fix: use `get` in constructor for deriveds (#15300)

Co-authored-by: Rich Harris <rich.harris@vercel.com>

.changeset/new-cherries-leave.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: use `get` in constructor for deriveds

packages/svelte/src/compiler/phases/3-transform/client/visitors/MemberExpression.js

@@ -11,7 +11,9 @@ export function MemberExpression(node, context) {
 	if (node.property.type === 'PrivateIdentifier') {
 		const field = context.state.private_state.get(node.property.name);
 		if (field) {
-			return context.state.in_constructor ? b.member(node, 'v') : b.call('$.get', node);
+			return context.state.in_constructor && (field.kind === 'raw_state' || field.kind === 'state')
+				? b.member(node, 'v')
+				: b.call('$.get', node);
 		}
 	}
 

packages/svelte/tests/runtime-runes/samples/deriveds-in-constructor/_config.js

@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	html: `<p>state,derived state,derived.by derived state</p>`
+});

packages/svelte/tests/runtime-runes/samples/deriveds-in-constructor/main.svelte

@@ -0,0 +1,18 @@
+<script>
+	class Foo {
+		#state = $state('state')
+		#derived = $derived('derived ' + this.#state);
+		#derivedBy = $derived.by(() => {
+			return 'derived.by ' + this.#derived 
+		});
+		
+		initial
+		
+		constructor() {
+			this.initial = [this.#state, this.#derived, this.#derivedBy]
+		}
+	}
+	const foo = new Foo()
+</script>
+
+<p>{foo.initial}</p>