refactor(swc/trace): adjust teardown

packages/next/build/index.ts

@@ -113,6 +113,7 @@ import type { webpack5 as webpack } from 'next/dist/compiled/webpack/webpack'
 import { recursiveCopy } from '../lib/recursive-copy'
 import { shouldUseReactRoot } from '../server/config'
 import { recursiveReadDir } from '../lib/recursive-readdir'
+import { teardownTraceSubscriber } from './swc'
 
 export type SsgRoute = {
   initialRevalidateSeconds: number | false
@@ -2134,6 +2135,7 @@ export default async function build(
 
   // Ensure all traces are flushed before finishing the command
   await flushAllTraces()
+  teardownTraceSubscriber()
 
   return buildResult
 }

packages/next/build/output/store.ts

@@ -2,7 +2,7 @@ import createStore from 'next/dist/compiled/unistore'
 import stripAnsi from 'next/dist/compiled/strip-ansi'
 import { flushAllTraces } from '../../trace'
 import { getUnresolvedModuleFromError } from '../utils'
-
+import { teardownTraceSubscriber } from '../swc'
 import * as Log from './log'
 
 export type OutputState =
@@ -100,6 +100,7 @@ store.subscribe((state) => {
 
     // Ensure traces are flushed after each compile in development mode
     flushAllTraces()
+    teardownTraceSubscriber()
     return
   }
 
@@ -126,6 +127,7 @@ store.subscribe((state) => {
     Log.warn(state.warnings.join('\n\n'))
     // Ensure traces are flushed after each compile in development mode
     flushAllTraces()
+    teardownTraceSubscriber()
     return
   }
 
@@ -141,4 +143,5 @@ store.subscribe((state) => {
   )
   // Ensure traces are flushed after each compile in development mode
   flushAllTraces()
+  teardownTraceSubscriber()
 })

packages/next/build/swc/index.d.ts

@@ -6,3 +6,4 @@ export function minifySync(src: string, options: any): string
 export function bundle(options: any): Promise<any>
 export function parse(src: string, options: any): any
 export function initCustomTraceSubscriber(traceFileName?: string): void
+export function teardownTraceSubscriber(): void

packages/next/build/swc/index.js

@@ -9,6 +9,7 @@ const triples = platformArchTriples[PlatformName][ArchName] || []
 
 let nativeBindings
 let wasmBindings
+let swcTraceFlushGuard
 
 async function loadBindings() {
   let attempts = []
@@ -258,31 +259,39 @@ export function getBinaryMetadata() {
 /**
  * Initialize trace subscriber to emit traces.
  *
- * Returns an internal object to guard async flush emission if subscriber is initialized, caller should manually
- * tear it down via `teardownTraceSubscriber`.
  */
 export const initCustomTraceSubscriber = (() => {
-  let guard
-
   return (filename) => {
-    if (!guard) {
+    if (!swcTraceFlushGuard) {
       // Wasm binary doesn't support trace emission
       let bindings = loadNative()
-      guard = bindings.initCustomTraceSubscriber(filename)
+      swcTraceFlushGuard = bindings.initCustomTraceSubscriber(filename)
     }
-
-    return guard
   }
 })()
 
+/**
+ * Teardown swc's trace subscriber if there's an initialized flush guard exists.
+ *
+ * This is workaround to amend behavior with process.exit
+ * (https://github.com/vercel/next.js/blob/4db8c49cc31e4fc182391fae6903fb5ef4e8c66e/packages/next/bin/next.ts#L134=)
+ * seems preventing napi's cleanup hook execution (https://github.com/swc-project/swc/blob/main/crates/node/src/util.rs#L48-L51=),
+ *
+ * instead parent process manually drops guard when process gets signal to exit.
+ */
 export const teardownTraceSubscriber = (() => {
-  let bindings
-
-  return (guard) => {
-    if (!bindings && !!guard) {
-      // Wasm binary doesn't support trace emission
-      bindings = loadNative()
-      return bindings.teardownTraceSubscriber(guard)
+  let flushed = false
+  return () => {
+    if (!flushed) {
+      flushed = true
+      try {
+        let bindings = loadNative()
+        if (swcTraceFlushGuard) {
+          bindings.teardownTraceSubscriber(swcTraceFlushGuard)
+        }
+      } catch (e) {
+        // Suppress exceptions, this fn allows to fail to load native bindings
+      }
     }
   }
 })()

packages/next/build/webpack-config.ts

@@ -87,22 +87,6 @@ const devtoolRevertWarning = execOnce(
 
 let loggedSwcDisabled = false
 let loggedIgnoredCompilerOptions = false
-let swcTraceFlushGuard: unknown = null
-
-/**
- * Teardown swc's trace subscriber if there's an initialized flush guard exists.
- *
- * This is workaround to amend behavior with process.exit
- * (https://github.com/vercel/next.js/blob/4db8c49cc31e4fc182391fae6903fb5ef4e8c66e/packages/next/bin/next.ts#L134=)
- * seems preventing napi's cleanup hook execution (https://github.com/swc-project/swc/blob/main/crates/node/src/util.rs#L48-L51=),
- *
- * instead parent process manually drops guard when process gets signal to exit.
- */
-process.on('exit', () => {
-  if (swcTraceFlushGuard) {
-    require('./swc')?.teardownTraceSubscriber?.(swcTraceFlushGuard)
-  }
-})
 
 function getOptimizedAliases(): { [pkg: string]: string } {
   const stubWindowFetch = path.join(__dirname, 'polyfills', 'fetch', 'index.js')
@@ -451,22 +435,14 @@ export default async function getBaseWebpackConfig(
     loggedIgnoredCompilerOptions = true
   }
 
-  const getBabelOrSwcLoader = (buildDir: string) => {
-    if (
-      useSWCLoader &&
-      config?.experimental?.swcTraceProfiling &&
-      !swcTraceFlushGuard
-    ) {
+  const getBabelOrSwcLoader = () => {
+    if (useSWCLoader && config?.experimental?.swcTraceProfiling) {
       // This will init subscribers once only in a single process lifecycle,
       // even though it can be called multiple times.
       // Subscriber need to be initialized _before_ any actual swc's call (transform, etcs)
       // to collect correct trace spans when they are called.
-      swcTraceFlushGuard = require('./swc')?.initCustomTraceSubscriber?.(
-        path.join(
-          buildDir,
-          config.distDir,
-          `swc-trace-profile-${Date.now()}.json`
-        )
+      require('./swc')?.initCustomTraceSubscriber?.(
+        path.join(config.distDir, `swc-trace-profile-${Date.now()}.json`)
       )
     }
 
@@ -498,7 +474,7 @@ export default async function getBaseWebpackConfig(
   }
 
   const defaultLoaders = {
-    babel: getBabelOrSwcLoader(false),
+    babel: getBabelOrSwcLoader(),
   }
 
   const rawPageExtensions = hasServerComponents
@@ -1251,7 +1227,7 @@ export default async function getBaseWebpackConfig(
             {
               ...codeCondition,
               issuerLayer: 'middleware',
-              use: getBabelOrSwcLoader(true),
+              use: getBabelOrSwcLoader(),
             },
             {
               ...codeCondition,