Remove Banzai::Renderer::CommonMark::HTML renderer

config/feature_flags/development/use_cmark_renderer.yml

+---
+name: use_cmark_renderer
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/61792
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/345744
+milestone: '14.6'
+type: development
+group: group::project management
+default_enabled: false

lib/banzai/filter/footnote_filter.rb

@@ -16,37 +16,60 @@ module Banzai
     # can be used for a single render). So you get `id=fn1-4335` and `id=fn2-4335`.
     #
     class FootnoteFilter < HTML::Pipeline::Filter
-      INTEGER_PATTERN                 = /\A\d+\z/.freeze
-      FOOTNOTE_ID_PREFIX              = 'fn'
-      FOOTNOTE_LINK_ID_PREFIX         = 'fnref'
-      FOOTNOTE_LI_REFERENCE_PATTERN   = /\A#{FOOTNOTE_ID_PREFIX}\d+\z/.freeze
-      FOOTNOTE_LINK_REFERENCE_PATTERN = /\A#{FOOTNOTE_LINK_ID_PREFIX}\d+\z/.freeze
-      FOOTNOTE_START_NUMBER           = 1
-
-      CSS_SECTION    = "ol > li[id=#{FOOTNOTE_ID_PREFIX}#{FOOTNOTE_START_NUMBER}]"
+      FOOTNOTE_ID_PREFIX              = 'fn-'
+      FOOTNOTE_LINK_ID_PREFIX         = 'fnref-'
+      FOOTNOTE_LI_REFERENCE_PATTERN   = /\A#{FOOTNOTE_ID_PREFIX}.+\z/.freeze
+      FOOTNOTE_LINK_REFERENCE_PATTERN = /\A#{FOOTNOTE_LINK_ID_PREFIX}.+\z/.freeze
+
+      CSS_SECTION    = "ol > li a[href^=\"\##{FOOTNOTE_LINK_ID_PREFIX}\"]"
       XPATH_SECTION  = Gitlab::Utils::Nokogiri.css_to_xpath(CSS_SECTION).freeze
       CSS_FOOTNOTE   = 'sup > a[id]'
       XPATH_FOOTNOTE = Gitlab::Utils::Nokogiri.css_to_xpath(CSS_FOOTNOTE).freeze
 
+      # only needed when feature flag use_cmark_renderer is turned off
+      INTEGER_PATTERN                     = /\A\d+\z/.freeze
+      FOOTNOTE_ID_PREFIX_OLD              = 'fn'
+      FOOTNOTE_LINK_ID_PREFIX_OLD         = 'fnref'
+      FOOTNOTE_LI_REFERENCE_PATTERN_OLD   = /\A#{FOOTNOTE_ID_PREFIX_OLD}\d+\z/.freeze
+      FOOTNOTE_LINK_REFERENCE_PATTERN_OLD = /\A#{FOOTNOTE_LINK_ID_PREFIX_OLD}\d+\z/.freeze
+      FOOTNOTE_START_NUMBER               = 1
+      CSS_SECTION_OLD                     = "ol > li[id=#{FOOTNOTE_ID_PREFIX_OLD}#{FOOTNOTE_START_NUMBER}]"
+      XPATH_SECTION_OLD                   = Gitlab::Utils::Nokogiri.css_to_xpath(CSS_SECTION_OLD).freeze
+
       def call
-        return doc unless first_footnote = doc.at_xpath(XPATH_SECTION)
+        xpath_section = Feature.enabled?(:use_cmark_renderer) ? XPATH_SECTION : XPATH_SECTION_OLD
+        return doc unless first_footnote = doc.at_xpath(xpath_section)
 
         # Sanitization stripped off the section wrapper - add it back in
-        first_footnote.parent.wrap('<section class="footnotes">')
+        if Feature.enabled?(:use_cmark_renderer)
+          first_footnote.parent.parent.parent.wrap('<section class="footnotes" data-footnotes>')
+        else
+          first_footnote.parent.wrap('<section class="footnotes">')
+        end
+
         rand_suffix = "-#{random_number}"
         modified_footnotes = {}
 
         doc.xpath(XPATH_FOOTNOTE).each do |link_node|
-          ref_num       = link_node[:id].delete_prefix(FOOTNOTE_LINK_ID_PREFIX)
-          node_xpath    = Gitlab::Utils::Nokogiri.css_to_xpath("li[id=#{fn_id(ref_num)}]")
+          if Feature.enabled?(:use_cmark_renderer)
+            ref_num = link_node[:id].delete_prefix(FOOTNOTE_LINK_ID_PREFIX)
+            ref_num.gsub!(/[[:punct:]]/, '\\\\\&')
+          else
+            ref_num = link_node[:id].delete_prefix(FOOTNOTE_LINK_ID_PREFIX_OLD)
+          end
+
+          node_xpath = Gitlab::Utils::Nokogiri.css_to_xpath("li[id=#{fn_id(ref_num)}]")
           footnote_node = doc.at_xpath(node_xpath)
 
-          if INTEGER_PATTERN.match?(ref_num) && (footnote_node || modified_footnotes[ref_num])
+          if footnote_node || modified_footnotes[ref_num]
+            next if Feature.disabled?(:use_cmark_renderer) && !INTEGER_PATTERN.match?(ref_num)
+
             link_node[:href] += rand_suffix
             link_node[:id]   += rand_suffix
 
             # Sanitization stripped off class - add it back in
             link_node.parent.append_class('footnote-ref')
+            link_node['data-footnote-ref'] = nil if Feature.enabled?(:use_cmark_renderer)
 
             unless modified_footnotes[ref_num]
               footnote_node[:id] += rand_suffix
@@ -55,6 +78,7 @@ module Banzai
               if backref_node
                 backref_node[:href] += rand_suffix
                 backref_node.append_class('footnote-backref')
+                backref_node['data-footnote-backref'] = nil if Feature.enabled?(:use_cmark_renderer)
               end
 
               modified_footnotes[ref_num] = true
@@ -72,11 +96,13 @@ module Banzai
       end
 
       def fn_id(num)
-        "#{FOOTNOTE_ID_PREFIX}#{num}"
+        prefix = Feature.enabled?(:use_cmark_renderer) ? FOOTNOTE_ID_PREFIX : FOOTNOTE_ID_PREFIX_OLD
+        "#{prefix}#{num}"
       end
 
       def fnref_id(num)
-        "#{FOOTNOTE_LINK_ID_PREFIX}#{num}"
+        prefix = Feature.enabled?(:use_cmark_renderer) ? FOOTNOTE_LINK_ID_PREFIX : FOOTNOTE_LINK_ID_PREFIX_OLD
+        "#{prefix}#{num}"
       end
     end
   end

lib/banzai/filter/markdown_engines/common_mark.rb

@@ -13,8 +13,7 @@ module Banzai
         EXTENSIONS = [
           :autolink,      # provides support for automatically converting URLs to anchor tags.
           :strikethrough, # provides support for strikethroughs.
-          :table,         # provides support for tables.
-          :tagfilter      # strips out several "unsafe" HTML tags from being used: https://github.github.com/gfm/#disallowed-raw-html-extension-
+          :table          # provides support for tables.
         ].freeze
 
