Prepare @babel/core for asynchronicity

Gulpfile.js

@@ -183,6 +183,7 @@ function buildRollup(packages) {
               rollupCommonJs({
                 include: [
                   /node_modules/,
+                  "packages/babel-runtime/regenerator/**",
                   "packages/babel-preset-env/data/*.js",
                   // Rollup doesn't read export maps, so it loads the cjs fallback
                   "packages/babel-compat-data/*.js",

babel.config.js

@@ -14,6 +14,10 @@ module.exports = function(api) {
 
   let convertESM = true;
   let ignoreLib = true;
+  let includeRegeneratorRuntime = false;
+
+  let transformRuntimeOptions;
+
   const nodeVersion = "6.9";
   // The vast majority of our src files are modules, but we use
   // unambiguous to keep things simple until we get around to renaming
@@ -29,19 +33,19 @@ module.exports = function(api) {
 
   switch (env) {
     // Configs used during bundling builds.
-    case "rollup":
-      envOpts.targets = {
-        node: nodeVersion,
-      };
     case "standalone":
+      includeRegeneratorRuntime = true;
+      unambiguousSources.push("packages/babel-runtime/regenerator");
+    case "rollup":
       convertESM = false;
       ignoreLib = false;
+      // rollup-commonjs will converts node_modules to ESM
       unambiguousSources.push(
         "**/node_modules",
         "packages/babel-preset-env/data",
         "packages/babel-compat-data"
       );
-      // targets to browserslists: defaults
+      if (env === "rollup") envOpts.targets = { node: nodeVersion };
       break;
     case "production":
       // Config during builds before publish.
@@ -62,6 +66,16 @@ module.exports = function(api) {
       break;
   }
 
+  if (includeRegeneratorRuntime) {
+    const babelRuntimePkgPath = require.resolve("@babel/runtime/package.json");
+
+    transformRuntimeOptions = {
+      helpers: false, // Helpers are handled by rollup when needed
+      regenerator: true,
+      version: require(babelRuntimePkgPath).version,
+    };
+  }
+
   const config = {
     // Our dependencies are all standard CommonJS, along with all sorts of
     // other random files in Babel's codebase, so we use script as the default,
@@ -119,6 +133,10 @@ module.exports = function(api) {
         test: unambiguousSources,
         sourceType: "unambiguous",
       },
+      includeRegeneratorRuntime && {
+        exclude: /regenerator-runtime/,
+        plugins: [["@babel/transform-runtime", transformRuntimeOptions]],
+      },
     ].filter(Boolean),
   };
 

lib/third-party-libs.js.flow

@@ -4,6 +4,7 @@
 
 declare module "resolve" {
   declare export default {
+    (string, {| basedir: string |}, (err: ?Error, res: string) => void): void;
     sync: (string, {| basedir: string |}) => string;
   };
 }

packages/babel-core/package.json

@@ -49,6 +49,7 @@
     "@babel/types": "^7.7.4",
     "convert-source-map": "^1.7.0",
     "debug": "^4.1.0",
+    "gensync": "^1.0.0-beta.1",
     "json5": "^2.1.0",
     "lodash": "^4.17.13",
     "resolve": "^1.3.2",