Prevent invalid code when removing assignment target of side-effectfu…

…l object expression (#3921)

src/ast/nodes/AssignmentExpression.ts

@@ -1,7 +1,9 @@
 import MagicString from 'magic-string';
+import { BLANK } from '../../utils/blank';
 import {
 	findFirstOccurrenceOutsideComment,
 	findNonWhiteSpace,
+	NodeRenderOptions,
 	RenderOptions
 } from '../../utils/renderHelpers';
 import { getSystemExportFunctionLeft } from '../../utils/systemJsRendering';
@@ -62,11 +64,18 @@ export default class AssignmentExpression extends NodeBase {
 		this.right.include(context, includeChildrenRecursively);
 	}
 
-	render(code: MagicString, options: RenderOptions) {
-		this.right.render(code, options);
+	render(
+		code: MagicString,
+		options: RenderOptions,
+		{ renderedParentType }: NodeRenderOptions = BLANK
+	) {
 		if (this.left.included) {
 			this.left.render(code, options);
+			this.right.render(code, options);
 		} else {
+			this.right.render(code, options, {
+				renderedParentType: renderedParentType || this.parent.type
+			});
 			code.remove(this.start, this.right.start);
 		}
 		if (options.format === 'system') {

test/function/samples/tree-shake-object-expression-assignment/_config.js

@@ -0,0 +1,4 @@
+module.exports = {
+	description:
+		'renders valid code when the target of an object expression with side-effects is tree-shaken'
+};

test/function/samples/tree-shake-object-expression-assignment/main.js

@@ -0,0 +1,6 @@
+const result = {};
+
+let foo;
+foo = { [(result.x = 1)]: (result.y = 2) };
+
+assert.deepStrictEqual(result, { x: 1, y: 2 });