next.js

fd5817d0 - feat: add --experimental-cpu-prof flag for dev, build, and start (#87946)

feat: add --experimental-cpu-prof flag for dev, build, and start (#87946) ## What Adds a `--experimental-cpu-prof` flag to `next dev`, `next build`, and `next start` commands to capture V8 CPU profiles for debugging performance bottlenecks. ## Why When investigating slow builds, slow dev server startups, or production server performance issues, having access to CPU profiles is invaluable. This provides a first-party way to capture these profiles without needing to manually set up the V8 inspector. ## How - Adds `--experimental-cpu-prof` flag to CLI commands - Uses V8's built-in CPU profiler via Node.js inspector module - Profiles are saved to `.next/cpu-profiles/` with descriptive filenames - Profiles are saved on process exit (Ctrl+C, SIGTERM, or normal exit) ### Profile files generated **`next dev`:** - `dev-main-*` - Parent process (dev server orchestration) - `dev-server-*` - Child server process (request handling and rendering) **`next build` (Turbopack):** - `build-main-*` - Main build orchestration process - `build-turbopack-*` - Turbopack compilation worker **`next build` (Webpack):** - `build-main-*` - Main build orchestration process - `build-webpack-client-*` - Client bundle compilation worker - `build-webpack-server-*` - Server bundle compilation worker - `build-webpack-edge-server-*` - Edge runtime compilation worker **`next start`:** - `start-main-*` - Production server process ## Changes addressing PR review comments - Removed signal handlers from `cpu-profile.ts` to prevent conflicts with CLI cleanup logic (telemetry, traces, etc.) - Added synchronous exit handler for non-signal process exits (errors, `process.exit()` calls) - CLI commands now explicitly call `saveCpuProfile()` as part of their cleanup before exiting - Replaced raw ANSI escape codes with `picocolors` library - Added comprehensive documentation about profile file naming for each command - Added build profiling test that verifies correct profile generation for both Turbopack and Webpack modes --------- Co-authored-by: Tim Neutkens <tim@timneutkens.nl>