Allow emoji in label and milestone references

If we put the emoji filter before the reference filters, each emoji will
have a wrapper element that prevents the reference filter from detecting
the presence of the emoji.

As the emoji filter now runs after the reference filters, references
must contain a literal emoji, not the GitLab Flavored Markdown
versions (:100`, for example).

A weird side-effect is that if you have a label with the 100 emoji, and
a label named 💯, then trying to reference the latter will work (link
to the correct label), but will render with the 100 emoji. I'm
comfortable with that edge case, I think.

changelogs/unreleased/allow-emoji-in-references.yml

+---
+title: Allow references to labels and milestones to contain emoji
+merge_request: 29284
+author:
+type: changed

lib/banzai/pipeline/gfm_pipeline.rb

@@ -25,7 +25,6 @@ module Banzai
           Filter::VideoLinkFilter,
           Filter::ImageLazyLoadFilter,
           Filter::ImageLinkFilter,
-          Filter::EmojiFilter,
           Filter::TableOfContentsFilter,
           Filter::AutolinkFilter,
           Filter::ExternalLinkFilter,
@@ -34,6 +33,7 @@ module Banzai
 
           *reference_filters,
 
+          Filter::EmojiFilter,
           Filter::TaskListFilter,
           Filter::InlineDiffFilter,
 

spec/lib/banzai/pipeline/gfm_pipeline_spec.rb

@@ -117,4 +117,27 @@ describe Banzai::Pipeline::GfmPipeline do
       expect(output).not_to include("javascript")
     end
   end
+
+  describe 'emoji in references' do
+    set(:project) { create(:project, :public) }
+    let(:emoji) { '💯' }
+
+    it 'renders a label reference with emoji inside' do
+      create(:label, project: project, name: emoji)
+
+      output = described_class.to_html("#{Label.reference_prefix}\"#{emoji}\"", project: project)
+
+      expect(output).to include(emoji)
+      expect(output).to include(Gitlab::Routing.url_helpers.project_issues_path(project, label_name: emoji))
+    end
+
+    it 'renders a milestone reference with emoji inside' do
+      milestone = create(:milestone, project: project, title: emoji)
+
+      output = described_class.to_html("#{Milestone.reference_prefix}\"#{emoji}\"", project: project)
+
+      expect(output).to include(emoji)
+      expect(output).to include(Gitlab::Routing.url_helpers.milestone_path(milestone))
+    end
+  end
 end