         PARSE_OPTIONS = [
@@ -23,36 +22,63 @@ module Banzai
           :VALIDATE_UTF8               # replace illegal sequences with the replacement character U+FFFD.
         ].freeze
 
+        RENDER_OPTIONS_C = [
+          :GITHUB_PRE_LANG,  # use GitHub-style <pre lang> for fenced code blocks.
+          :FOOTNOTES,        # render footnotes.
+          :FULL_INFO_STRING, # include full info strings of code blocks in separate attribute.
+          :UNSAFE            # allow raw/custom HTML and unsafe links.
+        ].freeze
+
         # The `:GITHUB_PRE_LANG` option is not used intentionally because
         # it renders a fence block with language as `<pre lang="LANG"><code>some code\n</code></pre>`
         # while GitLab's syntax is `<pre><code lang="LANG">some code\n</code></pre>`.
         # If in the future the syntax is about to be made GitHub-compatible, please, add `:GITHUB_PRE_LANG` render option below
         # and remove `code_block` method from `lib/banzai/renderer/common_mark/html.rb`.
-        RENDER_OPTIONS = [
+        RENDER_OPTIONS_RUBY = [
           # as of commonmarker 0.18.0, we need to use :UNSAFE to get the same as the original :DEFAULT
           # https://github.com/gjtorikian/commonmarker/pull/81
-          :UNSAFE
-        ].freeze
-
-        RENDER_OPTIONS_SOURCEPOS = RENDER_OPTIONS + [
-          :SOURCEPOS # enable embedding of source position information
+          :UNSAFE # allow raw/custom HTML and unsafe links.
         ].freeze
 
         def initialize(context)
-          @context  = context
-          @renderer = Banzai::Renderer::CommonMark::HTML.new(options: render_options)
+          @context = context
+          @renderer = Banzai::Renderer::CommonMark::HTML.new(options: render_options) if Feature.disabled?(:use_cmark_renderer)
         end
 
         def render(text)
-          doc = CommonMarker.render_doc(text, PARSE_OPTIONS, EXTENSIONS)
+          if Feature.enabled?(:use_cmark_renderer)
+            CommonMarker.render_html(text, render_options, extensions)
+          else
+            doc = CommonMarker.render_doc(text, PARSE_OPTIONS, extensions)
 
-          @renderer.render(doc)
+            @renderer.render(doc)
+          end
         end
 
         private
 
+        def extensions
+          if Feature.enabled?(:use_cmark_renderer)
+            EXTENSIONS
+          else
+            EXTENSIONS + [
+              :tagfilter # strips out several "unsafe" HTML tags from being used: https://github.github.com/gfm/#disallowed-raw-html-extension-
+            ].freeze
+          end
+        end
+
         def render_options
-          @context[:no_sourcepos] ? RENDER_OPTIONS : RENDER_OPTIONS_SOURCEPOS
+          @context[:no_sourcepos] ? render_options_no_sourcepos : render_options_sourcepos
+        end
+
+        def render_options_no_sourcepos
+          Feature.enabled?(:use_cmark_renderer) ? RENDER_OPTIONS_C : RENDER_OPTIONS_RUBY
+        end
+
+        def render_options_sourcepos
+          render_options_no_sourcepos + [
+            :SOURCEPOS # enable embedding of source position information
+          ].freeze
         end
       end
     end

lib/banzai/filter/markdown_post_escape_filter.rb

@@ -8,10 +8,8 @@ module Banzai
       NOT_LITERAL_REGEX = %r{#{LITERAL_KEYWORD}-((%5C|\\).+?)-#{LITERAL_KEYWORD}}.freeze
       SPAN_REGEX        = %r{<span>(.*?)</span>}.freeze
 
-      CSS_A      = 'a'
-      XPATH_A    = Gitlab::Utils::Nokogiri.css_to_xpath(CSS_A).freeze
-      CSS_CODE   = 'code'
-      XPATH_CODE = Gitlab::Utils::Nokogiri.css_to_xpath(CSS_CODE).freeze
+      CSS_A   = 'a'
+      XPATH_A = Gitlab::Utils::Nokogiri.css_to_xpath(CSS_A).freeze
 
       def call
         return doc unless result[:escaped_literals]
@@ -34,12 +32,22 @@ module Banzai
           node.attributes['title'].value = node.attributes['title'].value.gsub(SPAN_REGEX, '\1') if node.attributes['title']
         end
 
-        doc.xpath(XPATH_CODE).each do |node|
+        doc.xpath(lang_tag).each do |node|
           node.attributes['lang'].value  = node.attributes['lang'].value.gsub(SPAN_REGEX, '\1') if node.attributes['lang']
         end
 
         doc
       end
+
+      private
+
+      def lang_tag
+        if Feature.enabled?(:use_cmark_renderer)
+          Gitlab::Utils::Nokogiri.css_to_xpath('pre')
+        else
+          Gitlab::Utils::Nokogiri.css_to_xpath('code')
+        end
+      end
     end
   end
 end

lib/banzai/filter/plantuml_filter.rb

@@ -5,18 +5,15 @@ require "asciidoctor_plantuml/plantuml"
 
 module Banzai
   module Filter
-    # HTML that replaces all `code plantuml` tags with PlantUML img tags.
+    # HTML that replaces all `lang plantuml` tags with PlantUML img tags.
     #
     class PlantumlFilter < HTML::Pipeline::Filter
-      CSS   = 'pre > code[lang="plantuml"]'
-      XPATH = Gitlab::Utils::Nokogiri.css_to_xpath(CSS).freeze
-
       def call
-        return doc unless settings.plantuml_enabled? && doc.at_xpath(XPATH)
+        return doc unless settings.plantuml_enabled? && doc.at_xpath(lang_tag)
 
