Fix a race condition in @babel/core (#14843)

Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>

Gulpfile.mjs

@@ -265,7 +265,7 @@ async function buildBabel(useWorker, ignore = []) {
     const dest = "./" + mapSrcToLib(file.slice(2));
     promises.push(worker.transform(file, dest));
   }
-  return Promise.all(promises).finally(() => {
+  return Promise.allSettled(promises).finally(() => {
     if (worker.end !== undefined) {
       worker.end();
     }

babel-worker.cjs

@@ -1,4 +1,4 @@
-const { transformSync } = require("@babel/core");
+const { transformAsync } = require("@babel/core");
 const { mkdirSync, statSync, readFileSync, writeFileSync } = require("fs");
 const { dirname } = require("path");
 const { log } = require("./scripts/utils/logger.cjs");
@@ -32,7 +32,7 @@ exports.transform = async function transform(src, dest) {
   }
   log(`Compiling '${chalk.cyan(src)}'...`);
   const content = readFileSync(src, { encoding: "utf8" });
-  const { code } = transformSync(content, {
+  const { code } = await transformAsync(content, {
     filename: src,
     caller: {
       // We have wrapped packages/babel-core/src/config/files/configuration.js with feature detection

packages/babel-core/src/config/config-descriptors.ts

@@ -1,6 +1,5 @@
-import gensync from "gensync";
-
-import type { Handler } from "gensync";
+import gensync, { type Handler } from "gensync";
+import { once } from "../gensync-utils/functional";
 
 import { loadPlugin, loadPreset } from "./files";
 
@@ -123,35 +122,22 @@ export function createUncachedDescriptors(
   options: ValidatedOptions,
   alias: string,
 ): OptionsAndDescriptors {
-  // The returned result here is cached to represent a config object in
-  // memory, so we build and memoize the descriptors to ensure the same
-  // values are returned consistently.
-  let plugins: UnloadedDescriptor[];
-  let presets: UnloadedDescriptor[];
-
   return {
     options: optionsWithResolvedBrowserslistConfigFile(options, dirname),
-    *plugins() {
-      if (!plugins) {
-        plugins = yield* createPluginDescriptors(
-          options.plugins || [],
-          dirname,
-          alias,
-        );
-      }
-      return plugins;
-    },
-    *presets() {
-      if (!presets) {
-        presets = yield* createPresetDescriptors(
-          options.presets || [],
-          dirname,
-          alias,
-          !!options.passPerPreset,
-        );
-      }
-      return presets;
-    },
+    // The returned result here is cached to represent a config object in
+    // memory, so we build and memoize the descriptors to ensure the same
+    // values are returned consistently.
+    plugins: once(() =>
+      createPluginDescriptors(options.plugins || [], dirname, alias),
+    ),
+    presets: once(() =>
+      createPresetDescriptors(
+        options.presets || [],
+        dirname,
+        alias,
+        !!options.passPerPreset,
+      ),
+    ),
   };
 }
 

packages/babel-core/src/gensync-utils/functional.ts

@@ -0,0 +1,31 @@
+import type { Handler } from "gensync";
+
+import { isAsync, waitFor } from "./async";
+
+export function once<R>(fn: () => Handler<R>): () => Handler<R> {
+  let result: R;
+  let resultP: Promise<R>;
+  return function* () {
+    if (result) return result;
+    if (!(yield* isAsync())) return (result = yield* fn());
+    if (resultP) return yield* waitFor(resultP);
+
+    let resolve: (result: R) => void, reject: (error: unknown) => void;
+    resultP = new Promise((res, rej) => {
+      resolve = res;
+      reject = rej;
+    });
+
+    try {
+      result = yield* fn();
+      // Avoid keeping the promise around
+      // now that we have the result.
+      resultP = null;
+      resolve(result);
+      return result;
+    } catch (error) {
+      reject(error);
+      throw error;
+    }
+  };
+}