From e541296da4a8eae0fea0578550e5fcef48ee05f5 Mon Sep 17 00:00:00 2001
From: 7nik <kifiranet@gmail.com>
Date: Sat, 13 Sep 2025 15:05:16 +0300
Subject: [PATCH] fix: ensure keys are validated

---
 .../3-transform/client/visitors/EachBlock.js  |  4 --
 .../src/internal/client/dom/blocks/each.js    |  6 +++
 .../svelte/src/internal/client/validate.js    | 38 ++++++++-----------
 3 files changed, 21 insertions(+), 27 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
index 225a4f617c..39f61272fc 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
@@ -337,10 +337,6 @@ export function EachBlock(node, context) {
 
 	const statements = [add_svelte_meta(b.call('$.each', ...args), node, 'each')];
 
-	if (dev && node.metadata.keyed) {
-		statements.unshift(b.stmt(b.call('$.validate_each_keys', thunk, key_function)));
-	}
-
 	if (has_await) {
 		context.state.init.push(
 			b.stmt(
diff --git a/packages/svelte/src/internal/client/dom/blocks/each.js b/packages/svelte/src/internal/client/dom/blocks/each.js
index 7b027ba502..3d8e7c8870 100644
--- a/packages/svelte/src/internal/client/dom/blocks/each.js
+++ b/packages/svelte/src/internal/client/dom/blocks/each.js
@@ -43,6 +43,7 @@ import { DEV } from 'esm-env';
 import { derived_safe_equal } from '../../reactivity/deriveds.js';
 import { current_batch } from '../../reactivity/batch.js';
 import { each_key_duplicate } from '../../errors.js';
+import { validate_each_keys } from '../../validate.js';
 
 /**
  * The row of a keyed each block that is currently updating. We track this
@@ -202,6 +203,11 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 		}
 		was_empty = length === 0;
 
+		// skip if #each block isn't keyed
+		if (DEV && get_key !== index) {
+			validate_each_keys(array, get_key);
+		}
+
 		/** `true` if there was a hydration mismatch. Needs to be a `let` or else it isn't treeshaken out */
 		let mismatch = false;
 
diff --git a/packages/svelte/src/internal/client/validate.js b/packages/svelte/src/internal/client/validate.js
index ec3d805447..7c8cf93fdc 100644
--- a/packages/svelte/src/internal/client/validate.js
+++ b/packages/svelte/src/internal/client/validate.js
@@ -7,35 +7,27 @@ import * as w from './warnings.js';
 import { capture_store_binding } from './reactivity/store.js';
 
 /**
- * @param {() => any} collection
+ * @param {Array<any>} array
  * @param {(item: any, index: number) => string} key_fn
  * @returns {void}
  */
-export function validate_each_keys(collection, key_fn) {
-	render_effect(() => {
-		const keys = new Map();
-		const maybe_array = collection();
-		const array = is_array(maybe_array)
-			? maybe_array
-			: maybe_array == null
-				? []
-				: Array.from(maybe_array);
-		const length = array.length;
-		for (let i = 0; i < length; i++) {
-			const key = key_fn(array[i], i);
-			if (keys.has(key)) {
-				const a = String(keys.get(key));
-				const b = String(i);
+export function validate_each_keys(array, key_fn) {
+	const keys = new Map();
+	const length = array.length;
+	for (let i = 0; i < length; i++) {
+		const key = key_fn(array[i], i);
+		if (keys.has(key)) {
+			const a = String(keys.get(key));
+			const b = String(i);
 
-				/** @type {string | null} */
-				let k = String(key);
-				if (k.startsWith('[object ')) k = null;
+			/** @type {string | null} */
+			let k = String(key);
+			if (k.startsWith('[object ')) k = null;
 
-				e.each_key_duplicate(a, b, k);
-			}
-			keys.set(key, i);
+			e.each_key_duplicate(a, b, k);
 		}
-	});
+		keys.set(key, i);
+	}
 }
 
 /**