         plantuml_setup
 
-        doc.xpath(XPATH).each do |node|
+        doc.xpath(lang_tag).each do |node|
           img_tag = Nokogiri::HTML::DocumentFragment.parse(
             Asciidoctor::PlantUml::Processor.plantuml_content(node.content, {}))
           node.parent.replace(img_tag)
@@ -27,6 +24,15 @@ module Banzai
 
       private
 
+      def lang_tag
+        @lang_tag ||=
+          if Feature.enabled?(:use_cmark_renderer)
+            Gitlab::Utils::Nokogiri.css_to_xpath('pre[lang="plantuml"] > code').freeze
+          else
+            Gitlab::Utils::Nokogiri.css_to_xpath('pre > code[lang="plantuml"]').freeze
+          end
+      end
+
       def settings
         Gitlab::CurrentSettings.current_application_settings
       end

lib/banzai/filter/sanitization_filter.rb

@@ -54,8 +54,13 @@ module Banzai
             return unless node.name == 'a' || node.name == 'li'
             return unless node.has_attribute?('id')
 
-            return if node.name == 'a' && node['id'] =~ Banzai::Filter::FootnoteFilter::FOOTNOTE_LINK_REFERENCE_PATTERN
-            return if node.name == 'li' && node['id'] =~ Banzai::Filter::FootnoteFilter::FOOTNOTE_LI_REFERENCE_PATTERN
+            if Feature.enabled?(:use_cmark_renderer)
+              return if node.name == 'a' && node['id'] =~ Banzai::Filter::FootnoteFilter::FOOTNOTE_LINK_REFERENCE_PATTERN
+              return if node.name == 'li' && node['id'] =~ Banzai::Filter::FootnoteFilter::FOOTNOTE_LI_REFERENCE_PATTERN
+            else
+              return if node.name == 'a' && node['id'] =~ Banzai::Filter::FootnoteFilter::FOOTNOTE_LINK_REFERENCE_PATTERN_OLD
+              return if node.name == 'li' && node['id'] =~ Banzai::Filter::FootnoteFilter::FOOTNOTE_LI_REFERENCE_PATTERN_OLD
+            end
 
             node.remove_attribute('id')
           end

lib/banzai/filter/syntax_highlight_filter.rb

@@ -11,7 +11,7 @@ module Banzai
     class SyntaxHighlightFilter < HTML::Pipeline::Filter
       include OutputSafety
 
-      PARAMS_DELIMITER = ':'
+      LANG_PARAMS_DELIMITER = ':'
       LANG_PARAMS_ATTR = 'data-lang-params'
 
       CSS   = 'pre:not([data-math-style]):not([data-mermaid-style]):not([data-kroki-style]) > code'
@@ -27,7 +27,7 @@ module Banzai
 
       def highlight_node(node)
         css_classes = +'code highlight js-syntax-highlight'
-        lang, lang_params = parse_lang_params(node.attr('lang'))
+        lang, lang_params = parse_lang_params(node)
         sourcepos = node.parent.attr('data-sourcepos')
         retried = false
 
@@ -56,7 +56,7 @@ module Banzai
           retry
         end
 
-        sourcepos_attr = sourcepos ? "data-sourcepos=\"#{sourcepos}\"" : ""
+        sourcepos_attr = sourcepos ? "data-sourcepos=\"#{sourcepos}\"" : ''
 
         highlighted = %(<pre #{sourcepos_attr} class="#{css_classes}"
                              lang="#{language}"
@@ -69,13 +69,36 @@ module Banzai
 
       private
 
-      def parse_lang_params(language)
+      def parse_lang_params(node)
+        node = node.parent if Feature.enabled?(:use_cmark_renderer)
+
+        # Commonmarker's FULL_INFO_STRING render option works with the space delimiter.
+        # But the current behavior of GitLab's markdown renderer is different - it grabs everything as the single
+        # line, including language and its options. To keep backward compatability, we have to parse the old format and
+        # merge with the new one.
+        #
+        # Behaviors before separating language and its parameters:
+        # Old ones:
+        # "```ruby with options```" -> '<pre><code lang="ruby with options">'.
+        # "```ruby:with:options```" -> '<pre><code lang="ruby:with:options">'.
+        #
+        # New ones:
+        # "```ruby with options```" -> '<pre><code lang="ruby" data-meta="with options">'.
+        # "```ruby:with:options```" -> '<pre><code lang="ruby:with:options">'.
+
+        language = node.attr('lang')
+
         return unless language
 
-        lang, params = language.split(PARAMS_DELIMITER, 2)
-        formatted_params = %(#{LANG_PARAMS_ATTR}="#{escape_once(params)}") if params
+        language, language_params = language.split(LANG_PARAMS_DELIMITER, 2)
+
+        if Feature.enabled?(:use_cmark_renderer)
+          language_params = [node.attr('data-meta'), language_params].compact.join(' ')
+        end
+
+        formatted_language_params = format_language_params(language_params)
 
-        [lang, formatted_params]
+        [language, formatted_language_params]
       end
 
       # Separate method so it can be instrumented.
@@ -95,6 +118,12 @@ module Banzai
       def use_rouge?(language)
         (%w(math suggestion) + ::AsciidoctorExtensions::Kroki::SUPPORTED_DIAGRAM_NAMES).exclude?(language)
       end
+
+      def format_language_params(language_params)
+        return if language_params.blank?
+
+        %(#{LANG_PARAMS_ATTR}="#{escape_once(language_params)}")
+      end
     end
   end
 end

lib/banzai/renderer/common_mark/html.rb

 # frozen_string_literal: true
 
+# Remove this entire file when removing `use_cmark_renderer` feature flag and switching to the CMARK html renderer.
+# https://gitlab.com/gitlab-org/gitlab/-/issues/345744
 module Banzai
   module Renderer
     module CommonMark

lib/gitlab/asciidoc/syntax_highlighter/html_pipeline_adapter.rb

@@ -7,7 +7,11 @@ module Gitlab
         register_for 'gitlab-html-pipeline'
 
         def format(node, lang, opts)
-          %(<pre><code #{lang ? %[ lang="#{lang}"] : ''}>#{node.content}</code></pre>)
+          if Feature.enabled?(:use_cmark_renderer)
+            %(<pre #{lang ? %[lang="#{lang}"] : ''}><code>#{node.content}</code></pre>)
+          else
+            %(<pre><code #{lang ? %[ lang="#{lang}"] : ''}>#{node.content}</code></pre>)
+          end
         end
       end
     end

spec/lib/banzai/filter/footnote_filter_spec.rb

@@ -5,34 +5,42 @@ require 'spec_helper'
 RSpec.describe Banzai::Filter::FootnoteFilter do
   include FilterSpecHelper
 
