fix: migrate derivations without semicolons (#11704)

Closes #11689

Author: paoloricciuti

.changeset/kind-snakes-drive.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: migrate derivations without semicolons

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

@@ -369,11 +369,15 @@ const instance_script = {
 					/** @type {number} */ (node.body.expression.right.start),
 					'$derived('
 				);
-				state.str.update(
-					/** @type {number} */ (node.body.expression.right.end),
-					/** @type {number} */ (node.end),
-					');'
-				);
+				if (node.body.expression.right.end !== node.end) {
+					state.str.update(
+						/** @type {number} */ (node.body.expression.right.end),
+						/** @type {number} */ (node.end),
+						');'
+					);
+				} else {
+					state.str.appendRight(/** @type {number} */ (node.end), ');');
+				}
 				return;
 			} else {
 				for (const binding of reassigned_bindings) {

packages/svelte/tests/migrate/samples/derivations-no-colon/input.svelte

@@ -0,0 +1,7 @@
+<script>
+	let count = 0;
+	$: doubled = count * 2
+	$: ({ quadrupled } = { quadrupled: count * 4 })
+</script>
+
+{count} / {doubled} / {quadrupled}

packages/svelte/tests/migrate/samples/derivations-no-colon/output.svelte

@@ -0,0 +1,7 @@
+<script>
+	let count = 0;
+	let doubled = $derived(count * 2);
+	let { quadrupled } = $derived({ quadrupled: count * 4 });
+</script>
+
+{count} / {doubled} / {quadrupled}