
         def diff_file_with_old_path(old_path)
           diff_files.find { |diff_file| diff_file.old_path == old_path }
         end
diff --git a/lib/gitlab/diff/file_collection/compare.rb b/lib/gitlab/diff/file_collection/compare.rb
index 586c5cf87af..663bad95db7 100644
--- a/lib/gitlab/diff/file_collection/compare.rb
+++ b/lib/gitlab/diff/file_collection/compare.rb
@@ -10,6 +10,10 @@ module Gitlab
             diff_options: diff_options,
             diff_refs:    diff_refs)
         end
+
+        def unfold_diff_lines(positions)
+          # no-op
+        end
       end
     end
   end