Merge branch '19092-fix-event-for-legacydiffnote-not-considered-note' into 'master'

Fix diff comments not showing up in activity feed

## What does this MR do?

It fixes the detection of note events to check for `Note` and `LegacyDiffNote`.

## Are there points in the code the reviewer needs to double check?

No? /cc @DouweM (since I believe you introduced `LegacyDiffNote`

## Why was this MR needed?

To fix #19092.

## What are the relevant issue numbers?

Fixes #19092.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5069
(cherry picked from commit b5b17d00)

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.9.5
+  - Fix diff comments not showing up in activity feed. !5069
   - Add index on both Award Emoji user and name. !5061
   - Downgrade to Redis 3.2.2 due to massive memory leak with Sidekiq. !5056
   - Re-enable import button when import process fails due to namespace already being taken. !5053

app/models/event.rb

@@ -67,7 +67,7 @@ class Event < ActiveRecord::Base
     elsif issue? || issue_note?
       Ability.abilities.allowed?(user, :read_issue, note? ? note_target : target)
     else
-      ((merge_request? || note?) && target) || milestone?
+      ((merge_request? || note?) && target.present?) || milestone?
     end
   end
 
@@ -136,7 +136,7 @@ class Event < ActiveRecord::Base
   end
 
   def note?
-    target_type == "Note"
+    target.is_a?(Note)
   end
 
   def issue?

spec/models/event_spec.rb

@@ -46,6 +46,22 @@ describe Event, models: true do
     it { expect(@event.author).to eq(@user) }
   end
 
+  describe '#note?' do
+    subject { Event.new(project: target.project, target: target) }
+
+    context 'issue note event' do
+      let(:target) { create(:note_on_issue) }
+
+      it { is_expected.to be_note }
+    end
+
+    context 'merge request diff note event' do
+      let(:target) { create(:note_on_merge_request_diff) }
+
+      it { is_expected.to be_note }
+    end
+  end
+
   describe '#visible_to_user?' do
     let(:project) { create(:empty_project, :public) }
     let(:non_member) { create(:user) }
@@ -89,7 +105,7 @@ describe Event, models: true do
       end
     end
 
-    context 'note event' do
+    context 'issue note event' do
       context 'on non confidential issues' do
         let(:target) { note_on_issue }
 
@@ -112,6 +128,20 @@ describe Event, models: true do
         it { expect(event.visible_to_user?(admin)).to eq true }
       end
     end
+
+    context 'merge request diff note event' do
+      let(:project) { create(:project, :public) }
+      let(:merge_request) { create(:merge_request, source_project: project, author: author, assignee: assignee) }
+      let(:note_on_merge_request) { create(:note_on_merge_request_diff, noteable: merge_request, project: project) }
+      let(:target) { note_on_merge_request }
+
+      it { expect(event.visible_to_user?(non_member)).to eq true }
+      it { expect(event.visible_to_user?(author)).to eq true }
+      it { expect(event.visible_to_user?(assignee)).to eq true }
+      it { expect(event.visible_to_user?(member)).to eq true }
+      it { expect(event.visible_to_user?(guest)).to eq true }
+      it { expect(event.visible_to_user?(admin)).to eq true }
+    end
   end
 
   describe '.limit_recent' do