fix: ignore declaration tags for animation directive (#18366)

Fixes #18365

.changeset/tangy-keys-drop.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ignore declaration tags for animation directive

packages/svelte/src/compiler/phases/2-analyze/visitors/shared/element.js

@@ -100,6 +100,7 @@ export function validate_element(node, context) {
 					(n) =>
 						n.type !== 'Comment' &&
 						n.type !== 'ConstTag' &&
+						n.type !== 'DeclarationTag' &&
 						(n.type !== 'Text' || n.data.trim() !== '')
 				).length > 1
 			) {

packages/svelte/tests/validator/samples/animation-each-with-declaration-tag/errors.json

@@ -0,0 +1 @@
+[]

packages/svelte/tests/validator/samples/animation-each-with-declaration-tag/input.svelte

@@ -0,0 +1,10 @@
+<script>
+  function flip(){}
+</script>
+
+<div>
+  {#each [] as n (n)}
+    {const a = n}
+    <div animate:flip={a}></div>
+  {/each}
+</div>