Avoid dynamic import when it's not needed (#14192)

nicolo-ribaudo · web-flow · commit 2ea90542bcd8 · 2022-01-22T10:12:35.000+01:00
diff --git a/packages/babel-core/src/config/files/import-meta-resolve.ts b/packages/babel-core/src/config/files/import-meta-resolve.ts
@@ -10,33 +10,38 @@ try {
 } catch {}
 
 // import.meta.resolve is only available in ESM, but this file is compiled to CJS.
-// We can extract ir using dynamic import.
-const resolveP =
+// We can extract it using dynamic import.
+const importMetaResolveP: Promise<ImportMeta["resolve"]> =
   import_ &&
   // Due to a Node.js/V8 bug (https://github.com/nodejs/node/issues/35889), we cannot
-  // use dynamic import when running in the default Jest environment because it
-  // uses vm.SourceTextModule.
-  // Jest defines globalThis["jest-symbol-do-not-touch"] in
-  // https://github.com/facebook/jest/blob/11d79ec096a25851124356095d60352f6ca2824e/packages/jest-util/src/installCommonGlobals.ts#L49
-  // which is called by
-  // https://github.com/facebook/jest/blob/11d79ec096a25851124356095d60352f6ca2824e/packages/jest-environment-node/src/index.ts#L85
+  // use always dynamic import because it segfaults when running in a Node.js `vm` context,
+  // which is used by the default Jest environment and by webpack-cli.
   //
-  // Note that our Jest runner doesn't have this problem, because it runs ESM in the default
-  // Node.js context rather than using the `vm` module.
+  // However, import.meta.resolve is experimental and only enabled when Node.js is run
+  // with the `--experimental-import-meta-resolve` flag: we can avoid calling import()
+  // when that flag is not enabled, so that the default behavior never segfaults.
   //
-  // When V8 fixes this bug, we can remove this check. We usually don't have package-specific hacks,
-  // but Jest is a big Babel consumer widely used in the community and they cannot workaround
-  // this problem on their side.
-  !Object.hasOwnProperty.call(global, "jest-symbol-do-not-touch")
+  // Hopefully, before Node.js unflags import.meta.resolve, either:
+  // - we will move to ESM, so that we have direct access to import.meta.resolve, or
+  // - the V8 bug will be fixed so that we can safely use dynamic import by default.
+  //
+  // I (@nicolo-ribaudo) am really anoyed by this bug, because there is no known
+  // work-around other than "don't use dynamic import if you are running in a `vm` context",
+  // but there is no reliable way to detect it (you cannot try/catch segfaults).
+  //
+  // This is the only place where we *need* to use dynamic import because we need to access
+  // an ES module. All the other places will first try using require() and *then*, if
+  // it throws because it's a module, will fallback to import().
+  process.execArgv.includes("--experimental-import-meta-resolve")
     ? import_("data:text/javascript,export default import.meta.resolve").then(
-        // Since import.meta.resolve is unstable and only available when
-        // using the --experimental-import-meta-resolve flag, we almost
-        // always use the polyfill for now.
         m => m.default || polyfill,
         () => polyfill,
       )
     : Promise.resolve(polyfill);
 
-export default function getImportMetaResolve(): Promise<ImportMeta["resolve"]> {
-  return resolveP;
+export default async function resolve(
+  specifier: Parameters<ImportMeta["resolve"]>[0],
+  parent?: Parameters<ImportMeta["resolve"]>[1],
+): ReturnType<ImportMeta["resolve"]> {
+  return (await importMetaResolveP)(specifier, parent);
 }
diff --git a/packages/babel-core/src/config/files/plugins.ts b/packages/babel-core/src/config/files/plugins.ts
@@ -9,7 +9,7 @@ import { isAsync } from "../../gensync-utils/async";
 import loadCjsOrMjsDefault, { supportsESM } from "./module-types";
 import { fileURLToPath, pathToFileURL } from "url";
 
-import getImportMetaResolve from "./import-meta-resolve";
+import importMetaResolve from "./import-meta-resolve";
 
 import { createRequire } from "module";
 const require = createRequire(import.meta.url);
@@ -134,7 +134,6 @@ async function tryImportMetaResolve(
   id: Parameters<ImportMeta["resolve"]>[0],
   options: Parameters<ImportMeta["resolve"]>[1],
 ): Promise<Result<string>> {
-  const importMetaResolve = await getImportMetaResolve();
   try {
     return { error: null, value: await importMetaResolve(id, options) };
   } catch (error) {
