Merge branch 'fix-inline-filter-speed' into 'master'

Fix serious performance bug with rendering Markdown with InlineDiffFilter

Nokogiri's `node.replace` was being unnecessarily called for every text node in
the document due to a comparison bug. The code previously was comparing the
HTML representation of the full document against the text node, which would
always fail. Fix the comparison to just compare the modified text.

Closes #18011 


See merge request !4392

2 files changed, 9 insertions, 4 deletions

diff --git a/CHANGELOG b/CHANGELOG
index 6f91dfcfb68..2467a45c0eb 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -31,6 +31,7 @@ v 8.9.0 (unreleased)
 v 8.8.3
   - Fix incorrect links on pipeline page when merge request created from fork
   - Fix gitlab importer failing to import new projects due to missing credentials
+  - Fix serious performance bug with rendering Markdown with InlineDiffFilter
   - Fix import URL migration not rescuing with the correct Error
   - In search results, only show notes on confidential issues that the user has access to
   - Fix health check access token changing due to old application settings being used
diff --git a/lib/banzai/filter/inline_diff_filter.rb b/lib/banzai/filter/inline_diff_filter.rb
index 9e75edd4d4c..beb21b19ab3 100644
--- a/lib/banzai/filter/inline_diff_filter.rb
+++ b/lib/banzai/filter/inline_diff_filter.rb
@@ -8,15 +8,19 @@ module Banzai
           next if has_ancestor?(node, IGNORED_ANCESTOR_TAGS)
 
           content = node.to_html
-          content = content.gsub(/(?:\[\-(.*?)\-\]|\{\-(.*?)\-\})/, '<span class="idiff left right deletion">\1\2</span>')
-          content = content.gsub(/(?:\[\+(.*?)\+\]|\{\+(.*?)\+\})/, '<span class="idiff left right addition">\1\2</span>')
+          html_content = inline_diff_filter(content)
 
-          next if html == content
+          next if content == html_content
 
-          node.replace(content)
+          node.replace(html_content)
         end
         doc
       end
+
+      def inline_diff_filter(text)
+        html_content = text.gsub(/(?:\[\-(.*?)\-\]|\{\-(.*?)\-\})/, '<span class="idiff left right deletion">\1\2</span>')
+        html_content.gsub(/(?:\[\+(.*?)\+\]|\{\+(.*?)\+\})/, '<span class="idiff left right addition">\1\2</span>')
+      end
     end
   end
 end