Use the new "extensions" option in @babel/register

packages/babel-register/src/node.js

@@ -7,6 +7,35 @@ import { OptionManager, DEFAULT_EXTENSIONS } from "@babel/core";
 import { addHook } from "pirates";
 import fs from "fs";
 import path from "path";
+import { Module } from "module";
+
+// The "pirates" library, that we use to register require hooks, does
+// not allow hooking into all the loaded files, but requries us to
+// specify the extensions upfront.
+// In order to hook into all of them, we need to do two things:
+//  1) Add hooks for all the already registered extensions, defined in
+//     Module._extensions. By doing so, we can shadow the loaders already
+//     defined.
+//  2) Node throws an error when requireing .mjs unless a hook has been
+//     defined. For compatibility reason (@babel/register can load .mjs files)
+//     we add the extension to the list.
+//  3) Node fallbacks to the .js loader for unknown extensions, however
+//     pirates will only run our hook if it actually matches the extension
+//     (without a fallback mechanism). However, it checks if an extension
+//     has been registered by checking 'extensions.indexOf(...)'.
+//     And... we can make it always return true! ^-^
+// Since this is not technically part of the public API of "pirates", the
+// version in package.json is fixed to avoid untested updates.
+const NODE_EXTENSIONS = Object.defineProperty(
+  Object.keys(Module._extensions).concat(".mjs"),
+  "indexOf",
+  {
+    configurable: true,
+    writable: true,
+    enumerable: false,
+    value: () => true,
+  },
+);
 
 const maps = {};
 let transformOpts = {};
@@ -47,7 +76,7 @@ function compile(code, filename) {
     },
   );
 
-  // Bail out ASAP if the file has been ignored.
+  // Bail out ASAP if the file has been ignored or has an unsupported extension
   if (opts === null) return code;
 
   let cacheKey = `${JSON.stringify(opts)}:${babel.version}`;
@@ -106,11 +135,10 @@ export function revert() {
 register();
 
 export default function register(opts?: Object = {}) {
+  hookExtensions(NODE_EXTENSIONS);
+
   // Clone to avoid mutating the arguments object with the 'delete's below.
-  opts = {
-    ...opts,
-  };
-  hookExtensions(opts.extensions || DEFAULT_EXTENSIONS);
+  opts = { ...opts };
 
   if (opts.cache === false && cache) {
     registerCache.clear();
@@ -120,10 +148,12 @@ export default function register(opts?: Object = {}) {
     cache = registerCache.get();
   }
 
-  delete opts.extensions;
   delete opts.cache;
 
   transformOpts = {
+    // TODO(Babel 8): At some point @babel/core will default to DEFAULT_EXTENSIONS
+    // instead of ["*"], and we can avoid setting it here.
+    extensions: DEFAULT_EXTENSIONS,
     ...opts,
     caller: {
       name: "@babel/register",

packages/babel-register/test/fixtures/integration/default-extensions/babel.config.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["../logger"]
+}

packages/babel-register/test/fixtures/integration/default-extensions/foo.cjs

@@ -0,0 +1 @@
+console.log("DONE: foo.cjs");

packages/babel-register/test/fixtures/integration/default-extensions/foo.es

@@ -0,0 +1 @@
+console.log("DONE: foo.es");

packages/babel-register/test/fixtures/integration/default-extensions/foo.es6

@@ -0,0 +1 @@
+console.log("DONE: foo.es6");

packages/babel-register/test/fixtures/integration/default-extensions/foo.jsx

@@ -0,0 +1 @@
+console.log("DONE: foo.jsx");

packages/babel-register/test/fixtures/integration/default-extensions/foo.mjs

@@ -0,0 +1 @@
+console.log("DONE: foo.mjs");

packages/babel-register/test/fixtures/integration/default-extensions/foo.ts

@@ -0,0 +1 @@
+console.log("DONE: foo.ts");

packages/babel-register/test/fixtures/integration/default-extensions/foo.tsx

@@ -0,0 +1 @@
+console.log("DONE: foo.tsx");

packages/babel-register/test/fixtures/integration/default-extensions/index.js

@@ -0,0 +1,11 @@
+require("./foo.jsx");
+require("./foo.es6");
+require("./foo.es");
+require("./foo.mjs");
+
+// Not enabled by default
+require("./foo.ts");
+require("./foo.tsx");
+require("./foo.cjs");
+
+console.log("DONE: index.js");

packages/babel-register/test/fixtures/integration/load-ts/babel.config.json

@@ -0,0 +1,4 @@
+{
+  "extensions": [".js", ".ts"],
+  "plugins": ["../logger"]
+}

