fix: ensure class constructor values are proxied

.changeset/tall-books-grin.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure class constructor values are proxied

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

@@ -157,16 +157,45 @@ export function serialize_set_binding(node, context, fallback) {
 
 	let left = node.left;
 
+	// Handle class private/public state assignment cases
 	while (left.type === 'MemberExpression') {
-		if (left.object.type === 'ThisExpression' && left.property.type === 'PrivateIdentifier') {
-			if (context.state.private_state.has(left.property.name) && !state.in_constructor) {
-				const value = get_assignment_value(node, context);
+		if (
+			left.object.type === 'ThisExpression' &&
+			left.property.type === 'PrivateIdentifier' &&
+			context.state.private_state.has(left.property.name)
+		) {
+			const value = get_assignment_value(node, context);
+			if (state.in_constructor) {
+				// See if we should wrap value in $.proxy
+				if (context.state.analysis.runes && should_proxy(value)) {
+					const assignment = fallback();
+					if (assignment.type === 'AssignmentExpression') {
+						assignment.right = b.call('$.proxy', value);
+						return assignment;
+					}
+				}
+			} else {
 				return b.call(
 					'$.set',
 					left,
 					context.state.analysis.runes && should_proxy(value) ? b.call('$.proxy', value) : value
 				);
 			}
+		} else if (
+			left.object.type === 'ThisExpression' &&
+			left.property.type === 'Identifier' &&
+			context.state.public_state.has(left.property.name) &&
+			state.in_constructor
+		) {
+			const value = get_assignment_value(node, context);
+			// See if we should wrap value in $.proxy
+			if (context.state.analysis.runes && should_proxy(value)) {
+				const assignment = fallback();
+				if (assignment.type === 'AssignmentExpression') {
+					assignment.right = b.call('$.proxy', value);
+					return assignment;
+				}
+			}
 		}
 		// @ts-expect-error
 		left = left.object;

packages/svelte/tests/runtime-runes/samples/class-private-state-proxy/_config.js

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

packages/svelte/tests/runtime-runes/samples/class-private-state-proxy/main.svelte

@@ -0,0 +1,16 @@
+<script>
+	class Counter {
+		#count = $state();
+
+		constructor(v) {
+			this.#count = v;
+		}
+
+		get count() {
+			return this.#count;
+		}
+	}
+	const counter = new Counter({ count: 0 });
+</script>
+
+<button on:click={() => counter.count.count++}>{counter.count.count}</button>

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

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

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

@@ -0,0 +1,12 @@
+<script>
+	class Counter {
+		count = $state();
+
+		constructor(v) {
+			this.count = v;
+		}
+	}
+	const counter = new Counter({ count: 0 });
+</script>
+
+<button on:click={() => counter.count.count++}>{counter.count.count}</button>