Change the way totalNotes is calculated

totalNotes is only used to prerender a number of
skeleton containers until real notes are loaded

issuable.discussions makes multiple requests, so
too expensive for this

This commit uses mere notes for this and sends
actual totalNotes number if it's less than 10;
otherwise it sends 10 - it allows us to avoid
bunch of skeleton prerenderings, which are not
necessary since they doesn't fit into the whole
screen and disappear quite fast

app/assets/javascripts/notes/components/notes_app.vue

@@ -75,9 +75,9 @@ export default {
     },
     allDiscussions() {
       if (this.isLoading) {
-        const totalNotes = parseInt(this.notesData.totalNotes, 10) || 0;
+        const prerenderedNotesCount = parseInt(this.notesData.prerenderedNotesCount, 10) || 0;
 
-        return new Array(totalNotes).fill({
+        return new Array(prerenderedNotesCount).fill({
           isSkeletonNote: true,
         });
       }

app/helpers/notes_helper.rb

 # frozen_string_literal: true
 
 module NotesHelper
+  MAX_PRERENDERED_NOTES = 10
+
   def note_target_fields(note)
     if note.noteable
       hidden_field_tag(:target_type, note.noteable.class.name.underscore) +
@@ -169,7 +171,7 @@ module NotesHelper
       closePath: close_issuable_path(issuable),
       reopenPath: reopen_issuable_path(issuable),
       notesPath: notes_url,
-      totalNotes: issuable.discussions.length,
+      prerenderedNotesCount: issuable.capped_notes_count(MAX_PRERENDERED_NOTES),
       lastFetchedAt: Time.now.to_i
     }
   end

app/models/concerns/noteable.rb

@@ -73,6 +73,10 @@ module Noteable
       .discussions(self)
   end
 
+  def capped_notes_count(max)
+    notes.limit(max).count
+  end
+
   def grouped_diff_discussions(*args)
     # Doesn't use `discussion_notes`, because this may include commit diff notes
     # besides MR diff notes, that we do not want to display on the MR Changes tab.

spec/javascripts/notes/mock_data.js

@@ -8,7 +8,7 @@ export const notesDataMock = {
   notesPath: '/gitlab-org/gitlab-ce/noteable/issue/98/notes',
   quickActionsDocsPath: '/help/user/project/quick_actions',
   registerPath: '/users/sign_in?redirect_to_referer=yes#register-pane',
-  totalNotes: 1,
+  prerenderedNotesCount: 1,
   closePath: '/twitter/flight/issues/9.json?issue%5Bstate_event%5D=close',
   reopenPath: '/twitter/flight/issues/9.json?issue%5Bstate_event%5D=reopen',
   canAwardEmoji: true,

spec/models/concerns/noteable_spec.rb

@@ -272,4 +272,22 @@ describe Noteable do
       expect(described_class.resolvable_types).to include('MergeRequest')
     end
   end
+
+  describe '#capped_notes_count' do
+    context 'notes number < 10' do
+      it 'the number of notes is returned' do
+        expect(subject.capped_notes_count(10)).to eq(9)
+      end
+    end
+
+    context 'notes number > 10' do
+      before do
+        create_list(:note, 2, project: project, noteable: subject)
+      end
+
+      it '10 is returned' do
+        expect(subject.capped_notes_count(10)).to eq(10)
+      end
+    end
+  end
 end