fix: more robust moving of each item nodes (#11254)

* move then link

* fix: more robust moving of each item nodes

* test

Author: Rich-Harris

.changeset/brave-carrots-draw.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: more robust moving of each item nodes

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

@@ -323,26 +323,25 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 				if (matched.length < stashed.length) {
 					// more efficient to move later items to the front
 					var start = stashed[0];
-					var local_anchor = start.o;
 					var j;
 
 					prev = start.prev;
 
 					var a = matched[0];
 					var b = matched[matched.length - 1];
 
-					link(a.prev, b.next);
-					link(prev, a);
-					link(b, start);
-
 					for (j = 0; j < matched.length; j += 1) {
-						move(matched[j], local_anchor);
+						move(matched[j], start, anchor);
 					}
 
 					for (j = 0; j < stashed.length; j += 1) {
 						seen.delete(stashed[j]);
 					}
 
+					link(a.prev, b.next);
+					link(prev, a);
+					link(b, start);
+
 					current = start;
 					prev = b;
 					i -= 1;
@@ -352,7 +351,7 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 				} else {
 					// more efficient to move earlier items to the back
 					seen.delete(item);
-					move(item, current ? current.o : anchor);
+					move(item, current, anchor);
 
 					link(item.prev, item.next);
 					link(item, prev.next);
@@ -492,21 +491,19 @@ function create_item(open, anchor, prev, next, value, key, index, render_fn, fla
 
 /**
  * @param {import('#client').EachItem} item
+ * @param {import('#client').EachItem | null} next
  * @param {Text | Element | Comment} anchor
  */
-function move(item, anchor) {
-	anchor.before(item.o);
+function move(item, next, anchor) {
+	var end = item.next ? item.next.o : anchor;
+	var dest = next ? next.o : anchor;
 
-	var dom = item.e.dom;
+	var node = /** @type {import('#client').TemplateNode} */ (item.o);
 
-	if (dom !== null) {
-		if (is_array(dom)) {
-			for (var i = 0; i < dom.length; i++) {
-				anchor.before(dom[i]);
-			}
-		} else {
-			anchor.before(dom);
-		}
+	while (node !== end) {
+		var next_node = /** @type {import('#client').TemplateNode} */ (node.nextSibling);
+		dest.before(node);
+		node = next_node;
 	}
 }
 

packages/svelte/tests/runtime-runes/samples/each-keyed-child-effect/_config.js

@@ -0,0 +1,43 @@
+import { flushSync } from 'svelte';
+import { ok, test } from '../../test';
+
+let ascending = `
+<button>reverse</button>
+<p>1</p>
+<p>(1)</p>
+<p>2</p>
+<p>(2)</p>
+<p>3</p>
+<p>(3)</p>
+`;
+
+let descending = `
+<button>reverse</button>
+<p>3</p>
+<p>(3)</p>
+<p>2</p>
+<p>(2)</p>
+<p>1</p>
+<p>(1)</p>
+`;
+
+export default test({
+	html: ascending,
+
+	async test({ assert, target }) {
+		const btn = target.querySelector('button');
+		ok(btn);
+
+		flushSync(() => btn.click());
+		assert.htmlEqual(target.innerHTML, descending);
+
+		flushSync(() => btn.click());
+		assert.htmlEqual(target.innerHTML, ascending);
+
+		flushSync(() => btn.click());
+		assert.htmlEqual(target.innerHTML, descending);
+
+		flushSync(() => btn.click());
+		assert.htmlEqual(target.innerHTML, ascending);
+	}
+});

packages/svelte/tests/runtime-runes/samples/each-keyed-child-effect/main.svelte

@@ -0,0 +1,12 @@
+<script>
+	let array = $state([1, 2, 3]);
+</script>
+
+<button onclick={() => array.reverse()}>reverse</button>
+
+{#each array as item (item)}
+	<p>{item}</p>
+	{#if true}
+		<p>({item})</p>
+	{/if}
+{/each}