Fix NODE_OPTIONS='--inspect' not running expected

packages/next/src/server/lib/start-server.ts

@@ -7,7 +7,11 @@ import { isIPv6 } from 'net'
 import * as Log from '../../build/output/log'
 import { normalizeRepeatedSlashes } from '../../shared/lib/utils'
 import { initialEnv } from '@next/env'
-import { genRouterWorkerExecArgv, getNodeOptionsWithoutInspect } from './utils'
+import {
+  genRouterWorkerExecArgv,
+  getDebugPort,
+  getNodeOptionsWithoutInspect,
+} from './utils'
 
 export interface StartServerOptions {
   dir: string
@@ -155,6 +159,15 @@ export async function startServer({
 
       const appUrl = `http://${host}:${port}`
 
+      if (isNodeDebugging) {
+        const debugPort = getDebugPort()
+        Log.info(
+          `the --inspect${
+            isNodeDebugging === 'brk' ? '-brk' : ''
+          } option was detected, the Next.js proxy server should be inspected at port ${debugPort}.`
+        )
+      }
+
       Log.ready(
         `started server on ${normalizedHostname}${
           (port + '').startsWith(':') ? '' : ':'

packages/next/src/server/lib/utils.ts

@@ -1,5 +1,5 @@
 import type arg from 'next/dist/compiled/arg/index.js'
-import { getFreePort } from './worker-utils'
+import * as Log from '../../build/output/log'
 
 export function printAndExit(message: string, code = 1) {
   if (code === 0) {
@@ -11,6 +11,19 @@ export function printAndExit(message: string, code = 1) {
   process.exit(code)
 }
 
+export const getDebugPort = () => {
+  const debugPortStr =
+    process.execArgv
+      .find(
+        (localArg) =>
+          localArg.startsWith('--inspect') ||
+          localArg.startsWith('--inspect-brk')
+      )
+      ?.split('=')[1] ??
+    process.env.NODE_OPTIONS?.match?.(/--inspect(-brk)?(=(\S+))?( |$)/)?.[3]
+  return debugPortStr ? parseInt(debugPortStr, 10) : 9229
+}
+
 export const genRouterWorkerExecArgv = async (
   isNodeDebugging: boolean | 'brk'
 ) => {
@@ -21,9 +34,18 @@ export const genRouterWorkerExecArgv = async (
   })
 
   if (isNodeDebugging) {
-    const debugPort = await getFreePort()
+    const isDebuggingWithBrk = isNodeDebugging === 'brk'
+
+    let debugPort = getDebugPort() + 1
+
+    Log.info(
+      `the --inspect${
+        isDebuggingWithBrk ? '-brk' : ''
+      } option was detected, the Next.js routing server should be inspected at port ${debugPort}.`
+    )
+
     execArgv.push(
-      `--inspect${isNodeDebugging === 'brk' ? '-brk' : ''}=${debugPort + 1}`
+      `--inspect${isNodeDebugging === 'brk' ? '-brk' : ''}=${debugPort}`
     )
   }
 

packages/next/src/server/lib/worker-utils.ts

@@ -1,5 +1,6 @@
 import * as Log from '../../build/output/log'
 import http from 'http'
+import { getDebugPort } from './utils'
 
 export const getFreePort = async (): Promise<number> => {
   return new Promise((resolve, reject) => {
@@ -28,7 +29,6 @@ export const genRenderExecArgv = async (
   })
 
   if (isNodeDebugging) {
-    const debugPort = await getFreePort()
     const isDebugging =
       process.execArgv.some((localArg) => localArg.startsWith('--inspect')) ||
       process.env.NODE_OPTIONS?.match?.(/--inspect(=\S+)?( |$)/)
@@ -39,16 +39,18 @@ export const genRenderExecArgv = async (
       ) || process.env.NODE_OPTIONS?.match?.(/--inspect-brk(=\S+)?( |$)/)
 
     if (isDebugging || isDebuggingWithBrk) {
+      let debugPort = getDebugPort()
+
+      debugPort += type === 'pages' ? 1 : 2
+
       Log.info(
         `the --inspect${
           isDebuggingWithBrk ? '-brk' : ''
         } option was detected, the Next.js server${
           type === 'pages' ? ' for pages' : type === 'app' ? ' for app' : ''
         } should be inspected at port ${debugPort}.`
       )
-    }
 
-    if (isDebugging || isDebuggingWithBrk) {
       execArgv.push(`--inspect${isDebuggingWithBrk ? '-brk' : ''}=${debugPort}`)
     }
   }