Eagerly load swc bindings for wasm fallback for jest (#36784)

Follow-up to #36612 this updates to eagerly load the swc bindings unless babel is being used so that we don't wait for the transform calls to initialize swc. Eagerly loading in jest also allows us to fallback to the wasm bindings when previously we couldn't since they needed to wait for the import.

packages/next/build/jest/jest.ts

@@ -5,6 +5,7 @@ import { PHASE_TEST } from '../../shared/lib/constants'
 import loadJsConfig from '../load-jsconfig'
 import * as Log from '../output/log'
 import { findPagesDir } from '../../lib/find-pages-dir'
+import { loadBindings, lockfilePatchPromise } from '../swc'
 
 async function getConfig(dir: string) {
   const conf = await loadConfig(PHASE_TEST, dir)
@@ -72,6 +73,13 @@ export default function nextJest(options: { dir?: string } = {}) {
           ? await customJestConfig()
           : customJestConfig) ?? {}
 
+      // eagerly load swc bindings instead of waiting for transform calls
+      await loadBindings()
+
+      if (lockfilePatchPromise.cur) {
+        await lockfilePatchPromise.cur
+      }
+
       return {
         ...resolvedJestConfig,
 

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

@@ -8,3 +8,4 @@ export function parse(src: string, options: any): any
 export const lockfilePatchPromise: { cur?: Promise<void> }
 export function initCustomTraceSubscriber(traceFileName?: string): void
 export function teardownTraceSubscriber(): void
+export function loadBindings(): Promise<void>

packages/next/build/swc/index.js

@@ -20,7 +20,7 @@ let pendingBindings
 let swcTraceFlushGuard
 export const lockfilePatchPromise = {}
 
-async function loadBindings() {
+export async function loadBindings() {
   if (pendingBindings) {
     return pendingBindings
   }
@@ -87,6 +87,12 @@ function loadBindingsSync() {
     attempts = attempts.concat(a)
   }
 
+  // we can leverage the wasm bindings if they are already
+  // loaded
+  if (wasmBindings) {
+    return wasmBindings
+  }
+
   logLoadFailure(attempts)
 }
 
@@ -133,16 +139,24 @@ async function loadWasm(importPath = '') {
       wasmBindings = {
         isWasm: true,
         transform(src, options) {
-          return Promise.resolve(
-            bindings.transformSync(src.toString(), options)
-          )
+          return bindings.transformSync(src.toString(), options)
+        },
+        transformSync(src, options) {
+          return bindings.transformSync(src.toString(), options)
         },
         minify(src, options) {
-          return Promise.resolve(bindings.minifySync(src.toString(), options))
+          return bindings.minifySync(src.toString(), options)
+        },
+        minifySync(src, options) {
+          return bindings.minifySync(src.toString(), options)
         },
         parse(src, options) {
           const astStr = bindings.parseSync(src.toString(), options)
-          return Promise.resolve(astStr)
+          return astStr
+        },
+        parseSync(src, options) {
+          const astStr = bindings.parseSync(src.toString(), options)
+          return astStr
         },
         getTargetTriple() {
           return undefined

packages/next/build/webpack-config.ts

@@ -54,6 +54,7 @@ import { withoutRSCExtensions } from './utils'
 import browserslist from 'next/dist/compiled/browserslist'
 import loadJsConfig from './load-jsconfig'
 import { getMiddlewareSourceMapPlugins } from './webpack/plugins/middleware-source-maps-plugin'
+import { loadBindings } from './swc'
 
 const watchOptions = Object.freeze({
   aggregateTimeout: 5,
@@ -432,6 +433,11 @@ export default async function getBaseWebpackConfig(
     loggedSwcDisabled = true
   }
 
+  // eagerly load swc bindings instead of waiting for transform calls
+  if (!babelConfigFile && isClient) {
+    await loadBindings()
+  }
+
   if (!loggedIgnoredCompilerOptions && !useSWCLoader && config.compiler) {
     Log.info(
       '`compiler` options in `next.config.js` will be ignored while using Babel https://nextjs.org/docs/messages/ignored-compiler-options'