Next.js Daily: Turbopack Debug Fix and Lightning CSS Upgrade

Transcript

Good morning, this is Next.js Daily for February 16th, 2026.

Jiwon Choi merged a fix for Turbopack's debug build paths functionality that was failing with route groups. The issue occurred when using the debug-build-paths flag with route group patterns, causing a "Cannot find module for page" error. The root cause was a mismatch between how debug build paths preserved route group segments like "(group)" while Turbopack's route keys stripped them. The fix normalizes route group and parallel route segments in the debug build paths function to match Turbopack's behavior. This change includes comprehensive test coverage for both route groups and parallel routes.

Niklas Mischkulnig merged an upgrade to Lightning CSS version 1.31.0. The update required modifications to CSS compilation tests to accommodate changes in the new version. The upgrade was previously blocked by an upstream issue that has since been resolved, though one additional issue was identified during testing.

Swarnava Sengupta merged documentation improvements for the instrumentation register function. The changes explicitly clarify that Next.js waits for async instrumentation register functions to complete before handling incoming requests, with consistent wording between the guide and API reference documentation.

What's next: The team continues monitoring the newly identified Lightning CSS issue, and the Turbopack debug functionality now properly handles complex routing patterns including nested route groups and parallel routes.

That's your Next.js update for today.