#!/usr/bin/env node

/**

* CLI Startup Tracer

*

* Uses the V8 Inspector API to trace module loading at CLI startup.

* This helps identify which modules are being loaded eagerly.

*

* Usage:

* node scripts/trace-cli-startup.js [--command=dev|build|--help]

*/

const inspector = require('inspector')

const fs = require('fs')

const path = require('path')

const args = process.argv.slice(2)

const getArg = (name, defaultValue) => {

const arg = args.find((a) => a.startsWith(`--${name}=`))

return arg ? arg.split('=')[1] : defaultValue

}

const command = getArg('command', '--help')

const outputDir = path.join(process.cwd(), 'profiles')

if (!fs.existsSync(outputDir)) {

fs.mkdirSync(outputDir, { recursive: true })

}

console.log('\x1b[34m=== Next.js CLI Startup Trace ===\x1b[0m')

console.log(`Command: next ${command}`)

console.log(`Output directory: ${outputDir}`)

console.log('')

// Start CPU profiling

const session = new inspector.Session()

session.connect()

// Track module loading via require hook

const Module = require('module')

const originalRequire = Module.prototype.require

const loadedModules = []

const moduleLoadTimes = []

Module.prototype.require = function (id) {

const start = process.hrtime.bigint()

const result = originalRequire.apply(this, arguments)

const end = process.hrtime.bigint()

const durationMs = Number(end - start) / 1e6

// Get the resolved path

let resolvedPath = id

try {

resolvedPath = require.resolve(id, { paths: [this.path || process.cwd()] })

} catch {}

// Filter to show only Next.js-related modules

if (resolvedPath.includes('next/dist/') || resolvedPath.includes('@next/')) {

const shortPath = resolvedPath.includes('next/dist/')

? resolvedPath.split('next/dist/')[1]

: resolvedPath

if (!loadedModules.includes(shortPath)) {

loadedModules.push(shortPath)

moduleLoadTimes.push({ module: shortPath, time: durationMs })

}

}

return result

}

// Save original process.exit and intercept to prevent CLI from exiting mid-profile

const originalExit = process.exit

process.exit = () => {

// Don't actually exit during profiling - we want to capture the full profile

}

// Start profiling

session.post('Profiler.enable', () => {

session.post('Profiler.start', () => {

console.log('Starting CLI with profiling...')

console.log('')

const startTime = process.hrtime.bigint()

// Load the CLI

try {

process.argv = [process.argv[0], 'next', command]

require('../packages/next/dist/bin/next')

} catch (e) {

// Expected - CLI might throw

}

const endTime = process.hrtime.bigint()

const totalMs = Number(endTime - startTime) / 1e6

// Stop profiling and save

session.post('Profiler.stop', (err, { profile }) => {

if (err) {

console.error('Error stopping profiler:', err)

} else {

const profilePath = path.join(

outputDir,

`cli-startup-${Date.now()}.cpuprofile`

)

fs.writeFileSync(profilePath, JSON.stringify(profile))

console.log(`\x1b[32mProfile saved:\x1b[0m ${profilePath}`)

}

// Print results

console.log('')

console.log(`\x1b[32mTotal startup time:\x1b[0m ${totalMs.toFixed(2)}ms`)

console.log('')

console.log(`\x1b[33mModules loaded (${loadedModules.length}):\x1b[0m`)

console.log('='.repeat(70))

// Sort by load time

moduleLoadTimes.sort((a, b) => b.time - a.time)

moduleLoadTimes.slice(0, 30).forEach((m, i) => {

const timeStr =

m.time > 1

? `${m.time.toFixed(1)}ms`

: `${(m.time * 1000).toFixed(0)}μs`

console.log(`${String(i + 1).padStart(2)}. ${m.module} (${timeStr})`)

})

console.log('')

console.log(`\x1b[33mAll loaded modules:\x1b[0m`)

console.log(loadedModules.join('\n'))

// Restore original require

Module.prototype.require = originalRequire

session.disconnect()

// Exit cleanly now that profiling is complete

originalExit(0)

})

})

})