Fix rendering of scoped labels in todos

Add data-html and <i> to whitelist in first_line_in_markdown.
We need this tag and attribute to properly render scoped labels.

app/helpers/markup_helper.rb

@@ -79,7 +79,7 @@ module MarkupHelper
     md = markdown_field(object, attribute, options.merge(post_process: false))
     return unless md.present?
 
-    tags = %w(a gl-emoji b pre code p span)
+    tags = %w(a gl-emoji b strong i em pre code p span)
     tags << 'img' if options[:allow_images]
 
     text = truncate_visible(md, max_chars || md.length)
@@ -88,7 +88,7 @@ module MarkupHelper
       text,
       tags: tags,
       attributes: Rails::Html::WhiteListSanitizer.allowed_attributes +
-          %w(style data-src data-name data-unicode-version data-iid data-project-path data-mr-title)
+          %w(style data-src data-name data-unicode-version data-iid data-project-path data-mr-title data-html)
     )
 
     # since <img> tags are stripped, this can leave empty <a> tags hanging around
@@ -233,7 +233,7 @@ module MarkupHelper
 
   def strip_empty_link_tags(text)
     scrubber = Loofah::Scrubber.new do |node|
-      node.remove if node.name == 'a' && node.content.blank?
+      node.remove if node.name == 'a' && node.children.empty?
     end
 
     sanitize text, scrubber: scrubber

changelogs/unreleased/207462-scoped-labels-rendering-is-broken-in-todos.yml

+---
+title: Fix scoped labels rendering in To-Do List
+merge_request: 26146
+author:
+type: fixed

ee/spec/helpers/markup_helper_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe MarkupHelper do
+  let(:project) { create(:project, :public) }
+
+  describe '#first_line_in_markdown' do
+    context 'with scoped label references' do
+      let(:label) { create(:label, title: 'key::some name', project: project) }
+
+      before do
+        stub_licensed_features(scoped_labels: true)
+      end
+
+      it 'shows proper tooltip and documentation link' do
+        note = build(:note, note: label.to_reference, project: project)
+
+        result = first_line_in_markdown(note, :note, nil, project: project)
+        doc = Nokogiri::HTML.parse(result)
+
+        expect(doc.css('.gl-label-link')[0].attr('data-html')).to eq('true')
+        expect(doc.css('a .fa-question-circle').length).to eq(1)
+      end
+    end
+  end
+end

spec/helpers/markup_helper_spec.rb

@@ -531,8 +531,10 @@ describe MarkupHelper do
 
         it 'preserves style attribute for a label that can be accessed by current_user' do
           project = create(:project, :public)
+          label = create_and_format_label(project)
 
-          expect(create_and_format_label(project)).to match(/span class=.*style=.*/)
+          expect(label).to match(/span class=.*style=.*/)
+          expect(label).to include('data-html="true"')
         end
 
         it 'does not style a label that can not be accessed by current_user' do
@@ -544,6 +546,15 @@ describe MarkupHelper do
         end
       end
 
+      it 'keeps whitelisted tags' do
+        html = '<a><i></i></a> <strong>strong</strong><em>em</em><b>b</b>'
+
+        object = create_object(html)
+        result = first_line_in_markdown(object, attribute, 100, project: project)
+
+        expect(result).to include(html)
+      end
+
       it 'truncates Markdown properly' do
         object = create_object("@#{user.username}, can you look at this?\nHello world\n")
         actual = first_line_in_markdown(object, attribute, 100, project: project)