Add --use-file-extension option to babel-cli

packages/babel-cli/src/babel/dir.js

@@ -17,8 +17,12 @@ export default async function({ cliOptions, babelOptions }) {
       return false;
     }
 
-    // remove extension and then append back on .js
-    relative = util.adjustRelative(relative, cliOptions.keepFileExtension);
+    // remove extension and then append back on the configured extension
+    relative = util.adjustRelative(
+      relative,
+      cliOptions.keepFileExtension,
+      cliOptions.useFileExtension,
+    );
 
     const dest = getDest(relative, base);
 

packages/babel-cli/src/babel/options.js

@@ -147,6 +147,10 @@ commander.option(
   "--delete-dir-on-start",
   "Delete the out directory before compilation",
 );
+commander.option(
+  "--use-file-extension [string]",
+  "Use a specific extension for the output files",
+);
 
 commander.version(pkg.version + " (@babel/core " + version + ")");
 commander.usage("[options] <files ...>");
@@ -267,6 +271,7 @@ export default function parseArgv(args: Array<string>) {
       filenames,
       extensions: opts.extensions,
       keepFileExtension: opts.keepFileExtension,
+      useFileExtension: opts.useFileExtension,
       watch: opts.watch,
       skipInitialBuild: opts.skipInitialBuild,
       outFile: opts.outFile,

packages/babel-cli/src/babel/util.js

@@ -118,9 +118,9 @@ export function requireChokidar() {
   }
 }
 
-export function adjustRelative(relative, keepFileExtension) {
+export function adjustRelative(relative, keepFileExtension, extension = ".js") {
   if (keepFileExtension) {
     return relative;
   }
-  return relative.replace(/\.(\w*?)$/, "") + ".js";
+  return relative.replace(/\.(\w*?)$/, "") + extension;
 }

packages/babel-cli/test/fixtures/babel/dir --out-dir --use-file-extension/in-files/src/bar.mjs

@@ -0,0 +1 @@
+arr.map(x => x / DIVIDER);

packages/babel-cli/test/fixtures/babel/dir --out-dir --use-file-extension/in-files/src/foo.jsx

@@ -0,0 +1 @@
+arr.map(x => x * MULTIPLIER);

packages/babel-cli/test/fixtures/babel/dir --out-dir --use-file-extension/options.json

@@ -0,0 +1,12 @@
+{
+  "args": [
+    "src",
+    "--out-dir",
+    "lib",
+    "--use-file-extension",
+    ".mjs",
+    "--extensions",
+    ".jsx,.mjs",
+    "--verbose"
+  ]
+}

packages/babel-cli/test/fixtures/babel/dir --out-dir --use-file-extension/out-files/lib/bar.mjs

@@ -0,0 +1,5 @@
+"use strict";
+
+arr.map(function (x) {
+  return x / DIVIDER;
+});

packages/babel-cli/test/fixtures/babel/dir --out-dir --use-file-extension/out-files/lib/foo.mjs

@@ -0,0 +1,5 @@
+"use strict";
+
+arr.map(function (x) {
+  return x * MULTIPLIER;
+});

packages/babel-cli/test/fixtures/babel/dir --out-dir --use-file-extension/stdout.txt

@@ -0,0 +1,3 @@
+src/bar.mjs -> lib/bar.mjs
+src/foo.jsx -> lib/foo.mjs
+Successfully compiled 2 files with Babel.