Always read diff_view setting from the cookie

Prior, when the user had their view set to "parallel" and then visited a
merge request's changes tab _without_ passing the `view` parameter via
query string, the view would be parallel but the `Notes` class was
always instantiated with the default value from `diff_view` ("inline"),
resulting in broken markup when the form to add a line note was
dynamically inserted.

The cookie is set whenever the view is changed, so this value should
always be up-to-date.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14557

1 files changed, 7 insertions, 1 deletions

diff --git a/app/helpers/diff_helper.rb b/app/helpers/diff_helper.rb
index 6a3ec83b8c0..97466d532f4 100644
--- a/app/helpers/diff_helper.rb
+++ b/app/helpers/diff_helper.rb
@@ -9,7 +9,13 @@ module DiffHelper
   end
 
   def diff_view
-    params[:view] == 'parallel' ? 'parallel' : 'inline'
+    diff_views = %w(inline parallel)
+
+    if diff_views.include?(cookies[:diff_view])
+      cookies[:diff_view]
+    else
+      diff_views.first
+    end
   end
 
   def diff_hard_limit_enabled?