Memoize the maximum access level for the author of notes

In #19273, we saw that retrieving ProjectTeam#human_max_access for each
note takes the bulk of the time when rendering certain issues or merge requests.
We observe that most of the comments in an issue are typically done by the
same users. This MR memoizes the max access level by user ID.

app/helpers/notes_helper.rb

@@ -69,4 +69,12 @@ module NotesHelper
     button_tag 'Reply...', class: 'btn btn-text-field js-discussion-reply-button',
                            data: data, title: 'Add a reply'
   end
+
+  def note_max_access_for_user(note)
+    user_id = note.author.id
+    project = note.project
+    @max_access_by_user_id ||= Hash.new { |hash, key| hash[key] = project.team.human_max_access(key) }
+
+    @max_access_by_user_id[user_id]
+  end
 end

app/views/projects/notes/_note.html.haml

@@ -17,7 +17,7 @@
           %a{ href: "##{dom_id(note)}" }
             = time_ago_with_tooltip(note.created_at, placement: 'bottom', html_class: 'note-created-ago')
         .note-actions
-          - access = note.project.team.human_max_access(note.author.id)
+          - access = note_max_access_for_user(note)
           - if access and not note.system
             %span.note-role.hidden-xs= access
           - if current_user and not note.system

spec/helpers/notes_helper_spec.rb

@@ -0,0 +1,32 @@
+require "spec_helper"
+
+describe NotesHelper do
+  describe "#notes_max_access_for_users" do
+    let(:owner) { create(:owner) }
+    let(:group) { create(:group) }
+    let(:project) { create(:empty_project, namespace: group) }
+    let(:master) { create(:user) }
+    let(:reporter) { create(:user) }
+    let(:guest) { create(:user) }
+
+    let(:owner_note) { create(:note, author: owner, project: project) }
+    let(:master_note) { create(:note, author: master, project: project) }
+    let(:reporter_note) { create(:note, author: reporter, project: project) }
+    let!(:notes) { [owner_note, master_note, reporter_note] }
+
+    before do
+      group.add_owner(owner)
+      project.team << [master, :master]
+      project.team << [reporter, :reporter]
+      project.team << [guest, :guest]
+    end
+
+    it 'return human access levels' do
+      expect(helper.note_max_access_for_user(owner_note)).to eq('Owner')
+      expect(helper.note_max_access_for_user(master_note)).to eq('Master')
+      expect(helper.note_max_access_for_user(reporter_note)).to eq('Reporter')
+      # Call it again to ensure value is cached
+      expect(helper.note_max_access_for_user(owner_note)).to eq('Owner')
+    end
+  end
+end