fix: handle deep assignments to `$state()` class properties correctly (#10289)

fixes #10276

.changeset/kind-rings-flash.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: handle deep assignments to `$state()` class properties correctly

packages/svelte/src/compiler/phases/3-transform/client/utils.js

@@ -1,5 +1,10 @@
 import * as b from '../../../utils/builders.js';
-import { extract_paths, is_simple_expression, unwrap_ts_expression } from '../../../utils/ast.js';
+import {
+	extract_paths,
+	is_simple_expression,
+	object,
+	unwrap_ts_expression
+} from '../../../utils/ast.js';
 import { error } from '../../../errors.js';
 import {
 	PROPS_IS_LAZY_INITIAL,
@@ -280,12 +285,13 @@ export function serialize_set_binding(node, context, fallback, options) {
 		error(node, 'INTERNAL', `Unexpected assignment type ${assignee.type}`);
 	}
 
-	let left = assignee;
-
 	// Handle class private/public state assignment cases
-	while (left.type === 'MemberExpression') {
-		if (left.object.type === 'ThisExpression' && left.property.type === 'PrivateIdentifier') {
-			const private_state = context.state.private_state.get(left.property.name);
+	if (assignee.type === 'MemberExpression') {
+		if (
+			assignee.object.type === 'ThisExpression' &&
+			assignee.property.type === 'PrivateIdentifier'
+		) {
+			const private_state = context.state.private_state.get(assignee.property.name);
 			const value = get_assignment_value(node, context);
 			if (private_state !== undefined) {
 				if (state.in_constructor) {
@@ -307,7 +313,7 @@ export function serialize_set_binding(node, context, fallback, options) {
 				} else {
 					return b.call(
 						'$.set',
-						left,
+						assignee,
 						context.state.analysis.runes &&
 							!options?.skip_proxy_and_freeze &&
 							should_proxy_or_freeze(value, context.state.scope)
@@ -319,11 +325,11 @@ export function serialize_set_binding(node, context, fallback, options) {
 				}
 			}
 		} else if (
-			left.object.type === 'ThisExpression' &&
-			left.property.type === 'Identifier' &&
+			assignee.object.type === 'ThisExpression' &&
+			assignee.property.type === 'Identifier' &&
 			state.in_constructor
 		) {
-			const public_state = context.state.public_state.get(left.property.name);
+			const public_state = context.state.public_state.get(assignee.property.name);
 			const value = get_assignment_value(node, context);
 			// See if we should wrap value in $.proxy
 			if (
@@ -342,11 +348,11 @@ export function serialize_set_binding(node, context, fallback, options) {
 				}
 			}
 		}
-		// @ts-expect-error
-		left = unwrap_ts_expression(left.object);
 	}
 
-	if (left.type !== 'Identifier') {
+	const left = object(assignee);
+
+	if (left === null) {
 		return fallback();
 	}
 

packages/svelte/tests/runtime-runes/samples/class-state-deep-update/_config.js

@@ -0,0 +1,15 @@
+import { test } from '../../test';
+
+export default test({
+	html: `<button>0 / 0</button><button>0 / 0</button>`,
+
+	async test({ assert, target }) {
+		const [btn1, btn2] = target.querySelectorAll('button');
+
+		await btn1?.click();
+		assert.htmlEqual(target.innerHTML, `<button>1 / 0</button><button>1 / 0</button>`);
+
+		await btn2?.click();
+		assert.htmlEqual(target.innerHTML, `<button>2 / 1</button><button>2 / 1</button>`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/class-state-deep-update/main.svelte

@@ -0,0 +1,24 @@
+<script>
+	class Counter {
+		container = $state({ count: -1 });
+		#private = $state({ count: -1 });
+
+		constructor(initial_count) {
+			this.container.count = initial_count;
+			this.#private.count = initial_count;
+		}
+
+		increment() {
+			this.container.count += 1;
+			this.#private.count += 1;
+		}
+
+		get private_count() {
+			return this.#private.count;
+		}
+	}
+	const counter = new Counter(0);
+</script>
+
+<button on:click={() => counter.container.count++}>{counter.container.count} / {counter.private_count}</button>
+<button on:click={() => counter.increment()}>{counter.container.count} / {counter.private_count}</button>