From c7851789d71cc3d0b5d89ce9c759a39be6caa51a Mon Sep 17 00:00:00 2001
From: 7nik <kifiranet@gmail.com>
Date: Sat, 26 Jul 2025 21:27:22 +0300
Subject: [PATCH] fix: always mark props as stateful (#16504)

---
 .changeset/gorgeous-jeans-begin.md                |  5 +++++
 .../phases/2-analyze/visitors/Identifier.js       |  5 ++++-
 .../props-default-value-function/_config.js       | 15 +++++++++++++++
 .../props-default-value-function/inner.svelte     |  4 ++++
 .../props-default-value-function/main.svelte      | 14 ++++++++++++++
 .../props-default-value-function/wrapper.svelte   |  7 +++++++
 .../props-default-value-function/wrapper2.svelte  |  7 +++++++
 7 files changed, 56 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/gorgeous-jeans-begin.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/inner.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper2.svelte

diff --git a/.changeset/gorgeous-jeans-begin.md b/.changeset/gorgeous-jeans-begin.md
new file mode 100644
index 0000000000..586c4d8a57
--- /dev/null
+++ b/.changeset/gorgeous-jeans-begin.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: always mark props as stateful
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/Identifier.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/Identifier.js
index cced326f9b..4dfdfe5af1 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/Identifier.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/Identifier.js
@@ -93,7 +93,10 @@ export function Identifier(node, context) {
 			context.state.expression.references.add(binding);
 			context.state.expression.has_state ||=
 				binding.kind !== 'static' &&
-				!binding.is_function() &&
+				(binding.kind === 'prop' ||
+					binding.kind === 'bindable_prop' ||
+					binding.kind === 'rest_prop' ||
+					!binding.is_function()) &&
 				!context.state.scope.evaluate(node).is_known;
 		}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/_config.js b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/_config.js
new file mode 100644
index 0000000000..6b281f04f0
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/_config.js
@@ -0,0 +1,15 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+
+	test({ assert, target }) {
+		const btn = target.querySelector('button');
+
+		assert.htmlEqual(target.innerHTML, `<button>inc</button> Inner: 0 Inner: 0`);
+		btn?.click();
+		flushSync();
+		assert.htmlEqual(target.innerHTML, `<button>inc</button> Inner: 1 Inner: 1`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/inner.svelte b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/inner.svelte
new file mode 100644
index 0000000000..6bde0a15a8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/inner.svelte
@@ -0,0 +1,4 @@
+<script>
+	let { getter } = $props()
+</script>
+Inner: {getter()}
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/main.svelte b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/main.svelte
new file mode 100644
index 0000000000..2cb2f67b82
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/main.svelte
@@ -0,0 +1,14 @@
+<script>
+	import Wrapper1 from "./wrapper.svelte"
+	import Wrapper2 from "./wrapper2.svelte"
+	let count = $state(0);
+
+	let getter = $derived.by(() => {
+		const copy = count;
+		return () => copy;
+	});
+</script>
+
+<button onclick={() => count++}>inc</button>
+<Wrapper1 {getter}/>
+<Wrapper2 {getter}/>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper.svelte b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper.svelte
new file mode 100644
index 0000000000..525494ddfb
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper.svelte
@@ -0,0 +1,7 @@
+<script >
+  import Inner from "./inner.svelte";
+
+  const { getter = () => -1} = $props();
+</script>
+
+<Inner {getter} />
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper2.svelte b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper2.svelte
new file mode 100644
index 0000000000..9498f432d8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper2.svelte
@@ -0,0 +1,7 @@
+<script >
+  import Inner from "./inner.svelte";
+
+  const { getter = $bindable(() => -1)} = $props();
+</script>
+
+<Inner {getter} />