From f398929fdd99f1d500fd994c9b2f80820a88d048 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Fri, 18 Oct 2024 18:04:53 +0100
Subject: [PATCH] fix: correct migration of uninitialised state (#13673)

* fix: correct migration of uninitialised state

* better fix
---
 .changeset/neat-rabbits-divide.md                   |  5 +++++
 packages/svelte/src/compiler/migrate/index.js       |  7 ++++++-
 .../migrate/samples/state-no-initial/input.svelte   | 13 +++++++++++++
 .../migrate/samples/state-no-initial/output.svelte  | 13 +++++++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/neat-rabbits-divide.md
 create mode 100644 packages/svelte/tests/migrate/samples/state-no-initial/input.svelte
 create mode 100644 packages/svelte/tests/migrate/samples/state-no-initial/output.svelte

diff --git a/.changeset/neat-rabbits-divide.md b/.changeset/neat-rabbits-divide.md
new file mode 100644
index 0000000000..ffe57a6f18
--- /dev/null
+++ b/.changeset/neat-rabbits-divide.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: correct migration of uninitialised state
diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index 69c840aedb..3d70d54d9f 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/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))
+						);
 					})
 				);
 
diff --git a/packages/svelte/tests/migrate/samples/state-no-initial/input.svelte b/packages/svelte/tests/migrate/samples/state-no-initial/input.svelte
new file mode 100644
index 0000000000..c2c4183465
--- /dev/null
+++ b/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>
diff --git a/packages/svelte/tests/migrate/samples/state-no-initial/output.svelte b/packages/svelte/tests/migrate/samples/state-no-initial/output.svelte
new file mode 100644
index 0000000000..2f6a9933ee
--- /dev/null
+++ b/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>
\ No newline at end of file