use acorn-globals to avoid collisions with implied globals (#1079)

package.json

@@ -47,6 +47,7 @@
     "@types/node": "^8.0.17",
     "acorn": "^5.1.1",
     "acorn-dynamic-import": "^2.0.2",
+    "acorn-globals": "^4.1.0",
     "chalk": "^2.0.1",
     "codecov": "^2.2.0",
     "console-group": "^0.3.2",

src/generators/Generator.ts

@@ -1,6 +1,7 @@
 import MagicString, { Bundle } from 'magic-string';
 import { walk, childKeys } from 'estree-walker';
 import { getLocator } from 'locate-character';
+import detectGlobals from 'acorn-globals';
 import deindent from '../utils/deindent';
 import CodeBuilder from '../utils/CodeBuilder';
 import getCodeFrame from '../utils/getCodeFrame';
@@ -414,6 +415,9 @@ export default class Generator {
 			scope.declarations.forEach(name => {
 				this.userVars.add(name);
 			});
+			detectGlobals(js.content).forEach(({ name }) => {
+				this.userVars.add(name);
+			});
 
 			const body = js.content.body.slice(); // slice, because we're going to be mutating the original
 

yarn.lock

@@ -28,7 +28,7 @@ acorn-dynamic-import@^2.0.2:
   dependencies:
     acorn "^4.0.3"
 
-acorn-globals@^4.0.0:
+acorn-globals@^4.0.0, acorn-globals@^4.1.0:
   version "4.1.0"
   resolved "https://registry.yarnpkg.com/acorn-globals/-/acorn-globals-4.1.0.tgz#ab716025dbe17c54d3ef81d32ece2b2d99fe2538"
   dependencies: