Make treeshaking handle "multiassignments" (#2729)

packages/core/integration-tests/test/integration/scope-hoisting/es6/tree-shaking-multiassignment/a.js

@@ -0,0 +1,2 @@
+import x, {y} from "./b";
+export default [x, y];

packages/core/integration-tests/test/integration/scope-hoisting/es6/tree-shaking-multiassignment/b.js

@@ -0,0 +1,9 @@
+exports.default = exports.y = exports.z = undefined;
+var y = 'y';
+exports.y = y;
+var z = 'z';
+exports.z = z;
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});

packages/core/integration-tests/test/scope-hoisting.js

@@ -485,6 +485,25 @@ describe('scope hoisting', function() {
       assert(!/.-./.test(contents));
     });
 
+    it('handle export multi-assignment', async function() {
+      let b = await bundle(
+        path.join(
+          __dirname,
+          '/integration/scope-hoisting/es6/tree-shaking-multiassignment/a.js'
+        ),
+        {minify: true}
+      );
+
+      let output = await run(b);
+      assert.deepEqual(output.default, [undefined, 'y']);
+
+      // let contents = await fs.readFile(
+      //   path.join(__dirname, '/dist/a.js'),
+      //   'utf8'
+      // );
+      // assert(!/["']z["']/.test(contents));
+    });
+
     it('support exporting a ES6 module exported as CommonJS', async function() {
       let b = await bundle(
         path.join(

packages/core/parcel-bundler/src/scope-hoisting/shake.js

@@ -106,7 +106,9 @@ function remove(path) {
   if (path.isAssignmentExpression()) {
     if (path.parentPath.isSequenceExpression()) {
       if (path.parent.expressions.length == 1) {
-        path.parentPath.remove();
+        // replace sequence expression with it's sole child
+        path.parentPath.replaceWith(path);
+        remove(path.parentPath);
       } else {
         path.remove();
       }