widen ownership if assigning different state proxies to one another

Author: dummdidumm

packages/svelte/src/internal/client/dev/ownership.js

@@ -125,6 +125,27 @@ export function add_owner(object, owner, global = false) {
 	add_owner_to_object(object, owner);
 }
 
+/**
+ * @param {import('#client').ProxyMetadata | null} from
+ * @param {import('#client').ProxyMetadata} to
+ */
+export function widen_ownership(from, to) {
+	if (to.owners === null) {
+		return;
+	}
+
+	while (from) {
+		if (from.owners === null) {
+			to.owners = null;
+			break;
+		}
+		for (const owner of from.owners) {
+			to.owners.add(owner);
+		}
+		from = from.parent;
+	}
+}
+
 /**
  * @param {any} object
  * @param {Function} owner

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

@@ -16,7 +16,7 @@ import {
 	is_frozen,
 	object_prototype
 } from './utils.js';
-import { check_ownership } from './dev/ownership.js';
+import { check_ownership, widen_ownership } from './dev/ownership.js';
 import { mutable_source, source, set } from './reactivity/sources.js';
 import { STATE_SYMBOL } from './constants.js';
 import { UNINITIALIZED } from '../../constants.js';
@@ -280,6 +280,11 @@ const state_proxy_handler = {
 		const not_has = !(prop in target);
 
 		if (DEV) {
+			/** @type {import('#client').ProxyMetadata | undefined} */
+			const prop_metadata = value?.[STATE_SYMBOL];
+			if (prop_metadata && prop_metadata?.parent !== metadata) {
+				widen_ownership(metadata, prop_metadata);
+			}
 			check_ownership(metadata);
 		}
 

packages/svelte/tests/runtime-runes/samples/non-local-mutation-inherited-owner/main.svelte

@@ -2,7 +2,8 @@
 	import Counter from './Counter.svelte';
 	import { global } from './state.svelte.js';
 
-	global.object = { count: 0 };
+	let object = $state({ count: 0 });
+	global.object = object;
 </script>
 
 <Counter />