Avoidp loading merge request diff files when not needed

app/services/merge_requests/reload_diffs_service.rb

@@ -38,7 +38,7 @@ module MergeRequests
       # reloading the diff.
       MergeRequestDiff
         .where(merge_request: merge_request)
-        .preload(:merge_request_diff_files, merge_request: :target_project)
+        .preload(merge_request: :target_project)
         .find_each do |merge_request_diff|
         next if merge_request_diff == new_diff
 

lib/gitlab/diff/file_collection/base.rb

@@ -17,7 +17,6 @@ module Gitlab
 
           @diffable = diffable
           @include_stats = diff_options.delete(:include_stats)
-          @diffs = diffable.raw_diffs(diff_options)
           @project = project
           @diff_options = diff_options
           @diff_refs = diff_refs
@@ -25,8 +24,12 @@ module Gitlab
           @repository = project.repository
         end
 
+        def diffs
+          @diffs ||= diffable.raw_diffs(diff_options)
+        end
+
         def diff_files
-          @diff_files ||= @diffs.decorate! { |diff| decorate_diff!(diff) }
+          @diff_files ||= diffs.decorate! { |diff| decorate_diff!(diff) }
         end
 
         def diff_file_with_old_path(old_path)