From 923d8f67dd9f8d3bdefacad25ed875e8bbe4c7c6 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 1 Jul 2025 13:17:15 -0400
Subject: [PATCH] fix

---
 .../client/visitors/AwaitExpression.js        | 18 +++++------
 .../client/visitors/CallExpression.js         |  7 ++--
 .../client/visitors/FunctionDeclaration.js    |  2 +-
 .../client/visitors/VariableDeclaration.js    | 32 ++++++++-----------
 .../client/visitors/shared/function.js        |  2 +-
 .../compiler/phases/3-transform/types.d.ts    |  3 ++
 6 files changed, 31 insertions(+), 33 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitExpression.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitExpression.js
index c0b3a5601c..c15709e48d 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitExpression.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitExpression.js
@@ -14,7 +14,7 @@ export function AwaitExpression(node, context) {
 		// preserve context if this is a top-level await in `<script>`
 		(context.state.is_instance && context.state.scope.function_depth === 1) ||
 		// or if this is a derived/template expression
-		(is_reactive_expression(context) && !is_last_evaluated_expression(context.path, node));
+		(is_reactive_expression(context) && !is_last_evaluated_expression(context, node));
 
 	if (dev || save) {
 		const expression = /** @type {Expression} */ (context.visit(node.argument));
@@ -28,6 +28,10 @@ export function AwaitExpression(node, context) {
  * @param {Context} context
  */
 function is_reactive_expression(context) {
+	if (context.state.in_derived) {
+		return true;
+	}
+
 	let i = context.path.length;
 
 	while (i--) {
@@ -41,10 +45,6 @@ function is_reactive_expression(context) {
 			return false;
 		}
 
-		if (parent.type === 'CallExpression' && get_rune(parent, context.state.scope) === '$derived') {
-			return true;
-		}
-
 		// @ts-expect-error we could probably use a neater/more robust mechanism
 		if (parent.metadata) {
 			return true;
@@ -55,14 +55,14 @@ function is_reactive_expression(context) {
 }
 
 /**
- * @param {AST.SvelteNode[]} path
+ * @param {Context} context
  * @param {Expression | SpreadElement | Property} node
  */
-function is_last_evaluated_expression(path, node) {
-	let i = path.length;
+function is_last_evaluated_expression(context, node) {
+	let i = context.path.length;
 
 	while (i--) {
-		const parent = /** @type {Expression | Property | SpreadElement} */ (path[i]);
+		const parent = /** @type {Expression | Property | SpreadElement} */ (context.path[i]);
 
 		// @ts-expect-error we could probably use a neater/more robust mechanism
 		if (parent.metadata) {
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js
index 7b0f4d4bc1..3e2f1414e6 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js
@@ -44,10 +44,11 @@ export function CallExpression(node, context) {
 
 		case '$derived':
 		case '$derived.by': {
-			let fn = /** @type {Expression} */ (context.visit(node.arguments[0]));
-			if (rune === '$derived') fn = b.thunk(fn);
+			let fn = /** @type {Expression} */ (
+				context.visit(node.arguments[0], { ...context.state, in_derived: rune === '$derived' })
+			);
 
-			return b.call('$.derived', fn);
+			return b.call('$.derived', rune === '$derived' ? b.thunk(fn) : fn);
 		}
 
 		case '$state.snapshot':
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/FunctionDeclaration.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/FunctionDeclaration.js
index 5dc8fa5cf9..cd299a710b 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/FunctionDeclaration.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/FunctionDeclaration.js
@@ -8,7 +8,7 @@ import * as b from '#compiler/builders';
  * @param {ComponentContext} context
  */
 export function FunctionDeclaration(node, context) {
-	const state = { ...context.state, in_constructor: false };
+	const state = { ...context.state, in_constructor: false, in_derived: false };
 
 	if (node.metadata?.hoisted === true) {
 		const params = build_hoisted_params(node, context);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
index 26362b8f44..d32f17b97a 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
@@ -199,29 +199,23 @@ export function VariableDeclaration(node, context) {
 				);
 
 				if (declarator.id.type === 'Identifier') {
+					let expression = /** @type {Expression} */ (
+						context.visit(value, {
+							...context.state,
+							in_derived: rune === '$derived'
+						})
+					);
+
 					if (is_async) {
 						const location = dev && is_ignored(init, 'await_waterfall') && locate_node(init);
-						const expression = /** @type {Expression} */ (context.visit(value));
-
-						declarations.push(
-							b.declarator(
-								declarator.id,
-								b.call(
-									b.await(
-										b.call(
-											'$.save',
-											b.call(
-												'$.async_derived',
-												b.thunk(expression, true),
-												location ? b.literal(location) : undefined
-											)
-										)
-									)
-								)
-							)
+						const call = b.call(
+							'$.async_derived',
+							b.thunk(expression, true),
+							location ? b.literal(location) : undefined
 						);
+
+						declarations.push(b.declarator(declarator.id, b.call(b.await(b.call('$.save', call)))));
 					} else {
-						let expression = /** @type {Expression} */ (context.visit(value));
 						if (rune === '$derived') expression = b.thunk(expression);
 
 						let call = b.call('$.derived', expression);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/function.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/function.js
index a0e9d0bf5e..691ac0b01e 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/function.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/function.js
@@ -9,7 +9,7 @@ import { build_hoisted_params } from '../../utils.js';
 export const visit_function = (node, context) => {
 	const metadata = node.metadata;
 
-	let state = { ...context.state, in_constructor: false };
+	let state = { ...context.state, in_constructor: false, in_derived: false };
 
 	if (node.type === 'FunctionExpression') {
 		const parent = /** @type {Node} */ (context.path.at(-1));
diff --git a/packages/svelte/src/compiler/phases/3-transform/types.d.ts b/packages/svelte/src/compiler/phases/3-transform/types.d.ts
index 887ad447b9..59c1bac268 100644
--- a/packages/svelte/src/compiler/phases/3-transform/types.d.ts
+++ b/packages/svelte/src/compiler/phases/3-transform/types.d.ts
@@ -8,5 +8,8 @@ export interface TransformState {
 	readonly scope: Scope;
 	readonly scopes: Map<AST.SvelteNode, Scope>;
 
+	/** True if we're directly inside a `$derived(...)` expression (but not `$derived.by(...)`) */
+	readonly in_derived: boolean;
+
 	readonly state_fields: Map<string, StateField>;
 }