Use terser (uglify-js fork) to support minification of more permissive babel presets

lib/output.js

@@ -4,10 +4,22 @@ var fs = require('fs');
 var Promise = require('bluebird');
 var asp = require('bluebird').promisify;
 var extend = require('./utils').extend;
+var terser = require('terser');
 
 var fromFileURL = require('./utils').fromFileURL;
 var toFileURL = require('./utils').toFileURL;
 
+// Ugly hack to get around terser's strange code loading and export system
+// (inherited from uglify-js), and the fact that their SourceMap wrapper is
+// not exported
+var TerserSourceMap = new Function('MOZ_SourceMap', "exports", "require", function() {
+  var code = ['terser/lib/utils.js', 'terser/lib/sourcemap.js'].map(function(file) {
+    return fs.readFileSync(require.resolve(file), 'utf8');
+  });
+  code.push('return SourceMap;');
+  return code.join('\n');
+}())(require('source-map'), terser, require);
+
 function countLines(str) {
   return str.split(/\r\n|\r|\n/).length;
 }
@@ -72,36 +84,35 @@ function createOutput(outFile, outputs, basePath, sourceMaps, sourceMapContents)
 }
 
 function minify(output, fileName, mangle, uglifyOpts) {
-  var uglify = require('uglify-js');
-  var ast;
+  var files = {};
+  files[fileName] = output.source;
+  var result;
   try{
-    ast = uglify.parse(output.source, { filename: fileName });
+    result = terser.minify(files, {
+      parse: {},
+      compress: uglifyOpts.compress,
+      mangle: mangle,
+      output: { ast: true, code: false }
+    });
   } catch(e){
     throw new Error(e);
   }
-  ast.figure_out_scope();
-
-  ast = ast.transform(uglify.Compressor(uglifyOpts.compress));
-  ast.figure_out_scope();
-  if (mangle !== false)
-    ast.mangle_names();
+
+  if (result.error) {
+    throw new Error(result.error);
+  }
+
+  var ast = result.ast;
 
   var sourceMap;
   if (output.sourceMap) {
     if (typeof output.sourceMap === 'string')
       output.sourceMap = JSON.parse(output.sourceMap);
 
-    var sourceMapIn = output.sourceMap;
-    sourceMap = uglify.SourceMap({
+    sourceMap = TerserSourceMap({
       file: fileName,
-      orig: sourceMapIn
+      orig: output.sourceMap
     });
-
-    if (uglifyOpts.sourceMapIncludeSources && sourceMapIn && Array.isArray(sourceMapIn.sourcesContent)) {
-      sourceMapIn.sourcesContent.forEach(function(content, idx) {
-        sourceMap.get().setSourceContent(sourceMapIn.sources[idx], content);
-      });
-    }
   }
 
   var outputOptions = uglifyOpts.beautify;

package.json

@@ -19,8 +19,8 @@
     "rollup": "^0.58.2",
     "source-map": "^0.5.3",
     "systemjs": "^0.19.46",
-    "traceur": "0.0.105",
-    "uglify-js": "^2.6.1"
+    "terser": "^3.8.1",
+    "traceur": "0.0.105"
   },
   "devDependencies": {
     "babel": "^5.8.38",

test/arithmetic.js

@@ -37,7 +37,7 @@ suite('Bundle Expressions', function() {
     .then(function(tree) {
       assert.deepEqual(Object.keys(tree).sort(), [
           'Buffer.js', 'amd.js', 'babel', 'babel.js', 'cjs space.js', 'cjs-1.js', 'cjs-2.js', 'cjs-3.js', 'cjs-4.js', 'cjs-5.js', 'cjs-globals.js', 'cjs-in-12.js', 'cjs-in-13.js',
-          'cjs-resolve.js', 'cjs.js', 'component.jsx!jsx.js', 'example.js', 'file.json', 'first.js',
+          'cjs-resolve.js', 'cjs.js', 'class-def.js', 'component.jsx!jsx.js', 'example.js', 'file.json', 'first.js',
           'global-inner.js', 'global-outer.js', 'global.js', 'jquery-cdn', 'jquery.js', 'json-plugin.js', 'jsx.js', 'plugin.js', 'register.js', 'runtime.js', 
           'second.js', 'some.js!plugin.js', 'text-plugin.js', 'text.txt!text-plugin.js', 'third.js', 'umd.js']);
     })

test/fixtures/test-tree/class-def.js

@@ -0,0 +1,13 @@
+class Foo {
+  constructor() {
+    this.bar = 'bar';
+  }
+  static get baz() { return 'baz'; }
+}
+
+const foo = new Foo();
+
+module.exports = {
+  foo: foo,
+  barbaz: `${foo.bar}${Foo.baz}`,
+};

test/test-build.js

@@ -243,3 +243,21 @@ suite('Bundle Format', function() {
     });
   });
 });
+
+suite('Test ES6 minification', function() {
+  test('ES6 syntax minify, unmangled', function() {
+    builder.reset();
+    return builder.bundle('class-def.js', { minify: true , mangle: false })
+    .then(function(output) {
+      assert.match(output.source, /class Foo{constructor\(\){/, 'source contains literal class');
+    });
+  });
+
+  test('ES6 syntax minify, mangled', function() {
+    builder.reset();
+    return builder.bundle('class-def.js', { minify: true , mangle: true })
+    .then(function(output) {
+      assert.match(output.source, /class \w{constructor\(\){/, 'source contains literal class, mangled');
+    });
+  });
+});

test/test-sfx.html

@@ -6,13 +6,12 @@
     <div id="mocha">
   <script>
     window.$ = { jquery: 1 };
+    window.DEBUG = false;
   </script>
   <script src="output/sfx.js"></script>
   <script>
     mocha.setup('tdd');
 
-    DEBUG = false;
-
     function assert(assertion, msg) {
       if (!assertion)
         throw new Error(msg || 'Assertion failed');