Only cache highlight results for latest MR diffs

Previously, we kept them all in the cache. We don't need the highlight results
for older diffs - if someone does view that (which is rare), we can do the
highlighting on the fly.

1 files changed, 10 insertions, 1 deletions

diff --git a/app/services/merge_requests/merge_request_diff_cache_service.rb b/app/services/merge_requests/merge_request_diff_cache_service.rb
index 2945a7fd4e4..10aa9ae609c 100644
--- a/app/services/merge_requests/merge_request_diff_cache_service.rb
+++ b/app/services/merge_requests/merge_request_diff_cache_service.rb
@@ -1,8 +1,17 @@
 module MergeRequests
   class MergeRequestDiffCacheService
-    def execute(merge_request)
+    def execute(merge_request, new_diff)
       # Executing the iteration we cache all the highlighted diff information
       merge_request.diffs.diff_files.to_a
+
+      # Remove cache for all diffs on this MR. Do not use the association on the
+      # model, as that will interfere with other actions happening when
+      # reloading the diff.
+      MergeRequestDiff.where(merge_request: merge_request).each do |merge_request_diff|
+        next if merge_request_diff == new_diff
+
+        merge_request_diff.diffs.clear_cache!
+      end
     end
   end
 end