Fix Lint errors

  Add localization in gitlab.pot
  Fix various lint errors and messages

app/models/diff_note.rb

@@ -39,13 +39,16 @@ class DiffNote < Note
     return unless should_create_diff_file?
 
     diff_file = fetch_diff_file
-    raise  NoteDiffFileCreationError, DIFF_FILE_NOT_FOUND_MESSAGE unless diff_file
+    raise NoteDiffFileCreationError, DIFF_FILE_NOT_FOUND_MESSAGE unless diff_file
+
     diff_line = diff_file.line_for_position(self.original_position)
-    raise  NoteDiffFileCreationError,  DIFF_LINE_NOT_FOUND_MESSAGE % {
-        file_path: diff_file.file_path,
-        new_pos: original_position.new_line,
-        old_pos: original_position.old_line
-    } unless diff_line
+    unless diff_line
+      raise NoteDiffFileCreationError, DIFF_LINE_NOT_FOUND_MESSAGE % {
+          file_path: diff_file.file_path,
+          new_pos: original_position.new_line,
+          old_pos: original_position.old_line
+      }
+    end
 
     creation_params = diff_file.diff.to_hash
       .except(:too_large)
@@ -121,6 +124,7 @@ class DiffNote < Note
 
   def fetch_diff_file
     return note_diff_file.raw_diff_file if note_diff_file
+
     if created_at_diff?(noteable.diff_refs)
       # We're able to use the already persisted diffs (Postgres) if we're
       # presenting a "current version" of the MR discussion diff.
@@ -132,6 +136,7 @@ class DiffNote < Note
       # if line is not found in persisted diffs, fallback and retrieve file from repository using gitaly
       file = nil if file&.line_for_position(original_position).nil? && importing?
     end
+
     file ||= original_position.diff_file(repository)
     file&.unfold_diff_lines(position)
 

locale/gitlab.pot

@@ -7373,6 +7373,12 @@ msgstr ""
 msgid "Failed to enqueue the rebase operation, possibly due to a long-lived transaction. Try again later."
 msgstr ""
 
+msgid "Failed to find diff file"
+msgstr ""
+
+msgid "Failed to find diff line for: %{file_path}, new_pos: %{new_pos}, old_pos: %{old_pos}"
+msgstr ""
+
 msgid "Failed to get ref."
 msgstr ""
 

spec/models/diff_note_spec.rb

@@ -91,7 +91,6 @@ describe DiffNote do
   end
 
   describe '#create_diff_file callback' do
-
     context 'merge request' do
       let(:position) do
         Gitlab::Diff::Position.new(old_path: "files/ruby/popen.rb",
@@ -101,6 +100,7 @@ describe DiffNote do
                                    diff_refs: merge_request.diff_refs)
       end
       subject { build(:diff_note_on_merge_request, project: project, position: position, noteable: merge_request) }
+
       let(:diff_file_from_repository) do
         position.diff_file(project.repository)
       end
@@ -168,7 +168,6 @@ describe DiffNote do
                 subject.save
                 expect(subject.reload.note_diff_file).to be_present
               end
-
             end
           end
         end
@@ -189,7 +188,7 @@ describe DiffNote do
       end
 
       it 'does not create diff note file if it is a reply' do
-        diff_note =  create(:diff_note_on_merge_request, project: project, noteable: merge_request)
+        diff_note = create(:diff_note_on_merge_request, project: project, noteable: merge_request)
         expect { create(:diff_note_on_merge_request, noteable: merge_request, in_reply_to: diff_note) }
           .not_to change(NoteDiffFile, :count)
       end

spec/support/shared_examples/models/diff_note_after_commit_shared_examples.rb

 # frozen_string_literal: true
 
 shared_examples 'a valid diff note with after commit callback' do
-
   context 'when diff file is fetched from repository' do
     before do
       allow_any_instance_of(::Gitlab::Diff::Position).to receive(:diff_file).with(project.repository).and_return(diff_file_from_repository)
@@ -31,7 +30,6 @@ shared_examples 'a valid diff note with after commit callback' do
         subject.save
         expect(subject.reload.note_diff_file).to be_present
       end
-
     end
   end