From 8a7e54065cd343a72c9b5c8a7b7ed9ac6a865266 Mon Sep 17 00:00:00 2001
From: Simon Holthausen <simon.holthausen@vercel.com>
Date: Wed, 13 Mar 2024 12:41:29 +0100
Subject: [PATCH] fix: handle component binding mutation

https://github.com/sveltejs/svelte/issues/10359#issuecomment-1991885046
---
 .changeset/witty-readers-provide.md           |  5 +++
 .../src/internal/client/reactivity/props.js   |  5 ++-
 .../component-binding-deep2/Widget.svelte     |  5 +++
 .../component-binding-deep2/_config.js        | 32 +++++++++++++++++++
 .../component-binding-deep2/main.svelte       | 11 +++++++
 5 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/witty-readers-provide.md
 create mode 100644 packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/Widget.svelte
 create mode 100644 packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/_config.js
 create mode 100644 packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/main.svelte

diff --git a/.changeset/witty-readers-provide.md b/.changeset/witty-readers-provide.md
new file mode 100644
index 0000000000..60a6bdf009
--- /dev/null
+++ b/.changeset/witty-readers-provide.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: handle component binding mutation
diff --git a/packages/svelte/src/internal/client/reactivity/props.js b/packages/svelte/src/internal/client/reactivity/props.js
index b3559ae99f..72123fb521 100644
--- a/packages/svelte/src/internal/client/reactivity/props.js
+++ b/packages/svelte/src/internal/client/reactivity/props.js
@@ -175,10 +175,13 @@ export function prop(props, key, flags, initial) {
 	// intermediate mode — prop is written to, but the parent component had
 	// `bind:foo` which means we can just call `$$props.foo = value` directly
 	if (setter) {
-		return function (/** @type {V} */ value) {
+		return function (/** @type {V} */ value, mutation = false) {
 			if (arguments.length === 1) {
 				/** @type {Function} */ (setter)(value);
 				return value;
+			} else if (mutation) {
+				/** @type {Function} */ (setter)(getter());
+				return value;
 			} else {
 				return getter();
 			}
diff --git a/packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/Widget.svelte b/packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/Widget.svelte
new file mode 100644
index 0000000000..c28dfbda90
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/Widget.svelte
@@ -0,0 +1,5 @@
+<script>
+	export let value;
+</script>
+
+<input bind:value={value.name}>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/_config.js b/packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/_config.js
new file mode 100644
index 0000000000..0479b7c529
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/_config.js
@@ -0,0 +1,32 @@
+import { ok, test } from '../../test';
+
+export default test({
+	html: `
+		<input>
+		<p>foo</p>
+	`,
+
+	ssrHtml: `
+		<input value=foo>
+		<p>foo</p>
+	`,
+
+	async test({ assert, component, target, window }) {
+		const event = new window.MouseEvent('input');
+		const input = target.querySelector('input');
+		ok(input);
+
+		input.value = 'blah';
+		await input.dispatchEvent(event);
+		await Promise.resolve();
+
+		assert.deepEqual(component.deep, { name: 'blah' });
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+			<input>
+			<p>blah</p>
+		`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/main.svelte b/packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/main.svelte
new file mode 100644
index 0000000000..db8cd83b91
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/component-binding-deep2/main.svelte
@@ -0,0 +1,11 @@
+<script>
+	import Widget from './Widget.svelte';
+
+	export let deep = {
+		name: 'foo'
+	};
+</script>
+
+<Widget bind:value={deep}/>
+
+<p>{deep.name}</p>
\ No newline at end of file