fix: access last safe value of prop on unmount

Author: trueadm

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

@@ -14,6 +14,7 @@ import {
 import { effect, teardown } from './reactivity/effects.js';
 import { legacy_mode_flag } from '../flags/index.js';
 import { CTX_CONTAINS_TEARDOWN, CTX_DESTROYED } from './constants.js';
+import { define_property } from '../shared/utils.js';
 
 /** @type {ComponentContext | null} */
 export let component_context = null;
@@ -145,7 +146,7 @@ export function push(props, runes = false, fn) {
 		var teardown_props = ctx.tp;
 		// Apply the latest known props before teardown over existing props
 		for (var key in teardown_props) {
-			Object.defineProperty(props, key, {
+			define_property(props, key, {
 				value: teardown_props[key],
 				configurable: true
 			});

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

@@ -7,7 +7,7 @@ import {
 	PROPS_IS_RUNES,
 	PROPS_IS_UPDATED
 } from '../../../constants.js';
-import { get_descriptor, is_function } from '../../shared/utils.js';
+import { define_property, get_descriptor, is_function } from '../../shared/utils.js';
 import { mutable_source, set, source, update } from './sources.js';
 import { derived, derived_safe_equal } from './deriveds.js';
 import {
@@ -201,6 +201,18 @@ const spread_props_handler = {
 		}
 		return false;
 	},
+	defineProperty(target, key, descriptor) {
+		let i = target.props.length;
+		while (i--) {
+			let p = target.props[i];
+			if (is_function(p)) p = p();
+			if (typeof p === 'object' && p !== null && key in p) {
+				define_property(p, key, descriptor);
+				return true;
+			}
+		}
+		return false;
+	},
 	getOwnPropertyDescriptor(target, key) {
 		let i = target.props.length;
 		while (i--) {

packages/svelte/tests/runtime-runes/samples/ondestroy-prop-access/_config.js

@@ -61,8 +61,8 @@ export default test({
 			true,
 			2,
 			true,
-			2,
-			false
+			1,
+			true
 		]);
 	}
 });