Eagerly load swc bindings for wasm fallback for jest

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'