Add rel="nofollow" to links in comments (#3304)

* Add rel="nofollow" to links in comments

* Improve code quality and Add tests

app/labor/markdown_parser.rb

@@ -6,8 +6,9 @@ class MarkdownParser
     @content = content
   end
 
-  def finalize
-    renderer = Redcarpet::Render::HTMLRouge.new(hard_wrap: true, filter_html: false)
+  def finalize(link_attributes: {})
+    options = { hard_wrap: true, filter_html: false, link_attributes: link_attributes }
+    renderer = Redcarpet::Render::HTMLRouge.new(options)
     markdown = Redcarpet::Markdown.new(renderer, REDCARPET_CONFIG)
     catch_xss_attempts(@content)
     escaped_content = escape_liquid_tags_in_codeblock(@content)

app/models/comment.rb

@@ -213,7 +213,7 @@ class Comment < ApplicationRecord
   def evaluate_markdown
     fixed_body_markdown = MarkdownFixer.fix_for_comment(body_markdown)
     parsed_markdown = MarkdownParser.new(fixed_body_markdown)
-    self.processed_html = parsed_markdown.finalize
+    self.processed_html = parsed_markdown.finalize(link_attributes: { rel: "nofollow" })
     wrap_timestamps_if_video_present!
     shorten_urls!
   end

spec/models/comment_spec.rb

@@ -79,6 +79,12 @@ RSpec.describe Comment, type: :model do
     expect(comment.processed_html.include?(">1:52:30</a>")).to eq(false)
   end
 
+  it "adds rel=nofollow to links" do
+    comment.body_markdown = "this is a comment with a link: http://dev.to"
+    comment.save
+    expect(comment.processed_html.include?('rel="nofollow"')).to eq(true)
+  end
+
   it "adds a mention url if user is mentioned like @mention" do
     comment.body_markdown = "Hello @#{user.username}, you are cool."
     comment.save