fix: enable bound store props in runes mode components (#13887)

* fix: enable bound store props in runes mode components

* add some JSDoc, since it could be a headscratcher for future us

* make it clear that this is specifically about bindings

* skip intermediate value

* tweak other names too

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

.changeset/cool-clocks-march.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: enable bound store props in runes mode components

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js

@@ -188,7 +188,17 @@ export function build_component(node, component_name, context, anchor = context.
 					);
 				}
 
-				push_prop(b.get(attribute.name, [b.return(expression)]));
+				const is_store_sub =
+					attribute.expression.type === 'Identifier' &&
+					context.state.scope.get(attribute.expression.name)?.kind === 'store_sub';
+
+				if (is_store_sub) {
+					push_prop(
+						b.get(attribute.name, [b.stmt(b.call('$.mark_store_binding')), b.return(expression)])
+					);
+				} else {
+					push_prop(b.get(attribute.name, [b.return(expression)]));
+				}
 
 				const assignment = b.assignment('=', attribute.expression, b.id('$$value'));
 				push_prop(

packages/svelte/src/internal/client/index.js

@@ -121,7 +121,8 @@ export {
 	store_set,
 	store_unsub,
 	update_pre_store,
-	update_store
+	update_store,
+	mark_store_binding
 } from './reactivity/store.js';
 export { set_text } from './render.js';
 export {

packages/svelte/src/internal/client/reactivity/props.js

@@ -23,6 +23,7 @@ import { safe_equals } from './equality.js';
 import * as e from '../errors.js';
 import { BRANCH_EFFECT, DESTROYED, LEGACY_DERIVED_PROP, ROOT_EFFECT } from '../constants.js';
 import { proxy } from '../proxy.js';
+import { capture_store_binding } from './store.js';
 
 /**
  * @param {((value?: number) => number)} fn
@@ -273,8 +274,14 @@ export function prop(props, key, flags, fallback) {
 	var runes = (flags & PROPS_IS_RUNES) !== 0;
 	var bindable = (flags & PROPS_IS_BINDABLE) !== 0;
 	var lazy = (flags & PROPS_IS_LAZY_INITIAL) !== 0;
+	var is_store_sub = false;
+	var prop_value;
 
-	var prop_value = /** @type {V} */ (props[key]);
+	if (bindable) {
+		[prop_value, is_store_sub] = capture_store_binding(() => /** @type {V} */ (props[key]));
+	} else {
+		prop_value = /** @type {V} */ (props[key]);
+	}
 	var setter = get_descriptor(props, key)?.set;
 
 	var fallback_value = /** @type {V} */ (fallback);
@@ -343,7 +350,7 @@ export function prop(props, key, flags, fallback) {
 				// In that case the state proxy (if it exists) should take care of the notification.
 				// If the parent is not in runes mode, we need to notify on mutation, too, that the prop
 				// has changed because the parent will not be able to detect the change otherwise.
-				if (!runes || !mutation || legacy_parent) {
+				if (!runes || !mutation || legacy_parent || is_store_sub) {
 					/** @type {Function} */ (setter)(mutation ? getter() : value);
 				}
 				return value;

packages/svelte/src/internal/client/reactivity/store.js

@@ -6,6 +6,13 @@ import { get } from '../runtime.js';
 import { teardown } from './effects.js';
 import { mutable_source, set } from './sources.js';
 
+/**
+ * Whether or not the prop currently being read is a store binding, as in
+ * `<Child bind:x={$y} />`. If it is, we treat the prop as mutable even in
+ * runes mode, and skip `binding_property_non_reactive` validation
+ */
+let is_store_binding = false;
+
 /**
  * Gets the current value of a store. If the store isn't subscribed to yet, it will create a proxy
  * signal that will be updated when the store is. The store references container is needed to
@@ -146,3 +153,29 @@ export function update_pre_store(store, store_value, d = 1) {
 	store.set(value);
 	return value;
 }
+
+/**
+ * Called inside prop getters to communicate that the prop is a store binding
+ */
+export function mark_store_binding() {
+	is_store_binding = true;
+}
+
+/**
+ * Returns a tuple that indicates whether `fn()` reads a prop that is a store binding.
+ * Used to prevent `binding_property_non_reactive` validation false positives and
+ * ensure that these props are treated as mutable even in runes mode
+ * @template T
+ * @param {() => T} fn
+ * @returns {[T, boolean]}
+ */
+export function capture_store_binding(fn) {
+	var previous_is_store_binding = is_store_binding;
+
+	try {
+		is_store_binding = false;
+		return [fn(), is_store_binding];
+	} finally {
+		is_store_binding = previous_is_store_binding;
+	}
+}

packages/svelte/src/internal/client/validate.js

@@ -4,6 +4,7 @@ import * as e from './errors.js';
 import { FILENAME } from '../../constants.js';
 import { render_effect } from './reactivity/effects.js';
 import * as w from './warnings.js';
+import { capture_store_binding } from './reactivity/store.js';
 
 /** regex of all html void element names */
 const void_element_names =
@@ -84,7 +85,10 @@ export function validate_binding(binding, get_object, get_property, line, column
 	render_effect(() => {
 		if (warned) return;
 
-		var object = get_object();
+		var [object, is_store_sub] = capture_store_binding(get_object);
+
+		if (is_store_sub) return;
+
 		var property = get_property();
 
 		var ran = false;

packages/svelte/tests/runtime-runes/samples/bound-store-sub/Child.svelte

@@ -0,0 +1,7 @@
+<script>
+	let { form = $bindable() } = $props();
+</script>
+
+<p>
+	<input type="number" bind:value={form.count} />
+</p>

packages/svelte/tests/runtime-runes/samples/bound-store-sub/_config.js

@@ -0,0 +1,25 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+import { ok } from 'assert';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+
+	html: `<p><input type="number"></p>\n{"count":0}`,
+	ssrHtml: `<p><input type="number" value="0"></p>\n{"count":0}`,
+
+	test({ assert, target }) {
+		const input = target.querySelector('input');
+		ok(input);
+		const inputEvent = new window.InputEvent('input');
+
+		input.value = '10';
+		input.dispatchEvent(inputEvent);
+
+		flushSync();
+
+		assert.htmlEqual(target.innerHTML, `<p><input type="number"></p>\n{"count":10}`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/bound-store-sub/main.svelte

@@ -0,0 +1,11 @@
+<script>
+	import { writable } from 'svelte/store';
+	import Child from './Child.svelte';
+
+	let form = writable({
+		count: 0
+	});
+</script>
+
+<Child bind:form={$form} />
+{JSON.stringify($form)}