Add --keep-file-extension option to babel-cli (#6221)

* Add --keep-module-extension option to babel-cli

* Rename keep-module-extension option to keep-file-extension; Change option to preserve all file extensions

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

@@ -13,7 +13,7 @@ export default function(commander, filenames, opts) {
     }
 
     // remove extension and then append back on .js
-    relative = relative.replace(/\.(\w*?)$/, "") + ".js";
+    relative = util.adjustRelative(relative, commander.keepFileExtension);
 
     const dest = getDest(commander, relative, base);
 

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

@@ -129,6 +129,10 @@ commander.option(
   "List of extensions to compile when a directory has been input [.es6,.js,.es,.jsx,.mjs]",
   collect,
 );
+commander.option(
+  "--keep-file-extension",
+  "Preserve the file extensions of the input files",
+);
 commander.option("-w, --watch", "Recompile files on changes");
 commander.option(
   "--skip-initial-build",
@@ -232,6 +236,7 @@ delete opts.copyFiles;
 delete opts.quiet;
 delete opts.configFile;
 delete opts.deleteDirOnStart;
+delete opts.keepFileExtension;
 
 // Commander will default the "--no-" arguments to true, but we want to leave them undefined so that
 // babel-core can handle the default-assignment logic on its own.

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

@@ -98,3 +98,10 @@ export function requireChokidar() {
     throw err;
   }
 }
+
+export function adjustRelative(relative, keepFileExtension) {
+  if (keepFileExtension) {
+    return relative;
+  }
+  return relative.replace(/\.(\w*?)$/, "") + ".js";
+}