handle member expressions in destructuring assignments - fixes #3092

src/compiler/compile/utils/scope.ts

@@ -2,6 +2,7 @@ import { walk } from 'estree-walker';
 import is_reference from 'is-reference';
 import { Node } from '../../interfaces';
 import { Node as ESTreeNode } from 'estree';
+import get_object from './get_object';
 
 export function create_scopes(expression: Node) {
 	const map = new WeakMap();
@@ -114,6 +115,10 @@ const extractors = {
 		nodes.push(param);
 	},
 
+	MemberExpression(nodes: Node[], param: Node) {
+		nodes.push(get_object(param));
+	},
+
 	ObjectPattern(nodes: Node[], param: Node) {
 		param.properties.forEach((prop: Node) => {
 			if (prop.type === 'RestElement') {

test/runtime/samples/destructuring-assignment-array/_config.js

@@ -0,0 +1,23 @@
+export default {
+	html: `
+		<ul>
+			<li>Gruyere</li>
+			<li>Compté</li>
+			<li>Beaufort</li>
+			<li>Abondance</li>
+		</ul>
+	`,
+
+	async test({ assert, component, target }) {
+		await component.swap(0, 1);
+
+		assert.htmlEqual(target.innerHTML, `
+			<ul>
+				<li>Compté</li>
+				<li>Gruyere</li>
+				<li>Beaufort</li>
+				<li>Abondance</li>
+			</ul>
+		`);
+	}
+};

test/runtime/samples/destructuring-assignment-array/main.svelte

@@ -0,0 +1,18 @@
+<script>
+	let cheese = [
+		'Gruyere',
+		'Compté',
+		'Beaufort',
+		'Abondance',
+	];
+
+	export function swap(a, b) {
+		[cheese[a], cheese[b]] = [cheese[b], cheese[a]];
+	}
+</script>
+
+<ul>
+	{#each cheese as cheese}
+		<li>{cheese}</li>
+	{/each}
+</ul>