Speedup DiffNote#active? on discussions, preloading noteables and avoid touching git repository to return diff_refs when possible

- Preloading noteable we share the same noteable instance when more than one 
discussion refers to the same noteable.
- Any other call to that object that is cached in that object will be for any 
discussion.
- In those cases where merge_request_diff has all the sha stored to build a diff_refs get that 
diff_refs using directly those sha instead accessing to the git repository to first get the 
commits and later the sha.

1 files changed, 10 insertions, 2 deletions

diff --git a/app/models/diff_note.rb b/app/models/diff_note.rb
index 9671955db36..c816deb4e0c 100644
--- a/app/models/diff_note.rb
+++ b/app/models/diff_note.rb
@@ -67,7 +67,7 @@ class DiffNote < Note
     return false unless supported?
     return true if for_commit?
 
-    diff_refs ||= self.noteable.diff_refs
+    diff_refs ||= noteable_diff_refs
 
     self.position.diff_refs == diff_refs
   end
@@ -78,6 +78,14 @@ class DiffNote < Note
     !self.for_merge_request? || self.noteable.support_new_diff_notes?
   end
 
+  def noteable_diff_refs
+    if noteable.respond_to?(:diff_sha_refs)
+      noteable.diff_sha_refs
+    else
+      noteable.diff_refs
+    end
+  end
+
   def set_original_position
     self.original_position = self.position.dup
   end
@@ -96,7 +104,7 @@ class DiffNote < Note
       self.project,
       nil,
       old_diff_refs: self.position.diff_refs,
-      new_diff_refs: self.noteable.diff_refs,
+      new_diff_refs: noteable_diff_refs,
       paths: self.position.paths
     ).execute(self)
   end