## 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
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Co-authored-by: Tim Neutkens <tim@timneutkens.nl>
Tim Neutkens