fix: improve ssr code generation for class property $derived

Author: trueadm

.changeset/rotten-poems-applaud.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: improve ssr code generation for class property $derived

packages/svelte/src/compiler/phases/3-transform/server/transform-server.js

@@ -545,7 +545,7 @@ const javascript_visitors_runes = {
 		if (node.value != null && node.value.type === 'CallExpression') {
 			const rune = get_rune(node.value, state.scope);
 
-			if (rune === '$state' || rune === '$state.frozen' || rune === '$derived') {
+			if (rune === '$state' || rune === '$state.frozen') {
 				return {
 					...node,
 					value:
@@ -554,6 +554,24 @@ const javascript_visitors_runes = {
 							: /** @type {import('estree').Expression} */ (visit(node.value.arguments[0]))
 				};
 			}
+			if (rune === '$derived') {
+				return {
+					type: 'MethodDefinition',
+					kind: 'get',
+					key: node.key,
+					value: b.function(
+						null,
+						[],
+						b.block([
+							b.return(
+								node.value.arguments.length === 0
+									? null
+									: /** @type {import('estree').Expression} */ (visit(node.value.arguments[0]))
+							)
+						])
+					)
+				};
+			}
 			if (rune === '$derived.by') {
 				return {
 					...node,

packages/svelte/tests/runtime-runes/samples/class-state-derived-2/_config.js

@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	html: `2`
+});

packages/svelte/tests/runtime-runes/samples/class-state-derived-2/main.svelte

@@ -0,0 +1,15 @@
+<script>
+	export class Counter {
+		count = $state(0);
+		doubled = $derived(this.count * 2);
+
+		constructor(initialCount = 0) {
+			this.count = initialCount;
+		}
+	}
+
+	const counter = new Counter(1);
+</script>
+
+{counter.doubled}
+