fix: improve each block item equality for immutable mode

.changeset/forty-dogs-divide.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: improve each block item equality for immutable mode

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

@@ -28,7 +28,7 @@ import {
 	DOMBooleanAttributes,
 	EACH_INDEX_REACTIVE,
 	EACH_IS_CONTROLLED,
-	EACH_IS_IMMUTABLE,
+	EACH_IS_STRICT_EQUALS,
 	EACH_ITEM_REACTIVE,
 	EACH_KEYED
 } from '../../../../../constants.js';
@@ -2259,8 +2259,8 @@ export const template_visitors = {
 			each_type |= EACH_IS_CONTROLLED;
 		}
 
-		if (context.state.analysis.immutable) {
-			each_type |= EACH_IS_IMMUTABLE;
+		if (context.state.analysis.runes) {
+			each_type |= EACH_IS_STRICT_EQUALS;
 		}
 
 		// Find the parent each blocks which contain the arrays to invalidate

packages/svelte/src/constants.js

@@ -5,7 +5,7 @@ export const EACH_KEYED = 1 << 2;
 /** See EachBlock interface metadata.is_controlled for an explanation what this is */
 export const EACH_IS_CONTROLLED = 1 << 3;
 export const EACH_IS_ANIMATED = 1 << 4;
-export const EACH_IS_IMMUTABLE = 1 << 6;
+export const EACH_IS_STRICT_EQUALS = 1 << 6;
 
 export const PROPS_IS_IMMUTABLE = 1;
 export const PROPS_IS_RUNES = 1 << 1;

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

@@ -2,7 +2,7 @@ import {
 	EACH_INDEX_REACTIVE,
 	EACH_IS_ANIMATED,
 	EACH_IS_CONTROLLED,
-	EACH_IS_IMMUTABLE,
+	EACH_IS_STRICT_EQUALS,
 	EACH_ITEM_REACTIVE,
 	EACH_KEYED
 } from '../../constants.js';
@@ -852,9 +852,9 @@ function each_item_block(item, key, index, render_fn, flags) {
 
 	const item_value = each_item_not_reactive
 		? item
-		: (flags & EACH_IS_IMMUTABLE) === 0
-			? mutable_source(item)
-			: source(item);
+		: (flags & EACH_IS_STRICT_EQUALS) !== 0
+			? source(item)
+			: mutable_source(item);
 
 	const index_value = (flags & EACH_INDEX_REACTIVE) === 0 ? index : source(index);
 	const block = create_each_item_block(item_value, index_value, key);

packages/svelte/tests/runtime-legacy/samples/immutable-each-equals/_config.js

@@ -0,0 +1,16 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	immutable: true,
+
+	test({ assert, target }) {
+		const btn = target.querySelector('button');
+
+		flushSync(() => {
+			btn?.click();
+		});
+
+		assert.htmlEqual(target.innerHTML, `<button>Update</button><ul><li>test !!!</li></ul>`);
+	}
+});

packages/svelte/tests/runtime-legacy/samples/immutable-each-equals/main.svelte

@@ -0,0 +1,17 @@
+<script>
+	let items = [{id:1,value: "test"}]
+	const update = () => {
+		const clone = items.slice();
+		clone[0].value += " !!!";
+		items = clone;
+	}
+</script>
+
+<button on:click={update} >Update</button>
+
+<ul>
+	{#each items as item (item.id)}
+		<li>{item.value}</li>
+	{/each}
+</ul>
+