fix $$props reactivity in fallback of a slot (#5375)

CHANGELOG.md

@@ -11,6 +11,7 @@
 * Fix using `<svelte:component>` in `{:catch}` ([#5259](https://github.com/sveltejs/svelte/issues/5259))
 * Fix setting one-way bound `<input>` `value` to `undefined` when it has spread attributes ([#5270](https://github.com/sveltejs/svelte/issues/5270))
 * Fix deep two-way bindings inside an `{#each}` involving a store ([#5286](https://github.com/sveltejs/svelte/issues/5286))
+* Fix reactivity of `$$props` in slot fallback content ([#5367](https://github.com/sveltejs/svelte/issues/5367))
 
 ## 3.24.1
 

src/compiler/compile/render_dom/wrappers/shared/is_dynamic.ts

@@ -1,9 +1,11 @@
 import { Var } from '../../../../interfaces';
+import { is_reserved_keyword } from '../../../utils/reserved_keywords';
 
 export default function is_dynamic(variable: Var) {
 	if (variable) {
 		if (variable.mutated || variable.reassigned) return true; // dynamic internal state
 		if (!variable.module && variable.writable && variable.export_name) return true; // writable props
+		if (is_reserved_keyword(variable.name)) return true;
 	}
 
 	return false;

test/runtime/samples/component-slot-fallback-6/Foo.svelte

@@ -0,0 +1 @@
+<slot />

test/runtime/samples/component-slot-fallback-6/Inner.svelte

@@ -0,0 +1,9 @@
+<script>
+	import Foo from './Foo.svelte';
+</script>
+
+<Foo>
+	<slot>
+		{JSON.stringify($$props)}
+	</slot>
+</Foo>

test/runtime/samples/component-slot-fallback-6/_config.js

@@ -0,0 +1,18 @@
+// $$props reactivity in slot fallback
+export default {
+	html: `
+		<input>
+		{"value":""}
+	`,
+
+	async test({ assert, target, window }) {
+		const input = target.querySelector("input");
+		input.value = "abc";
+		await input.dispatchEvent(new window.Event('input'));
+
+		assert.htmlEqual(target.innerHTML, `
+			<input>
+			{"value":"abc"}
+		`);
+	}
+};

test/runtime/samples/component-slot-fallback-6/main.svelte

@@ -0,0 +1,8 @@
+<script>
+	import Inner from "./Inner.svelte";
+	let value = '';
+</script>
+
+<input bind:value />
+
+<Inner {value} />