determine needsAnchor lazily

src/generators/dom/preprocess.ts

@@ -421,10 +421,8 @@ function preprocessChildren(
 		const preprocessor = preprocessors[child.type];
 		if (preprocessor) preprocessor(generator, block, state, child, inEachBlock, elementStack, componentStack, stripWhitespace, cleaned[i + 1] || nextSibling);
 
-		if (lastChild) {
-			lastChild.next = child;
-			lastChild.needsAnchor = !child._state || !child._state.name;
-		}
+		if (lastChild) lastChild.next = child;
+		child.prev = lastChild;
 
 		lastChild = child;
 	});
@@ -446,10 +444,6 @@ function preprocessChildren(
 		}
 	}
 
-	if (lastChild) {
-		lastChild.needsAnchor = !state.parentNode;
-	}
-
 	node.children = cleaned;
 }
 

src/generators/dom/visitors/EachBlock.ts

@@ -18,7 +18,9 @@ export default function visitEachBlock(
 	const each_block_value = node._block.listName;
 	const iterations = block.getUniqueName(`${each_block}_iterations`);
 	const params = block.params.join(', ');
-	const anchor = node.needsAnchor
+
+	const needsAnchor = node.next ? (!node.next._state || !node.next._state.name) : !state.parentNode;
+	const anchor = needsAnchor
 		? block.getUniqueName(`${each_block}_anchor`)
 		: (node.next && node.next._state.name) || 'null';
 
@@ -53,7 +55,7 @@ export default function visitEachBlock(
 
 	const isToplevel = !state.parentNode;
 
-	if (node.needsAnchor) {
+	if (needsAnchor) {
 		block.addElement(
 			anchor,
 			`@createComment()`,

src/generators/dom/visitors/IfBlock.ts

@@ -78,7 +78,9 @@ export default function visitIfBlock(
 	componentStack: Node[]
 ) {
 	const name = generator.getUniqueName(`if_block`);
-	const anchor = node.needsAnchor
+
+	const needsAnchor = node.next ? (!node.next._state || !node.next._state.name) : !state.parentNode;
+	const anchor = needsAnchor
 		? block.getUniqueName(`${name}_anchor`)
 		: (node.next && node.next._state.name) || 'null';
 	const params = block.params.join(', ');
@@ -117,7 +119,7 @@ export default function visitIfBlock(
 		`${if_name}${name}.claim( ${state.parentNodes} );`
 	);
 
-	if (node.needsAnchor) {
+	if (needsAnchor) {
 		block.addElement(
 			anchor,
 			`@createComment()`,