fix: correct migration of uninitialised state (#13673)

* fix: correct migration of uninitialised state

* better fix

Author: trueadm

.changeset/neat-rabbits-divide.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: correct migration of uninitialised state

packages/svelte/src/compiler/migrate/index.js

@@ -564,7 +564,12 @@ const instance_script = {
 							labeled_statement = /** @type {LabeledStatement} */ (labeled);
 						}
 
-						return !update && (declaration || (labeled && assignment) || (!labeled && !assignment));
+						return (
+							!update &&
+							((declaration && binding.initial) ||
+								(labeled && assignment) ||
+								(!labeled && !assignment))
+						);
 					})
 				);
 

packages/svelte/tests/migrate/samples/state-no-initial/input.svelte

@@ -0,0 +1,13 @@
+<script lang="ts">
+	let bounds: DOMRect | undefined;
+	$: position = calculatePosition(bounds);
+
+	const openDropdown = () => {
+    bounds = getInputPosition();
+  };
+
+	const getInputPosition = () => {};
+  const calculatePosition = (boundary?: DOMRect) => ({});
+</script>
+
+<div style:top={position.top}></div>

packages/svelte/tests/migrate/samples/state-no-initial/output.svelte

@@ -0,0 +1,13 @@
+<script lang="ts">
+	let bounds: DOMRect | undefined = $state();
+
+	const openDropdown = () => {
+    bounds = getInputPosition();
+  };
+
+	const getInputPosition = () => {};
+  const calculatePosition = (boundary?: DOMRect) => ({});
+	let position = $derived(calculatePosition(bounds));
+</script>
+
+<div style:top={position.top}></div>