packages/babel-register/test/fixtures/integration/load-ts/foo.ts

@@ -0,0 +1 @@
+console.log("DONE: foo.ts");

packages/babel-register/test/fixtures/integration/load-ts/index.js

@@ -0,0 +1,3 @@
+require("./foo.ts");
+
+console.log("DONE: index.js");

packages/babel-register/test/fixtures/integration/logger.js

@@ -0,0 +1,9 @@
+module.exports = function () {
+  return {
+    pre() {
+      console.log(
+        `LOADED: ${JSON.stringify(this.filename.replace(__dirname, "<ROOT>"))}`,
+      );
+    },
+  };
+};

packages/babel-register/test/fixtures/integration/no-load-ts/babel.config.json

@@ -0,0 +1,4 @@
+{
+  "extensions": [".js"],
+  "plugins": ["../logger"]
+}

packages/babel-register/test/fixtures/integration/no-load-ts/foo.ts

@@ -0,0 +1 @@
+console.log("DONE: foo.ts");

packages/babel-register/test/fixtures/integration/no-load-ts/index.js

@@ -0,0 +1,3 @@
+require("./foo.ts");
+
+console.log("DONE: index.js");

packages/babel-register/test/index.js

@@ -37,11 +37,6 @@ jest.mock("source-map-support", () => {
   };
 });
 
-const defaultOptions = {
-  exts: [".js", ".jsx", ".es6", ".es", ".mjs"],
-  ignoreNodeModules: false,
-};
-
 function cleanCache() {
   try {
     fs.unlinkSync(testCacheFilename);
@@ -93,7 +88,8 @@ describe("@babel/register", function () {
     setupRegister();
 
     expect(typeof currentHook).toBe("function");
-    expect(currentOptions).toEqual(defaultOptions);
+    expect(currentOptions.exts).toContain(".js");
+    expect(currentOptions.ignoreNodeModules).toBe(false);
   });
 
   test("unregisters hook correctly", () => {

packages/babel-register/test/integration.js

@@ -0,0 +1,67 @@
+import { exec as execCb } from "child_process";
+
+// TODO(Babel 8): Use util.promisify(execCb)
+const exec = (...args) =>
+  new Promise((resolve, reject) => {
+    execCb(...args, (error, stdout, stderr) => {
+      if (error) reject(error);
+      else resolve({ stdout, stderr });
+    });
+  });
+
+function fixture(name, file = "index.js") {
+  const cwd = `${__dirname}/fixtures/integration/${name}`;
+  return exec(`node -r ${__dirname}/.. ${cwd}/${file}`, {
+    cwd,
+    env: { ...process.env, BABEL_DISABLE_CACHE: true },
+  });
+}
+
+describe("integration tests", function () {
+  it("can hook into extensions defined by the config", async () => {
+    const { stdout, stderr } = await fixture("load-ts");
+
+    expect(stdout).toMatchInlineSnapshot(`
+      "LOADED: \\"<ROOT>/load-ts/index.js\\"
+      LOADED: \\"<ROOT>/load-ts/foo.ts\\"
+      DONE: foo.ts
+      DONE: index.js
+      "
+    `);
+    expect(stderr).toMatchInlineSnapshot(`""`);
+  });
+
+  it("does not hook into unknown extensions", async () => {
+    const { stdout, stderr } = await fixture("no-load-ts");
+
+    expect(stdout).toMatchInlineSnapshot(`
+      "LOADED: \\"<ROOT>/no-load-ts/index.js\\"
+      DONE: foo.ts
+      DONE: index.js
+      "
+    `);
+    expect(stderr).toMatchInlineSnapshot(`""`);
+  });
+
+  it("hooks into the default extensions", async () => {
+    const { stdout, stderr } = await fixture("default-extensions");
+
+    expect(stdout).toMatchInlineSnapshot(`
+      "LOADED: \\"<ROOT>/default-extensions/index.js\\"
+      LOADED: \\"<ROOT>/default-extensions/foo.jsx\\"
+      DONE: foo.jsx
+      LOADED: \\"<ROOT>/default-extensions/foo.es6\\"
+      DONE: foo.es6
+      LOADED: \\"<ROOT>/default-extensions/foo.es\\"
+      DONE: foo.es
+      LOADED: \\"<ROOT>/default-extensions/foo.mjs\\"
+      DONE: foo.mjs
+      DONE: foo.ts
+      DONE: foo.tsx
+      DONE: foo.cjs
+      DONE: index.js
+      "
+    `);
+    expect(stderr).toMatchInlineSnapshot(`""`);
+  });
+});