use EACH_IS_ANIMATED flag

Author: Refzlund

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

@@ -80,16 +80,7 @@ export function EachBlock(node, context) {
 		flags |= EACH_ITEM_IMMUTABLE;
 	}
 
-	// Since `animate:` can only appear on elements that are the sole child of a keyed each block,
-	// we can determine at compile time whether the each block is animated or not (in which
-	// case it should measure animated elements before and after reconciliation).
-	if (
-		node.key &&
-		node.body.nodes.some((child) => {
-			if (child.type !== 'RegularElement' && child.type !== 'SvelteElement') return false;
-			return child.attributes.some((attr) => attr.type === 'AnimateDirective');
-		})
-	) {
+	if (node.key && node.body.nodes.some(is_animate_directive)) {
 		flags |= EACH_IS_ANIMATED;
 	}
 
@@ -348,3 +339,14 @@ function collect_transitive_dependencies(binding, seen = new Set()) {
 
 	return [...seen];
 }
+
+/** @param {AST.Text | AST.Tag | AST.ElementLike | AST.Comment | AST.Block} child */
+function is_animate_directive(child) {
+	if (child.type === 'RenderTag') {
+		for (const snippetBlock of child.metadata.snippets) {
+			return snippetBlock.body.nodes.some(is_animate_directive);
+		}
+	}
+	if (child.type !== 'RegularElement' && child.type !== 'SvelteElement') return false;
+	return child.attributes.some((attr) => attr.type === 'AnimateDirective');
+}

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

@@ -276,15 +276,14 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
  * @returns {void}
  */
 function reconcile(array, state, anchor, render_fn, flags, is_inert, get_key, get_collection) {
+	var is_animated = (flags & EACH_IS_ANIMATED) !== 0;
 	var should_update = (flags & (EACH_ITEM_REACTIVE | EACH_INDEX_REACTIVE)) !== 0;
 
 	var length = array.length;
 	var items = state.items;
 	var first = state.first;
 	var current = first;
-
-	var is_animated = items.get(get_key(array[0], 0))?.a !== null;
-
+	
 	/** @type {undefined | Set<EachItem>} */
 	var seen;