Post-process GFM after truncating the HTML

This is so that we only post-process the truncated
HTML and save some unnecessary Gitaly calls

app/helpers/markup_helper.rb

@@ -76,13 +76,14 @@ module MarkupHelper
   # +max_chars+ limit.  If the length limit falls within a tag's contents, then
   # the tag contents are truncated without removing the closing tag.
   def first_line_in_markdown(object, attribute, max_chars = nil, options = {})
-    md = markdown_field(object, attribute, options)
+    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 << 'img' if options[:allow_images]
 
     text = truncate_visible(md, max_chars || md.length)
+    text = prepare_for_rendering(text, markdown_field_render_context(object, attribute, options))
     text = sanitize(
       text,
       tags: tags,
@@ -107,15 +108,12 @@ module MarkupHelper
 
   def markdown_field(object, field, context = {})
     object = object.for_display if object.respond_to?(:for_display)
-    redacted_field_html = object.try(:"redacted_#{field}_html")
-
     return '' unless object.present?
-    return redacted_field_html if redacted_field_html
 
-    html = Banzai.render_field(object, field, context)
-    context.reverse_merge!(object.banzai_render_context(field)) if object.respond_to?(:banzai_render_context)
+    redacted_field_html = object.try(:"redacted_#{field}_html")
+    return redacted_field_html if redacted_field_html
 
-    prepare_for_rendering(html, context)
+    render_markdown_field(object, field, context)
   end
 
   def markup(file_name, text, context = {})
@@ -277,6 +275,23 @@ module MarkupHelper
     Gitlab::OtherMarkup.render(file_name, text, context)
   end
 
+  def render_markdown_field(object, field, context = {})
+    post_process = context.delete(:post_process)
+    post_process = true if post_process.nil?
+
+    html = Banzai.render_field(object, field, context)
+
+    return html unless post_process
+
+    prepare_for_rendering(html, markdown_field_render_context(object, field, context))
+  end
+
+  def markdown_field_render_context(object, field, base_context = {})
+    return base_context unless object.respond_to?(:banzai_render_context)
+
+    base_context.reverse_merge(object.banzai_render_context(field))
+  end
+
   def prepare_for_rendering(html, context = {})
     return '' unless html.present?
 

changelogs/unreleased/39509-todos-should-not-depend-on-gitaly-calls.yml

+---
+title: Prevent unnecessary Gitaly calls when rendering comment excerpts in todos and
+  activity feed
+merge_request: 23100
+author:
+type: performance

spec/helpers/markup_helper_spec.rb

@@ -138,10 +138,20 @@ describe MarkupHelper do
     describe 'without redacted attribute' do
       it 'renders the markdown value' do
         expect(Banzai).to receive(:render_field).with(commit, attribute, {}).and_call_original
+        expect(Banzai).to receive(:post_process)
 
         helper.markdown_field(commit, attribute)
       end
     end
+
+    context 'when post_process is false' do
+      it 'does not run Markdown post processing' do
+        expect(Banzai).to receive(:render_field).with(commit, attribute, {}).and_call_original
+        expect(Banzai).not_to receive(:post_process)
+
+        helper.markdown_field(commit, attribute, post_process: false)
+      end
+    end
   end
 
   describe '#link_to_markdown_field' do
@@ -565,6 +575,14 @@ describe MarkupHelper do
 
         expect(doc.content).to eq "foo 😉\nbar 😀"
       end
+
+      it 'does not post-process truncated text', :request_store do
+        object = create_object("hello \n\n [Test](README.md)")
+
+        expect do
+          first_line_in_markdown(object, attribute, nil, project: project)
+        end.not_to change { Gitlab::GitalyClient.get_request_count }
+      end
     end
 
     context 'when the asked attribute can be redacted' do