failing test (that uncovered other unrelated bug) + fix

Author: dummdidumm

packages/svelte/src/internal/client/runtime.js

@@ -664,15 +664,18 @@ function reconnect(derived) {
 
 /**
  * Removes the WAS_MARKED flag from the derived and its dependencies
- * @param {Derived} derived
+ * @param {Value} derived
  */
 function remove_marked_flag(derived) {
-	if ((derived.f & WAS_MARKED) === 0) return;
-	derived.f ^= WAS_MARKED;
+	// We cannot stop at the first non-marked derived because batch_values can
+	// cause "holes" of unmarked deriveds in an otherwise marked graph
+	if ((derived.f & DERIVED) === 0) return;
+
+	derived.f &= ~WAS_MARKED;
 
 	// Only deriveds with dependencies can be marked
-	for (const dep of /** @type {Value[]} */ (derived.deps)) {
-		remove_marked_flag(/** @type {Derived} */ (dep));
+	for (const dep of /** @type {Value[]} */ (/** @type {Derived} */ (derived).deps)) {
+		remove_marked_flag(dep);
 	}
 }
 

packages/svelte/tests/runtime-runes/samples/async-derived-in-multiple-effects/Component.svelte

@@ -0,0 +1,27 @@
+<script>
+	import { untrack } from "svelte";
+
+	let { double } = $props();
+
+	// Test setup:
+	// - component initialized while pending work
+	// - derived that depends on mulitple sources
+	// - indirect updates to subsequent deriveds
+	// - two sibling effects where the former influences the latter
+	// - first effect reads derived of second inside untrack
+	let x = $state(0);
+	const other = $derived(double + x);
+	const another = $derived(other + 1);
+	const another2 = $derived(another + 1);
+
+	$effect(() => {
+		untrack(() => {
+			another2;
+			x++
+		});
+	});
+
+	$effect(() => {
+		console.log(another2);
+	})
+</script>

packages/svelte/tests/runtime-runes/samples/async-derived-in-multiple-effects/_config.js

@@ -0,0 +1,18 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		const button = target.querySelector('button');
+
+		button?.click();
+		await tick();
+		// TODO this is wrong: it should be [5]
+		assert.deepEqual(logs, [4]);
+
+		button?.click();
+		await tick();
+		// TODO this is wrong: it should be [5, 7]
+		assert.deepEqual(logs, [4, 7]);
+	}
+});

packages/svelte/tests/runtime-runes/samples/async-derived-in-multiple-effects/main.svelte

@@ -0,0 +1,19 @@
+<script>
+	import Component from './Component.svelte';
+	let count = $state(0);
+	const double = $derived(count * 2);
+</script>
+
+<svelte:boundary>
+	{await new Promise((r) => {
+		// long enough for the test to do all its other stuff while this is pending
+		setTimeout(r, 10);
+	})}
+	{#snippet pending()}{/snippet}
+</svelte:boundary>
+
+<button onclick={() => count += 1}>{count}</button>
+
+{#if count > 0}
+	<Component {double} />
+{/if}