From d8c37fd9fcb5b2c01f738bd508e3183e148fdf2e Mon Sep 17 00:00:00 2001
From: Frankie Dintino <fdintino@gmail.com>
Date: Thu, 23 Aug 2018 02:56:01 -0400
Subject: [PATCH] Use terser to support minification of more permissive babel
 presets

Currently, only ES5 javascript can be minified, due to the reliance on
uglify-js. With terser (a maintained fork of the harmony branch of
UglifyJS2) it is possible to support a broader range of javascript
syntax.

The API changed between uglify-js@2 and uglify-js@3 / terser, but the
translation to the new API was fairly straightforward. It hews more
closely to the original code than #815, and consequently I think it
avoids regressing any features (for instance, the ability to include
sourceContents in source maps or to control the comment stripping is
retained).

As browsers continue to support more features beyond ES5, and
because babel recommends use of the 'env' preset, it will become
increasingly likely that users' babel transpilation settings will cause
errors when trying to minify with jspm and friends as long as it uses
uglify-js.

refs #815, #726
---
 lib/output.js      | 39 ++++++++++++++++++++++-----------------
 package.json       |  4 ++--
 test/test-sfx.html |  3 +--
 3 files changed, 25 insertions(+), 21 deletions(-)

diff --git a/lib/output.js b/lib/output.js
index 777ee3e..e45d050 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -8,6 +8,17 @@ var extend = require('./utils').extend;
 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', 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'));
+
 function countLines(str) {
   return str.split(/\r\n|\r|\n/).length;
 }
@@ -72,36 +83,30 @@ function createOutput(outFile, outputs, basePath, sourceMaps, sourceMapContents)
 }
 
 function minify(output, fileName, mangle, uglifyOpts) {
-  var uglify = require('uglify-js');
+  var terser = require('terser');
+  var files = {};
+  files[fileName] = output.source;
   var ast;
   try{
-    ast = uglify.parse(output.source, { filename: fileName });
+    ast = terser.minify(files, {
+      parse: {},
+      compress: false,
+      mangle: mangle,
+      output: { ast: true, code: false }
+    }).ast;
   } 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();
 
   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;
diff --git a/package.json b/package.json
index 14e7360..78142a4 100644
--- a/package.json
+++ b/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",
diff --git a/test/test-sfx.html b/test/test-sfx.html
index 36f4f84..2374570 100644
--- a/test/test-sfx.html
+++ b/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');