From 1dd383ea5416551ac0314d35ef58254f28232bb0 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sat, 3 May 2025 18:48:46 +0200
Subject: [PATCH] enforce linear order

---
 .../internal/client/reactivity/deriveds.js    | 19 ++++++++++++++++++-
 .../_config.js                                |  1 +
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index 5c33a827dd..c508e515c0 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -106,14 +106,27 @@ export function async_derived(fn, location) {
 	var promise = /** @type {Promise<V>} */ (/** @type {unknown} */ (undefined));
 	var signal = source(/** @type {V} */ (UNINITIALIZED));
 
+	/** @type {Promise<V> | null} */
+	var prev = null;
+
 	// only suspend in async deriveds created on initialisation
 	var should_suspend = !active_reaction;
 
 	render_effect(() => {
 		if (DEV) from_async_derived = active_effect;
-		promise = Promise.resolve(fn());
+		var p = fn();
 		if (DEV) from_async_derived = null;
 
+		promise =
+			prev === null
+				? Promise.resolve(p)
+				: prev.then(
+						() => p,
+						() => p
+					);
+
+		prev = promise;
+
 		var restore = capture();
 
 		var batch = /** @type {Batch} */ (current_batch);
@@ -129,6 +142,8 @@ export function async_derived(fn, location) {
 
 		promise.then(
 			(v) => {
+				prev = null;
+
 				if ((parent.f & DESTROYED) !== 0) {
 					return;
 				}
@@ -160,6 +175,8 @@ export function async_derived(fn, location) {
 				}
 			},
 			(e) => {
+				prev = null;
+
 				handle_error(e, parent, null, parent.ctx);
 			}
 		);
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/_config.js b/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/_config.js
index c8f20d9597..99f91503e1 100644
--- a/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/_config.js
@@ -34,6 +34,7 @@ export default test({
 		await Promise.resolve();
 		await Promise.resolve();
 		await Promise.resolve();
+		await Promise.resolve();
 		await tick();
 
 		assert.htmlEqual(target.innerHTML, '<p>hello</p>');