-  # first[^1] and second[^second]
+  # rubocop:disable Style/AsciiComments
+  # first[^1] and second[^second] and third[^_😄_]
   # [^1]: one
   # [^second]: two
+  # [^_😄_]: three
+  # rubocop:enable Style/AsciiComments
   let(:footnote) do
-    <<~EOF
-      <p>first<sup><a href="#fn1" id="fnref1">1</a></sup> and second<sup><a href="#fn2" id="fnref2">2</a></sup></p>
-      <p>same reference<sup><a href="#fn1" id="fnref1">1</a></sup></p>
+    <<~EOF.strip_heredoc
+      <p>first<sup><a href="#fn-1" id="fnref-1">1</a></sup> and second<sup><a href="#fn-second" id="fnref-second">2</a></sup> and third<sup><a href="#fn-_%F0%9F%98%84_" id="fnref-_%F0%9F%98%84_">3</a></sup></p>
+
       <ol>
-      <li id="fn1">
-      <p>one <a href="#fnref1">↩</a></p>
+      <li id="fn-1">
+      <p>one <a href="#fnref-1" aria-label="Back to content">↩</a></p>
       </li>
-      <li id="fn2">
-      <p>two <a href="#fnref2">↩</a></p>
+      <li id="fn-second">
+      <p>two <a href="#fnref-second" aria-label="Back to content">↩</a></p>
+      </li>\n<li id="fn-_%F0%9F%98%84_">
+      <p>three <a href="#fnref-_%F0%9F%98%84_" aria-label="Back to content">↩</a></p>
       </li>
       </ol>
     EOF
   end
 
   let(:filtered_footnote) do
-    <<~EOF
-      <p>first<sup class="footnote-ref"><a href="#fn1-#{identifier}" id="fnref1-#{identifier}">1</a></sup> and second<sup class="footnote-ref"><a href="#fn2-#{identifier}" id="fnref2-#{identifier}">2</a></sup></p>
-      <p>same reference<sup class="footnote-ref"><a href="#fn1-#{identifier}" id="fnref1-#{identifier}">1</a></sup></p>
-      <section class="footnotes"><ol>
-      <li id="fn1-#{identifier}">
-      <p>one <a href="#fnref1-#{identifier}" class="footnote-backref">↩</a></p>
+    <<~EOF.strip_heredoc
+      <p>first<sup class="footnote-ref"><a href="#fn-1-#{identifier}" id="fnref-1-#{identifier}" data-footnote-ref="">1</a></sup> and second<sup class="footnote-ref"><a href="#fn-second-#{identifier}" id="fnref-second-#{identifier}" data-footnote-ref="">2</a></sup> and third<sup class="footnote-ref"><a href="#fn-_%F0%9F%98%84_-#{identifier}" id="fnref-_%F0%9F%98%84_-#{identifier}" data-footnote-ref="">3</a></sup></p>
+
+      <section class=\"footnotes\" data-footnotes><ol>
+      <li id="fn-1-#{identifier}">
+      <p>one <a href="#fnref-1-#{identifier}" aria-label="Back to content" class="footnote-backref" data-footnote-backref="">↩</a></p>
+      </li>
+      <li id="fn-second-#{identifier}">
+      <p>two <a href="#fnref-second-#{identifier}" aria-label="Back to content" class="footnote-backref" data-footnote-backref="">↩</a></p>
       </li>
-      <li id="fn2-#{identifier}">
-      <p>two <a href="#fnref2-#{identifier}" class="footnote-backref">↩</a></p>
+      <li id="fn-_%F0%9F%98%84_-#{identifier}">
+      <p>three <a href="#fnref-_%F0%9F%98%84_-#{identifier}" aria-label="Back to content" class="footnote-backref" data-footnote-backref="">↩</a></p>
       </li>
       </ol></section>
     EOF
@@ -41,10 +49,56 @@ RSpec.describe Banzai::Filter::FootnoteFilter do
   context 'when footnotes exist' do
     let(:doc)        { filter(footnote) }
     let(:link_node)  { doc.css('sup > a').first }
-    let(:identifier) { link_node[:id].delete_prefix('fnref1-') }
+    let(:identifier) { link_node[:id].delete_prefix('fnref-1-') }
 
     it 'properly adds the necessary ids and classes' do
       expect(doc.to_html).to eq filtered_footnote
     end
+
+    context 'using ruby-based HTML renderer' do
+      # first[^1] and second[^second]
+      # [^1]: one
+      # [^second]: two
+      let(:footnote) do
+        <<~EOF
+          <p>first<sup><a href="#fn1" id="fnref1">1</a></sup> and second<sup><a href="#fn2" id="fnref2">2</a></sup></p>
+          <p>same reference<sup><a href="#fn1" id="fnref1">1</a></sup></p>
+          <ol>
+          <li id="fn1">
+          <p>one <a href="#fnref1">↩</a></p>
+          </li>
+          <li id="fn2">
+          <p>two <a href="#fnref2">↩</a></p>
+          </li>
+          </ol>
+        EOF
+      end
+
+      let(:filtered_footnote) do
+        <<~EOF
+          <p>first<sup class="footnote-ref"><a href="#fn1-#{identifier}" id="fnref1-#{identifier}">1</a></sup> and second<sup class="footnote-ref"><a href="#fn2-#{identifier}" id="fnref2-#{identifier}">2</a></sup></p>
+          <p>same reference<sup class="footnote-ref"><a href="#fn1-#{identifier}" id="fnref1-#{identifier}">1</a></sup></p>
+          <section class="footnotes"><ol>
+          <li id="fn1-#{identifier}">
+          <p>one <a href="#fnref1-#{identifier}" class="footnote-backref">↩</a></p>
+          </li>
+          <li id="fn2-#{identifier}">
+          <p>two <a href="#fnref2-#{identifier}" class="footnote-backref">↩</a></p>
+          </li>
+          </ol></section>
+        EOF
+      end
+
+      let(:doc)        { filter(footnote) }
+      let(:identifier) { link_node[:id].delete_prefix('fnref1-') }
+
+      before do
+        stub_feature_flags(use_cmark_renderer: false)
+      end
+
+      it 'properly adds the necessary ids and classes' do
+        expect(doc.to_html).to eq filtered_footnote
+      end
+    end
   end
 end

spec/lib/banzai/filter/markdown_filter_spec.rb

@@ -5,90 +5,125 @@ require 'spec_helper'
 RSpec.describe Banzai::Filter::MarkdownFilter do
   include FilterSpecHelper
 
