fix: read index as a source in legacy keyed each block (#14208)

Fixes #14203

Author: paoloricciuti

.changeset/late-dodos-film.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: read index as a source in legacy keyed each block

packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js

@@ -196,7 +196,7 @@ export function EachBlock(node, context) {
 					// forbidden in runes mode
 					return b.member(
 						each_node_meta.array_name ? b.call(each_node_meta.array_name) : collection,
-						index,
+						(flags & EACH_INDEX_REACTIVE) !== 0 ? get_value(index) : index,
 						true
 					);
 				}
@@ -208,7 +208,7 @@ export function EachBlock(node, context) {
 
 				const left = b.member(
 					each_node_meta.array_name ? b.call(each_node_meta.array_name) : collection,
-					index,
+					(flags & EACH_INDEX_REACTIVE) !== 0 ? get_value(index) : index,
 					true
 				);
 

packages/svelte/tests/runtime-legacy/samples/keyed-each-bind-read-index/Component.svelte

@@ -0,0 +1,5 @@
+<script>
+	export let item;
+	console.log(item);
+	item = 1;
+</script>

packages/svelte/tests/runtime-legacy/samples/keyed-each-bind-read-index/_config.js

@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		const p = target.querySelector('p');
+		assert.equal(p?.innerHTML, '1');
+		assert.deepEqual(logs, [0]);
+	}
+});

packages/svelte/tests/runtime-legacy/samples/keyed-each-bind-read-index/main.svelte

@@ -0,0 +1,10 @@
+<script>
+	import Component from './Component.svelte';
+	const items = [0];
+</script>
+
+{#each items as item, idx(item)}
+	<Component bind:item />
+{/each}
+
+<p>{items}</p>