Treeshake functions properly (#2418)

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

@@ -0,0 +1,2 @@
+import {add} from './b';
+export default add(4, 5);

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

@@ -0,0 +1,7 @@
+export function add(a, b) {
+	return a + b;
+}
+
+export function sub(a, b) {
+	return a - b;
+}

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

@@ -433,6 +433,26 @@ describe('scope hoisting', function() {
       assert(!contents.includes('bar'));
     });
 
+    it('removes unused function exports when minified', async function() {
+      let b = await bundle(
+        path.join(
+          __dirname,
+          '/integration/scope-hoisting/es6/tree-shaking-functions/a.js'
+        ),
+        {minify: true}
+      );
+
+      let output = await run(b);
+      assert.deepEqual(output.default, 9);
+
+      let contents = await fs.readFile(
+        path.join(__dirname, '/dist/a.js'),
+        'utf8'
+      );
+      assert(/.\+./.test(contents));
+      assert(!/.-./.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

@@ -104,7 +104,13 @@ function isUnusedWildcard(path) {
 
 function remove(path) {
   if (path.isAssignmentExpression()) {
-    if (!path.parentPath.isExpressionStatement()) {
+    if (path.parentPath.isSequenceExpression()) {
+      if (path.parent.expressions.length == 1) {
+        path.parentPath.remove();
+      } else {
+        path.remove();
+      }
+    } else if (!path.parentPath.isExpressionStatement()) {
       path.replaceWith(path.node.right);
     } else {
       path.remove();
@@ -113,11 +119,6 @@ function remove(path) {
     remove(path.parentPath.parentPath);
   } else if (isUnusedWildcard(path)) {
     remove(path.parentPath);
-  } else if (
-    path.parentPath.isSequenceExpression() &&
-    path.parent.expressions.length === 1
-  ) {
-    remove(path.parentPath);
   } else if (!path.removed) {
     path.remove();
   }