-  describe 'markdown engine from context' do
-    it 'defaults to CommonMark' do
-      expect_next_instance_of(Banzai::Filter::MarkdownEngines::CommonMark) do |instance|
-        expect(instance).to receive(:render).and_return('test')
+  shared_examples_for 'renders correct markdown' do
+    describe 'markdown engine from context' do
+      it 'defaults to CommonMark' do
+        expect_next_instance_of(Banzai::Filter::MarkdownEngines::CommonMark) do |instance|
+          expect(instance).to receive(:render).and_return('test')
+        end
+
+        filter('test')
       end
 
-      filter('test')
-    end
+      it 'uses CommonMark' do
+        expect_next_instance_of(Banzai::Filter::MarkdownEngines::CommonMark) do |instance|
+          expect(instance).to receive(:render).and_return('test')
+        end
 
-    it 'uses CommonMark' do
-      expect_next_instance_of(Banzai::Filter::MarkdownEngines::CommonMark) do |instance|
-        expect(instance).to receive(:render).and_return('test')
+        filter('test', { markdown_engine: :common_mark })
       end
-
-      filter('test', { markdown_engine: :common_mark })
     end
-  end
 
-  describe 'code block' do
-    context 'using CommonMark' do
-      before do
-        stub_const('Banzai::Filter::MarkdownFilter::DEFAULT_ENGINE', :common_mark)
+    describe 'code block' do
+      context 'using CommonMark' do
+        before do
+          stub_const('Banzai::Filter::MarkdownFilter::DEFAULT_ENGINE', :common_mark)
+        end
+
+        it 'adds language to lang attribute when specified' do
+          result = filter("```html\nsome code\n```", no_sourcepos: true)
+
+          if Feature.enabled?(:use_cmark_renderer)
+            expect(result).to start_with('<pre lang="html"><code>')
+          else
+            expect(result).to start_with('<pre><code lang="html">')
+          end
+        end
+
+        it 'does not add language to lang attribute when not specified' do
+          result = filter("```\nsome code\n```", no_sourcepos: true)
+
+          expect(result).to start_with('<pre><code>')
+        end
+
+        it 'works with utf8 chars in language' do
+          result = filter("```日\nsome code\n```", no_sourcepos: true)
+
+          if Feature.enabled?(:use_cmark_renderer)
+            expect(result).to start_with('<pre lang="日"><code>')
+          else
+            expect(result).to start_with('<pre><code lang="日">')
+          end
+        end
+
+        it 'works with additional language parameters' do
+          result = filter("```ruby:red gem foo\nsome code\n```", no_sourcepos: true)
+
+          if Feature.enabled?(:use_cmark_renderer)
+            expect(result).to start_with('<pre lang="ruby:red" data-meta="gem foo"><code>')
+          else
+            expect(result).to start_with('<pre><code lang="ruby:red gem foo">')
+          end
+        end
       end
+    end
 
-      it 'adds language to lang attribute when specified' do
-        result = filter("```html\nsome code\n```", no_sourcepos: true)
-
-        expect(result).to start_with('<pre><code lang="html">')
-      end
-
-      it 'does not add language to lang attribute when not specified' do
-        result = filter("```\nsome code\n```", no_sourcepos: true)
-
-        expect(result).to start_with('<pre><code>')
-      end
+    describe 'source line position' do
+      context 'using CommonMark' do
+        before do
+          stub_const('Banzai::Filter::MarkdownFilter::DEFAULT_ENGINE', :common_mark)
+        end
 
-      it 'works with utf8 chars in language' do
-        result = filter("```日\nsome code\n```", no_sourcepos: true)
+        it 'defaults to add data-sourcepos' do
+          result = filter('test')
 
-        expect(result).to start_with('<pre><code lang="日">')
-      end
+          expect(result).to eq '<p data-sourcepos="1:1-1:4">test</p>'
+        end
 
-      it 'works with additional language parameters' do
-        result = filter("```ruby:red gem\nsome code\n```", no_sourcepos: true)
+        it 'disables data-sourcepos' do
+          result = filter('test', no_sourcepos: true)
 
-        expect(result).to start_with('<pre><code lang="ruby:red gem">')
+          expect(result).to eq '<p>test</p>'
+        end
       end
     end
-  end
 
-  describe 'source line position' do
-    context 'using CommonMark' do
-      before do
-        stub_const('Banzai::Filter::MarkdownFilter::DEFAULT_ENGINE', :common_mark)
-      end
+    describe 'footnotes in tables' do
+      it 'processes footnotes in table cells' do
+        text = <<-MD.strip_heredoc
+      | Column1   |
+      | --------- |
+      | foot [^1] |
 
-      it 'defaults to add data-sourcepos' do
-        result = filter('test')
+      [^1]: a footnote
+        MD
 
-        expect(result).to eq '<p data-sourcepos="1:1-1:4">test</p>'
-      end
+        result = filter(text, no_sourcepos: true)
 
-      it 'disables data-sourcepos' do
-        result = filter('test', no_sourcepos: true)
+        expect(result).to include('<td>foot <sup')
 
-        expect(result).to eq '<p>test</p>'
+        if Feature.enabled?(:use_cmark_renderer)
+          expect(result).to include('<section class="footnotes" data-footnotes>')
+        else
+          expect(result).to include('<section class="footnotes">')
+        end
       end
     end
   end
 
-  describe 'footnotes in tables' do
-    it 'processes footnotes in table cells' do
-      text = <<-MD.strip_heredoc
-      | Column1   |
-      | --------- |
-      | foot [^1] |
-
-      [^1]: a footnote
-      MD
+  context 'using ruby-based HTML renderer' do
+    before do
+      stub_feature_flags(use_cmark_renderer: false)
+    end
 
