Cache diff highlight in discussions

This commit handles note diffs caching, which considerably improves
the performance on merge requests with lots of comments.
Important to note that the caching approach taken here is different
from `Gitlab::Diff::HighlightCache`. We do not reset the whole cache
when a new push is sent or anything else. That's because discussions
diffs are persisted and do not change.

1 files changed, 15 insertions, 0 deletions

diff --git a/app/models/note_diff_file.rb b/app/models/note_diff_file.rb
index 27aef7adc48..e369122003e 100644
--- a/app/models/note_diff_file.rb
+++ b/app/models/note_diff_file.rb
@@ -3,7 +3,22 @@
 class NoteDiffFile < ActiveRecord::Base
   include DiffFile
 
+  scope :for_commit_or_unresolved, -> do
+    joins(:diff_note).where("resolved_at IS NULL OR noteable_type = 'Commit'")
+  end
+
+  delegate :original_position, :project, to: :diff_note
+
   belongs_to :diff_note, inverse_of: :note_diff_file
 
   validates :diff_note, presence: true
+
+  def raw_diff_file
+    raw_diff = Gitlab::Git::Diff.new(to_hash)
+
+    Gitlab::Diff::File.new(raw_diff,
+                           repository: project.repository,
+                           diff_refs: original_position.diff_refs,
+                           unique_identifier: id)
+  end
 end