Fix no avatar not showing in user selection box

After upgrading to Ruby 2.5.3, we switched `URI.join` in favor of
`Gitlab::Utils.append_path`. However,
ActionController::Base.helpers.image_path can return a full URL if a CDN
host is present.

Rails provides a way to generate the full URL using the asset path, but
that doesn't appear to work because `request` is nil`.

Revert to the previous behavior to handle CDNs and relative URLs.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56268

1 files changed, 9 insertions, 0 deletions

diff --git a/spec/lib/gitlab/gon_helper_spec.rb b/spec/lib/gitlab/gon_helper_spec.rb
index c6f09ca2112..1ff2334bacf 100644
--- a/spec/lib/gitlab/gon_helper_spec.rb
+++ b/spec/lib/gitlab/gon_helper_spec.rb
@@ -29,4 +29,13 @@ describe Gitlab::GonHelper do
       helper.push_frontend_feature_flag(:my_feature_flag, 10)
     end
   end
+
+  describe '#default_avatar_url' do
+    it 'returns an absolute URL' do
+      url = helper.default_avatar_url
+
+      expect(url).to match(/^http/)
+      expect(url).to match(/no_avatar.*png$/)
+    end
+  end
 end