-      result = filter(text, no_sourcepos: true)
+    it_behaves_like 'renders correct markdown'
+  end
 
-      expect(result).to include('<td>foot <sup')
-      expect(result).to include('<section class="footnotes">')
+  context 'using c-based HTML renderer' do
+    before do
+      stub_feature_flags(use_cmark_renderer: true)
     end
+
+    it_behaves_like 'renders correct markdown'
   end
 end

spec/lib/banzai/filter/plantuml_filter_spec.rb

@@ -5,30 +5,67 @@ require 'spec_helper'
 RSpec.describe Banzai::Filter::PlantumlFilter do
   include FilterSpecHelper
 
-  it 'replaces plantuml pre tag with img tag' do
-    stub_application_setting(plantuml_enabled: true, plantuml_url: "http://localhost:8080")
-    input = '<pre><code lang="plantuml">Bob -> Sara : Hello</code></pre>'
-    output = '<div class="imageblock"><div class="content"><img class="plantuml" src="http://localhost:8080/png/U9npoazIqBLJ24uiIbImKl18pSd91m0rkGMq"></div></div>'
-    doc = filter(input)
+  shared_examples_for 'renders correct markdown' do
+    it 'replaces plantuml pre tag with img tag' do
+      stub_application_setting(plantuml_enabled: true, plantuml_url: "http://localhost:8080")
 
-    expect(doc.to_s).to eq output
+      input = if Feature.enabled?(:use_cmark_renderer)
+                '<pre lang="plantuml"><code>Bob -> Sara : Hello</code></pre>'
+              else
+                '<pre><code lang="plantuml">Bob -> Sara : Hello</code></pre>'
+              end
+
+      output = '<div class="imageblock"><div class="content"><img class="plantuml" src="http://localhost:8080/png/U9npoazIqBLJ24uiIbImKl18pSd91m0rkGMq"></div></div>'
+      doc = filter(input)
+
+      expect(doc.to_s).to eq output
+    end
+
+    it 'does not replace plantuml pre tag with img tag if disabled' do
+      stub_application_setting(plantuml_enabled: false)
+
+      if Feature.enabled?(:use_cmark_renderer)
+        input = '<pre lang="plantuml"><code>Bob -> Sara : Hello</code></pre>'
+        output = '<pre lang="plantuml"><code>Bob -&gt; Sara : Hello</code></pre>'
+      else
+        input = '<pre><code lang="plantuml">Bob -> Sara : Hello</code></pre>'
+        output = '<pre><code lang="plantuml">Bob -&gt; Sara : Hello</code></pre>'
+      end
+
+      doc = filter(input)
+
+      expect(doc.to_s).to eq output
+    end
+
+    it 'does not replace plantuml pre tag with img tag if url is invalid' do
+      stub_application_setting(plantuml_enabled: true, plantuml_url: "invalid")
+
+      input = if Feature.enabled?(:use_cmark_renderer)
+                '<pre lang="plantuml"><code>Bob -> Sara : Hello</code></pre>'
+              else
+                '<pre><code lang="plantuml">Bob -> Sara : Hello</code></pre>'
+              end
+
+      output = '<div class="listingblock"><div class="content"><pre class="plantuml plantuml-error"> Error: cannot connect to PlantUML server at "invalid"</pre></div></div>'
+      doc = filter(input)
+
+      expect(doc.to_s).to eq output
+    end
   end
 
-  it 'does not replace plantuml pre tag with img tag if disabled' do
-    stub_application_setting(plantuml_enabled: false)
-    input = '<pre><code lang="plantuml">Bob -> Sara : Hello</code></pre>'
-    output = '<pre><code lang="plantuml">Bob -&gt; Sara : Hello</code></pre>'
-    doc = filter(input)
+  context 'using ruby-based HTML renderer' do
+    before do
+      stub_feature_flags(use_cmark_renderer: false)
+    end
 
-    expect(doc.to_s).to eq output
+    it_behaves_like 'renders correct markdown'
   end
 
-  it 'does not replace plantuml pre tag with img tag if url is invalid' do
-    stub_application_setting(plantuml_enabled: true, plantuml_url: "invalid")
-    input = '<pre><code lang="plantuml">Bob -> Sara : Hello</code></pre>'
-    output = '<div class="listingblock"><div class="content"><pre class="plantuml plantuml-error"> Error: cannot connect to PlantUML server at "invalid"</pre></div></div>'
-    doc = filter(input)
+  context 'using c-based HTML renderer' do
+    before do
+      stub_feature_flags(use_cmark_renderer: true)
+    end
 
-    expect(doc.to_s).to eq output
+    it_behaves_like 'renders correct markdown'
   end
 end

spec/lib/banzai/filter/sanitization_filter_spec.rb

@@ -45,10 +45,10 @@ RSpec.describe Banzai::Filter::SanitizationFilter do
 
     it 'allows `text-align` property in `style` attribute on table elements' do
       html = <<~HTML
-      <table>
-        <tr><th style="text-align: center">Head</th></tr>
-        <tr><td style="text-align: right">Body</th></tr>
-      </table>
+        <table>
+          <tr><th style="text-align: center">Head</th></tr>
+          <tr><td style="text-align: right">Body</th></tr>
+        </table>
       HTML
 
       doc = filter(html)
@@ -140,14 +140,14 @@ RSpec.describe Banzai::Filter::SanitizationFilter do
 
     describe 'footnotes' do
       it 'allows correct footnote id property on links' do
-        exp = %q(<a href="#fn1" id="fnref1">foo/bar.md</a>)
+        exp = %q(<a href="#fn-first" id="fnref-first">foo/bar.md</a>)
         act = filter(exp)
 
         expect(act.to_html).to eq exp
       end
 
       it 'allows correct footnote id property on li element' do
-        exp = %q(<ol><li id="fn1">footnote</li></ol>)
+        exp = %q(<ol><li id="fn-last">footnote</li></ol>)
         act = filter(exp)
 
         expect(act.to_html).to eq exp
@@ -156,7 +156,7 @@ RSpec.describe Banzai::Filter::SanitizationFilter do
       it 'removes invalid id for footnote links' do
         exp = %q(<a href="#fn1">link</a>)
 
