Performance degradation on pages with large content due to Project Studio CSS selectors

Summary

Users are experiencing significant performance degradation on pages with large discussions, commits with moderate changes, and likely other content-heavy pages following Project Studio design changes. The impact is severe enough to make core functionality like the sidebar and Duo Chat text area nearly unusable.

Impact

  • Sidebar navigation: Extremely laggy and unresponsive
  • General interface elements: Significant lag during interactions
  • Duo Chat text area: Almost unusable due to performance issues
  • Affected pages: Issues with large discussions, commits with moderate file changes, and potentially other pages

Reproducible Examples

Possible Cause

Performance Profile on Firefox.

The performance issues may be related to CSS selector usage in Project Studio, particularly:

  • Use of :has() pseudo-class in performance-critical rendering paths
  • Non-performant CSS selector patterns that trigger excessive style recalculation

Reference: MDN - :has() performance considerations

Steps to Reproduce

  1. Navigate to an issue with a large discussion thread (e.g., #577554 (closed))
  2. Attempt to interact with the sidebar or Duo Chat text area
  3. Observe significant lag and delayed response

Expected Behavior

Interface elements should remain responsive regardless of page content size.

Actual Behavior

Severe performance degradation making the interface difficult or impossible to use efficiently.

Edited by 🤖 GitLab Bot 🤖