feat(next/config): enable experimental swcTrace

packages/next-swc/crates/core/Cargo.toml

@@ -27,8 +27,7 @@ swc_common = { version = "0.17.19", features = ["concurrent", "sourcemap"] }
 swc_ecma_loader = { version = "0.29.0", features = ["node", "lru"] }
 swc_ecmascript = { version = "0.143.0", features = ["codegen", "minifier", "optimization", "parser", "react", "transforms", "typescript", "utils", "visit"] }
 swc_cached = "0.1.1"
-tracing = { version = "0.1.32", features = ["release_max_level_off"] }
-
+tracing = { version = "0.1.32", features = ["release_max_level_info"] }
 
 [dev-dependencies]
 swc_ecma_transforms_testing = "0.77.0"

packages/next-swc/crates/emotion/Cargo.toml

@@ -21,6 +21,8 @@ sourcemap = "6.0.1"
 swc_atoms = "0.2.11"
 swc_common = { version = "0.17.19", features = ["concurrent", "sourcemap"] }
 swc_ecmascript = { version = "0.143.0", features = ["codegen", "utils", "visit"] }
+swc_trace_macro = "0.1.1"
+tracing = { version = "0.1.32", features = ["release_max_level_info"] }
 
 [dev-dependencies]
 swc_ecma_transforms_testing = "0.77.0"

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

@@ -5,3 +5,4 @@ export function minify(src: string, options: any): Promise<string>
 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

packages/next/build/swc/index.js

@@ -192,6 +192,8 @@ function loadNative() {
       },
 
       getTargetTriple: bindings.getTargetTriple,
+      initCustomTraceSubscriber: bindings.initCustomTraceSubscriber,
+      teardownTraceSubscriber: bindings.teardownTraceSubscriber,
     }
     return nativeBindings
   }
@@ -251,3 +253,35 @@ export function getBinaryMetadata() {
     target: bindings?.getTargetTriple?.(),
   }
 }
+
+/**
+ * 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) {
+      // Wasm binary doesn't support trace emission
+      let bindings = loadNative()
+      guard = bindings.initCustomTraceSubscriber(filename)
+    }
+
+    return guard
+  }
+})()
+
+export const teardownTraceSubscriber = (() => {
+  let bindings
+
+  return (guard) => {
+    if (!bindings && !!guard) {
+      // Wasm binary doesn't support trace emission
+      bindings = loadNative()
+      return bindings.teardownTraceSubscriber(guard)
+    }
+  }
+})()

packages/next/build/webpack-config.ts

@@ -88,6 +88,22 @@ 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')
@@ -439,6 +455,20 @@ export default async function getBaseWebpackConfig(
   }
 
   const getBabelOrSwcLoader = (isMiddleware: boolean) => {
+    if (
+      useSWCLoader &&
+      config?.experimental?.swcTrace?.enabled &&
+      !swcTraceFlushGuard
+    ) {
+      // 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?.(
+        config?.experimental?.swcTrace?.traceFileName
+      )
+    }
+
     return useSWCLoader
       ? {
           loader: 'next-swc-loader',

packages/next/server/config-shared.ts

@@ -128,6 +128,10 @@ export interface ExperimentalConfig {
       skipDefaultConversion?: boolean
     }
   >
+  swcTrace?: {
+    enabled: boolean
+    traceFileName?: string
+  }
 }
 
 /**