-        %w[fnrefx test xfnref1].each do |id|
+        %w[fnrefx test xfnref-1].each do |id|
           act = filter(%(<a href="#fn1" id="#{id}">link</a>))
 
           expect(act.to_html).to eq exp
@@ -166,18 +166,58 @@ RSpec.describe Banzai::Filter::SanitizationFilter do
       it 'removes invalid id for footnote li' do
         exp = %q(<ol><li>footnote</li></ol>)
 
-        %w[fnx test xfn1].each do |id|
+        %w[fnx test xfn-1].each do |id|
           act = filter(%(<ol><li id="#{id}">footnote</li></ol>))
 
           expect(act.to_html).to eq exp
         end
       end
 
-      it 'allows footnotes numbered higher than 9' do
-        exp = %q(<a href="#fn15" id="fnref15">link</a><ol><li id="fn15">footnote</li></ol>)
-        act = filter(exp)
+      context 'using ruby-based HTML renderer' do
+        before do
+          stub_feature_flags(use_cmark_renderer: false)
+        end
 
-        expect(act.to_html).to eq exp
+        it 'allows correct footnote id property on links' do
+          exp = %q(<a href="#fn1" id="fnref1">foo/bar.md</a>)
+          act = filter(exp)
+
+          expect(act.to_html).to eq exp
+        end
+
+        it 'allows correct footnote id property on li element' do
+          exp = %q(<ol><li id="fn1">footnote</li></ol>)
+          act = filter(exp)
+
+          expect(act.to_html).to eq exp
+        end
+
+        it 'removes invalid id for footnote links' do
+          exp = %q(<a href="#fn1">link</a>)
+
+          %w[fnrefx test xfnref1].each do |id|
+            act = filter(%(<a href="#fn1" id="#{id}">link</a>))
+
+            expect(act.to_html).to eq exp
+          end
+        end
+
+        it 'removes invalid id for footnote li' do
+          exp = %q(<ol><li>footnote</li></ol>)
+
+          %w[fnx test xfn1].each do |id|
+            act = filter(%(<ol><li id="#{id}">footnote</li></ol>))
+
+            expect(act.to_html).to eq exp
+          end
+        end
+
+        it 'allows footnotes numbered higher than 9' do
+          exp = %q(<a href="#fn15" id="fnref15">link</a><ol><li id="fn15">footnote</li></ol>)
+          act = filter(exp)
+
+          expect(act.to_html).to eq exp
+        end
       end
     end
   end

spec/lib/banzai/pipeline/full_pipeline_spec.rb

@@ -31,29 +31,29 @@ RSpec.describe Banzai::Pipeline::FullPipeline do
   describe 'footnotes' do
     let(:project)    { create(:project, :public) }
     let(:html)       { described_class.to_html(footnote_markdown, project: project) }
-    let(:identifier) { html[/.*fnref1-(\d+).*/, 1] }
+    let(:identifier) { html[/.*fnref-1-(\d+).*/, 1] }
     let(:footnote_markdown) do
       <<~EOF
-        first[^1] and second[^second] and twenty[^twenty]
+        first[^1] and second[^😄second] and twenty[^_twenty]
         [^1]: one
-        [^second]: two
-        [^twenty]: twenty
+        [^😄second]: two
+        [^_twenty]: twenty
       EOF
     end
 
     let(:filtered_footnote) do
-      <<~EOF
-        <p dir="auto">first<sup class="footnote-ref"><a href="#fn1-#{identifier}" id="fnref1-#{identifier}">1</a></sup> and second<sup class="footnote-ref"><a href="#fn2-#{identifier}" id="fnref2-#{identifier}">2</a></sup> and twenty<sup class="footnote-ref"><a href="#fn3-#{identifier}" id="fnref3-#{identifier}">3</a></sup></p>
+      <<~EOF.strip_heredoc
+        <p dir="auto">first<sup class="footnote-ref"><a href="#fn-1-#{identifier}" id="fnref-1-#{identifier}" data-footnote-ref="">1</a></sup> and second<sup class="footnote-ref"><a href="#fn-%F0%9F%98%84second-#{identifier}" id="fnref-%F0%9F%98%84second-#{identifier}" data-footnote-ref="">2</a></sup> and twenty<sup class="footnote-ref"><a href="#fn-_twenty-#{identifier}" id="fnref-_twenty-#{identifier}" data-footnote-ref="">3</a></sup></p>
 
-        <section class="footnotes"><ol>
-        <li id="fn1-#{identifier}">
-        <p>one <a href="#fnref1-#{identifier}" class="footnote-backref"><gl-emoji title="leftwards arrow with hook" data-name="leftwards_arrow_with_hook" data-unicode-version="1.1">↩</gl-emoji></a></p>
+        <section class="footnotes" data-footnotes><ol>
+        <li id="fn-1-#{identifier}">
+        <p>one <a href="#fnref-1-#{identifier}" aria-label="Back to content" class="footnote-backref" data-footnote-backref=""><gl-emoji title="leftwards arrow with hook" data-name="leftwards_arrow_with_hook" data-unicode-version="1.1">↩</gl-emoji></a></p>
         </li>
-        <li id="fn2-#{identifier}">
-        <p>two <a href="#fnref2-#{identifier}" class="footnote-backref"><gl-emoji title="leftwards arrow with hook" data-name="leftwards_arrow_with_hook" data-unicode-version="1.1">↩</gl-emoji></a></p>
+        <li id="fn-%F0%9F%98%84second-#{identifier}">
+        <p>two <a href="#fnref-%F0%9F%98%84second-#{identifier}" aria-label="Back to content" class="footnote-backref" data-footnote-backref=""><gl-emoji title="leftwards arrow with hook" data-name="leftwards_arrow_with_hook" data-unicode-version="1.1">↩</gl-emoji></a></p>
         </li>
-        <li id="fn3-#{identifier}">
-        <p>twenty <a href="#fnref3-#{identifier}" class="footnote-backref"><gl-emoji title="leftwards arrow with hook" data-name="leftwards_arrow_with_hook" data-unicode-version="1.1">↩</gl-emoji></a></p>
+        <li id="fn-_twenty-#{identifier}">
+        <p>twenty <a href="#fnref-_twenty-#{identifier}" aria-label="Back to content" class="footnote-backref" data-footnote-backref=""><gl-emoji title="leftwards arrow with hook" data-name="leftwards_arrow_with_hook" data-unicode-version="1.1">↩</gl-emoji></a></p>
         </li>
         </ol></section>
       EOF
@@ -64,6 +64,47 @@ RSpec.describe Banzai::Pipeline::FullPipeline do
 
