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

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

@@ -23,8 +23,12 @@ export default async function({
       return false;
     }
 
-    // remove extension and then append back on .js
-    relative = util.adjustRelative(relative, cliOptions.keepFileExtension);
+    relative = util.withExtension(
+      relative,
+      cliOptions.keepFileExtension
+        ? path.extname(relative)
+        : cliOptions.outFileExtension,
+    );
 
     const dest = getDest(relative, base);
 

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

@@ -149,6 +149,10 @@ commander.option(
   "--delete-dir-on-start",
   "Delete the out directory before compilation",
 );
+commander.option(
+  "--out-file-extension [string]",
+  "Use a specific extension for the output files",
+);
 
 commander.version(pkg.version + " (@babel/core " + version + ")");
 commander.usage("[options] <files ...>");
@@ -218,6 +222,12 @@ export default function parseArgv(args: Array<string>): CmdOptions {
     );
   }
 
+  if (commander.keepFileExtension && commander.outFileExtension) {
+    errors.push(
+      "--out-file-extension cannot be used with --keep-file-extension",
+    );
+  }
+
   if (errors.length) {
     console.error("babel:");
     errors.forEach(function(e) {
@@ -274,6 +284,7 @@ export default function parseArgv(args: Array<string>): CmdOptions {
       filenames,
       extensions: opts.extensions,
       keepFileExtension: opts.keepFileExtension,
+      outFileExtension: opts.outFileExtension,
       watch: opts.watch,
       skipInitialBuild: opts.skipInitialBuild,
       outFile: opts.outFile,

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

@@ -127,12 +127,7 @@ export function requireChokidar(): Object {
   }
 }
 
-export function adjustRelative(
-  relative: string,
-  keepFileExtension: boolean,
-): string {
-  if (keepFileExtension) {
-    return relative;
-  }
-  return relative.replace(/\.(\w*?)$/, "") + ".js";
+export function withExtension(filename: string, ext: string = ".js") {
+  const newBasename = path.basename(filename, path.extname(filename)) + ext;
+  return path.join(path.dirname(filename), newBasename);
 }

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

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

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

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

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

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

packages/babel-cli/test/fixtures/babel/dir --out-dir --out-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 --out-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 --out-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.

packages/babel-cli/test/fixtures/babel/error --keep-file-extension --out-file-extension/options.json

@@ -0,0 +1,4 @@
+{
+  "args": ["--keep-file-extension", "--out-file-extension", ".mjs"],
+  "stderrContains": true
+}

packages/babel-cli/test/fixtures/babel/error --keep-file-extension --out-file-extension/stderr.txt

@@ -0,0 +1 @@
+--out-file-extension cannot be used with --keep-file-extension