Multiple assignment case (#23)

Fixes #22.
Tested out with huge bundle in [audio-formant](https://github.com/formant/audio-formant/blob/master/test.js), seems to work ok now.
All tests pass, not sure what other edge cases there can be.

index.js

@@ -186,7 +186,14 @@ function createStream (opts) {
           node.right.type === 'AssignmentExpression' ||
           // Don't output a statement containing only `void () => {}`
           node.right.type === 'ArrowFunctionExpression') {
-        prefix += 'void 0, '
+        // ignore alias assignment expression `exports.a = exports.b = exports.c`
+        if (!(
+          node.right.type === 'AssignmentExpression' &&
+          node.right.left.type === 'MemberExpression' &&
+          node.right.left.object.name === 'exports'
+        )) {
+          prefix += 'void 0, '
+        }
       }
       // Make sure we can't accidentally continue a previous statement.
       // eg in `exports.a = [0]` the `[0]` could continue a previous statement if that

test/funny-exports/expected.js

@@ -11,6 +11,6 @@ console.log(/* common-shake removed: exports.a = */ 'hello world')
 function a() {} /* common-shake removed: exports.b = */ void 0, function () { return a }, console.log(a)
 var c = (0, /* common-shake removed: exports.c = */ 'beep boop')
 
-/* common-shake removed: exports.d = */ void 0, exports.e = null
+/* common-shake removed: exports.d = */ exports.e = null
 
 },{}]},{},[1]);

test/multiple-assign/a.js

@@ -1,5 +1,5 @@
 // This is roughly what Babel's ESM→CommonJS module transform does.
-exports.a = exports.b = null
+exports.a = exports.b = exports.c = exports.d = null
 
 exports.a = 'a'
 exports.b = 'b'

test/multiple-assign/expected.js

@@ -1,6 +1,6 @@
 (function(){function r(e,n,t){function o(i,f){if(!n[i]){if(!e[i]){var c="function"==typeof require&&require;if(!f&&c)return c(i,!0);if(u)return u(i,!0);var a=new Error("Cannot find module '"+i+"'");throw a.code="MODULE_NOT_FOUND",a}var p=n[i]={exports:{}};e[i][0].call(p.exports,function(r){var n=e[i][1][r];return o(n||r)},p,p.exports,r,e,n,t)}return n[i].exports}for(var u="function"==typeof require&&require,i=0;i<t.length;i++)o(t[i]);return o}return r})()({1:[function(require,module,exports){
 // This is roughly what Babel's ESM→CommonJS module transform does.
-exports.a = /* common-shake removed: exports.b = */ null
+exports.a = /* common-shake removed: exports.b = */ /* common-shake removed: exports.c = */ /* common-shake removed: exports.d = */ null
 
 exports.a = 'a'
 /* common-shake removed: exports.b = */ void 'b'

test/test.js

@@ -25,8 +25,8 @@ function runTest (t, name) {
 
   bundle.pipe(concat(function (result) {
     t.is(
-      result.toString('utf8'),
-      fs.readFileSync(expected, 'utf8'),
+      result.toString('utf8').replace(/\r\n/g, '\n'),
+      fs.readFileSync(expected, 'utf8').replace(/\r\n/g, '\n'),
       name
     )
     t.end()