Fix first line markdown helper for user profile activity stream

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/29425

app/helpers/events_helper.rb

@@ -165,8 +165,8 @@ module EventsHelper
     sanitize(
       text,
-      tags: %w(a img b pre code p span),
-      attributes: Rails::Html::WhiteListSanitizer.allowed_attributes + ['style']
+      tags: %w(a img gl-emoji b pre code p span),
+      attributes: Rails::Html::WhiteListSanitizer.allowed_attributes + ['style', 'data-name', 'data-unicode-version', 'data-fallback-src', 'data-fallback-sprite-class']
     )
   end

app/helpers/gitlab_markdown_helper.rb

@@ -172,7 +172,7 @@ module GitlabMarkdownHelper
   # text hasn't already been truncated, then append "..." to the node contents
   # and return true.  Otherwise return false.
   def truncate_if_block(node, truncated)
-    if node.element? && node.description.block? && !truncated
+    if node.element? && node&.description&.block? && !truncated
       node.inner_html = "#{node.inner_html}..." if node.next_sibling
       true
     else

spec/helpers/gitlab_markdown_helper_spec.rb

@@ -152,9 +152,8 @@ describe GitlabMarkdownHelper do
   end
   describe '#first_line_in_markdown' do
-    let(:text) { "@#{user.username}, can you look at this?\nHello world\n"}
-
     it 'truncates Markdown properly' do
+      text = "@#{user.username}, can you look at this?\nHello world\n"
       actual = first_line_in_markdown(text, 100, project: project)
       doc = Nokogiri::HTML.parse(actual)
@@ -169,6 +168,23 @@ describe GitlabMarkdownHelper do
       expect(doc.content).to eq "@#{user.username}, can you look at this?..."
     end
+
+    it 'truncates Markdown with emoji properly' do
+      text = "foo :wink:\nbar :grinning:"
+      actual = first_line_in_markdown(text, 100, project: project)
+
+      doc = Nokogiri::HTML.parse(actual)
+
+      # Make sure we didn't create invalid markup
+      # But also account for the 2 errors caused by the unknown `gl-emoji` elements
+      expect(doc.errors.length).to eq(2)
+
+      expect(doc.css('gl-emoji').length).to eq(2)
+      expect(doc.css('gl-emoji')[0].attr('data-name')).to eq 'wink'
+      expect(doc.css('gl-emoji')[1].attr('data-name')).to eq 'grinning'
+
+      expect(doc.content).to eq "foo 😉\nbar 😀"
+    end
   end
   describe '#cross_project_reference' do