fix: ensure each block inert items are disposed of if the each block is also inert

.changeset/curly-dogs-breathe.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure each block inert items are disposed of if the each block is also inert

packages/svelte/src/internal/client/dom/blocks/each.js

@@ -35,7 +35,7 @@ import { source, mutable_source, internal_set } from '../../reactivity/sources.j
 import { array_from, is_array } from '../../../shared/utils.js';
 import { INERT } from '../../constants.js';
 import { queue_micro_task } from '../task.js';
-import { active_effect } from '../../runtime.js';
+import { active_effect, active_reaction } from '../../runtime.js';
 
 /**
  * The row of a keyed each block that is currently updating. We track this
@@ -204,7 +204,8 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 		}
 
 		if (!hydrating) {
-			reconcile(array, state, anchor, render_fn, flags, get_key);
+			var effect = /** @type {Effect} */ (active_reaction);
+			reconcile(array, state, anchor, render_fn, flags, (effect.f & INERT) !== 0, get_key);
 		}
 
 		if (fallback_fn !== null) {
@@ -248,10 +249,11 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
  * @param {Element | Comment | Text} anchor
  * @param {(anchor: Node, item: MaybeSource<V>, index: number | Source<number>) => void} render_fn
  * @param {number} flags
+ * @param {boolean} is_inert
  * @param {(value: V, index: number) => any} get_key
  * @returns {void}
  */
-function reconcile(array, state, anchor, render_fn, flags, get_key) {
+function reconcile(array, state, anchor, render_fn, flags, is_inert, get_key) {
 	var is_animated = (flags & EACH_IS_ANIMATED) !== 0;
 	var should_update = (flags & (EACH_ITEM_REACTIVE | EACH_INDEX_REACTIVE)) !== 0;
 
@@ -390,9 +392,9 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 			stashed = [];
 
 			while (current !== null && current.k !== key) {
-				// If the item has an effect that is already inert, skip over adding it
-				// to our seen Set as the item is already being handled
-				if ((current.e.f & INERT) === 0) {
+				// If the each block isn't inert and an item has an effect that is already inert,
+				// skip over adding it to our seen Set as the item is already being handled
+				if (is_inert || (current.e.f & INERT) === 0) {
 					(seen ??= new Set()).add(current);
 				}
 				stashed.push(current);
@@ -415,8 +417,8 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 		var to_destroy = seen === undefined ? [] : array_from(seen);
 
 		while (current !== null) {
-			// Inert effects are currently outroing and will be removed once the transition is finished
-			if ((current.e.f & INERT) === 0) {
+			// If the each block isn't inert, then inert effects are currently outroing and will be removed once the transition is finished
+			if (is_inert || (current.e.f & INERT) === 0) {
 				to_destroy.push(current);
 			}
 			current = current.next;

packages/svelte/src/internal/client/reactivity/effects.js

@@ -577,14 +577,17 @@ export function resume_effect(effect) {
  */
 function resume_children(effect, local) {
 	if ((effect.f & INERT) === 0) return;
-	effect.f ^= INERT;
 
 	// If a dependency of this effect changed while it was paused,
 	// apply the change now
 	if (check_dirtiness(effect)) {
 		update_effect(effect);
 	}
 
+	// Ensure we toggle the flag after possibly updating the effect so that
+	// each block logic can correctly operate on inert items
+	effect.f ^= INERT;
+
 	var child = effect.first;
 
 	while (child !== null) {

packages/svelte/tests/runtime-runes/samples/transition-each-3/_config.js

@@ -0,0 +1,31 @@
+import { flushSync } from '../../../../src/index-client.js';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, raf, target }) {
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>Toggle</button><div><div>1</div><div>2</div><div>3</div></div>'
+		);
+
+		const btn1 = target.querySelector('button');
+		btn1?.click();
+		flushSync();
+		raf.tick(250);
+
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>Toggle</button><div style="opacity: 0.5;"><div>1</div><div>2</div><div>3</div></div>'
+		);
+
+		await Promise.resolve();
+
+		flushSync();
+		raf.tick(500);
+
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>Toggle</button><div style=""><div>3</div><div>4</div></div>'
+		);
+	}
+});

packages/svelte/tests/runtime-runes/samples/transition-each-3/main.svelte

@@ -0,0 +1,28 @@
+<script>
+	function fade(_) {
+		return {
+			duration: 500,
+			css: t => `opacity: ${t}`,
+		}
+	}
+
+	let toggle = $state(true);
+	let items = $state([ 1, 2, 3 ]);
+
+	const handle_toggle = async () => {
+		toggle = false;
+		await Promise.resolve();
+		items = [3, 4];
+		toggle = true;
+	};
+</script>
+
+<button onclick={handle_toggle}>Toggle</button>
+
+{#if toggle}
+	<div transition:fade>
+		{#each items as item (item)}
+			<div>{item}</div>
+		{/each}
+	</div>
+{/if}