       expect(html.lines.map(&:strip).join("\n")).to eq filtered_footnote
     end
+
+    context 'using ruby-based HTML renderer' do
+      let(:html)       { described_class.to_html(footnote_markdown, project: project) }
+      let(:identifier) { html[/.*fnref1-(\d+).*/, 1] }
+      let(:footnote_markdown) do
+        <<~EOF
+          first[^1] and second[^second] and twenty[^twenty]
+          [^1]: one
+          [^second]: two
+          [^twenty]: twenty
+        EOF
+      end
+
+      let(:filtered_footnote) do
+        <<~EOF
+          <p dir="auto">first<sup class="footnote-ref"><a href="#fn1-#{identifier}" id="fnref1-#{identifier}">1</a></sup> and second<sup class="footnote-ref"><a href="#fn2-#{identifier}" id="fnref2-#{identifier}">2</a></sup> and twenty<sup class="footnote-ref"><a href="#fn3-#{identifier}" id="fnref3-#{identifier}">3</a></sup></p>
+
+          <section class="footnotes"><ol>
+          <li id="fn1-#{identifier}">
+          <p>one <a href="#fnref1-#{identifier}" class="footnote-backref"><gl-emoji title="leftwards arrow with hook" data-name="leftwards_arrow_with_hook" data-unicode-version="1.1">↩</gl-emoji></a></p>
+          </li>
+          <li id="fn2-#{identifier}">
+          <p>two <a href="#fnref2-#{identifier}" class="footnote-backref"><gl-emoji title="leftwards arrow with hook" data-name="leftwards_arrow_with_hook" data-unicode-version="1.1">↩</gl-emoji></a></p>
+          </li>
+          <li id="fn3-#{identifier}">
+          <p>twenty <a href="#fnref3-#{identifier}" class="footnote-backref"><gl-emoji title="leftwards arrow with hook" data-name="leftwards_arrow_with_hook" data-unicode-version="1.1">↩</gl-emoji></a></p>
+          </li>
+          </ol></section>
+        EOF
+      end
+
+      before do
+        stub_feature_flags(use_cmark_renderer: false)
+      end
+
+      it 'properly adds the necessary ids and classes' do
+        stub_commonmark_sourcepos_disabled
+
+        expect(html.lines.map(&:strip).join("\n")).to eq filtered_footnote
+      end
+    end
   end
 
   describe 'links are detected as malicious' do

spec/lib/banzai/pipeline/plain_markdown_pipeline_spec.rb

@@ -5,18 +5,7 @@ require 'spec_helper'
 RSpec.describe Banzai::Pipeline::PlainMarkdownPipeline do
   using RSpec::Parameterized::TableSyntax
 
-  describe 'backslash escapes' do
-    let_it_be(:project) { create(:project, :public) }
-    let_it_be(:issue)   { create(:issue, project: project) }
-
-    def correct_html_included(markdown, expected)
-      result = described_class.call(markdown, {})
-
-      expect(result[:output].to_html).to include(expected)
-
-      result
-    end
-
+  shared_examples_for 'renders correct markdown' do
     describe 'CommonMark tests', :aggregate_failures do
       it 'converts all reference punctuation to literals' do
         reference_chars = Banzai::Filter::MarkdownPreEscapeFilter::REFERENCE_CHARACTERS
@@ -79,10 +68,19 @@ RSpec.describe Banzai::Pipeline::PlainMarkdownPipeline do
       end
 
       describe 'work in all other contexts, including URLs and link titles, link references, and info strings in fenced code blocks' do
+        let(:markdown) { %Q(``` foo\\@bar\nfoo\n```) }
+
+        it 'renders correct html' do
+          if Feature.enabled?(:use_cmark_renderer)
+            correct_html_included(markdown, %Q(<pre data-sourcepos="1:1-3:3" lang="foo@bar"><code>foo\n</code></pre>))
+          else
+            correct_html_included(markdown, %Q(<code lang="foo@bar">foo\n</code>))
+          end
+        end
+
         where(:markdown, :expected) do
           %q![foo](/bar\@ "\@title")!            | %q(<a href="/bar@" title="@title">foo</a>)
           %Q![foo]\n\n[foo]: /bar\\@ "\\@title"! | %q(<a href="/bar@" title="@title">foo</a>)
-          %Q(``` foo\\@bar\nfoo\n```)            | %Q(<code lang="foo@bar">foo\n</code>)
         end
 
         with_them do
@@ -91,4 +89,33 @@ RSpec.describe Banzai::Pipeline::PlainMarkdownPipeline do
       end
     end
   end
+
+  describe 'backslash escapes' do
+    let_it_be(:project) { create(:project, :public) }
+    let_it_be(:issue)   { create(:issue, project: project) }
+
+    def correct_html_included(markdown, expected)
+      result = described_class.call(markdown, {})
+
+      expect(result[:output].to_html).to include(expected)
+
+      result
+    end
+
+    context 'using ruby-based HTML renderer' do
+      before do
+        stub_feature_flags(use_cmark_renderer: false)
+      end
+
+      it_behaves_like 'renders correct markdown'
+    end
+
+    context 'using c-based HTML renderer' do
+      before do
+        stub_feature_flags(use_cmark_renderer: true)
+      end
+
+      it_behaves_like 'renders correct markdown'
+    end
+  end
 end

spec/support/helpers/stub_gitlab_calls.rb

@@ -92,9 +92,16 @@ module StubGitlabCalls
   end
 
   def stub_commonmark_sourcepos_disabled
+    render_options =
+      if Feature.enabled?(:use_cmark_renderer)
+        Banzai::Filter::MarkdownEngines::CommonMark::RENDER_OPTIONS_C
+      else
+        Banzai::Filter::MarkdownEngines::CommonMark::RENDER_OPTIONS_RUBY
+      end
+
     allow_any_instance_of(Banzai::Filter::MarkdownEngines::CommonMark)
       .to receive(:render_options)
-      .and_return(Banzai::Filter::MarkdownEngines::CommonMark::RENDER_OPTIONS)
+      .and_return(render_options)
   end
 
   private