Merge branch '19702-define_show_html_vars' into 'master'

Be explicit on merge request discussion variables

## What does this MR do?

To avoid conditionals and to messing with request.format and accept headers to know in which format we're going to response I've decided to be explicit in when we need the discussion variables

## Why was this MR needed?

Solve a bug https://sentry.gitlap.com/gitlab/staginggitlabcom/issues/8492/

## What are the relevant issue numbers?

Closes #19702 

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- ~~[ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~[ ] API support added~~
- Tests
  - [ ] 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 !5204

3 files changed, 41 insertions, 10 deletions

diff --git a/CHANGELOG b/CHANGELOG
index d2e275ff6f5..f12f6423c7a 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -56,6 +56,7 @@ v 8.10.0 (unreleased)
   - Add API endpoint for a group issues !4520 (mahcsig)
   - Add Bugzilla integration !4930 (iamtjg)
   - Instrument Rinku usage
+  - Be explicit to define merge request discussion variables
   - Metrics for Rouge::Plugins::Redcarpet and Rouge::Formatters::HTMLGitlab
   - RailsCache metris now includes fetch_hit/fetch_miss and read_hit/read_miss info.
   - Allow [ci skip] to be in any case and allow [skip ci]. !4785 (simon_w)
diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index 941d68cda17..df659bb8c3b 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -56,7 +56,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
 
   def show
     respond_to do |format|
-      format.html
+      format.html { define_discussion_vars }
 
       format.json do
         render json: @merge_request
@@ -82,7 +82,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     @merge_request_diff = @merge_request.merge_request_diff
 
     respond_to do |format|
-      format.html
+      format.html { define_discussion_vars }
       format.json { render json: { html: view_to_html_string("projects/merge_requests/show/_diffs") } }
     end
   end
@@ -108,7 +108,11 @@ class Projects::MergeRequestsController < Projects::ApplicationController
 
   def commits
     respond_to do |format|
-      format.html { render 'show' }
+      format.html do
+        define_discussion_vars
+
+        render 'show'
+      end
       format.json do
         # Get commits from repository
         # or from cache if already merged
@@ -123,7 +127,11 @@ class Projects::MergeRequestsController < Projects::ApplicationController
 
   def builds
     respond_to do |format|
-      format.html { render 'show' }
+      format.html do
+        define_discussion_vars
+
+        render 'show'
+      end
       format.json { render json: { html: view_to_html_string('projects/merge_requests/show/_builds') } }
     end
   end
@@ -353,14 +361,11 @@ class Projects::MergeRequestsController < Projects::ApplicationController
       @merge_request.unlock_mr
       @merge_request.close
     end
-
-    if request.format == :html || action_name == 'show'
-      define_show_html_vars
-    end
   end
 
-  # Discussion tab data is only required on html requests
-  def define_show_html_vars
+  # Discussion tab data is rendered on html responses of actions
+  # :show, :diff, :commits, :builds. but not when request the data through AJAX
+  def define_discussion_vars
     # Build a note object for comment form
     @note = @project.notes.new(noteable: @noteable)
 
diff --git a/spec/features/merge_requests/diffs_spec.rb b/spec/features/merge_requests/diffs_spec.rb
new file mode 100644
index 00000000000..c9a0059645d
--- /dev/null
+++ b/spec/features/merge_requests/diffs_spec.rb
@@ -0,0 +1,25 @@
+require 'spec_helper'
+
+feature 'Diffs URL', js: true, feature: true do
+  before do
+    login_as :admin
+    @merge_request = create(:merge_request)
+    @project = @merge_request.source_project
+  end
+
+  context 'when visit with */* as accept header' do
+    before(:each) do
+      page.driver.add_header('Accept', '*/*')
+    end
+
+    it 'renders the notes' do
+      create :note_on_merge_request, project: @project, noteable: @merge_request, note: 'Rebasing with master'
+
+      visit diffs_namespace_project_merge_request_path(@project.namespace, @project, @merge_request)
+
+      # Load notes and diff through AJAX
+      expect(page).to have_css('.note-text', visible: false, text: 'Rebasing with master')
+      expect(page).to have_css('.diffs.tab-pane.active')
+    end
+  end
+end