fix: correctly validate nested if block tags

Fixes #13210

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

@@ -12,15 +12,7 @@ export function IfBlock(node, context) {
 	validate_block_not_empty(node.alternate, context);
 
 	if (context.state.analysis.runes) {
-		const parent = context.path.at(-1);
-		const expected =
-			context.path.at(-2)?.type === 'IfBlock' &&
-			parent?.type === 'Fragment' &&
-			parent.nodes.length === 1
-				? ':'
-				: '#';
-
-		validate_opening_tag(node, context.state, expected);
+		validate_opening_tag(node, context.state, node.elseif ? ':' : '#');
 	}
 
 	mark_subtree_dynamic(context.path);

packages/svelte/tests/validator/samples/if-block-whitespace-runes/errors.json

@@ -3,11 +3,11 @@
 		"code": "block_unexpected_character",
 		"message": "Expected a `#` character immediately following the opening bracket",
 		"start": {
-			"line": 5,
+			"line": 10,
 			"column": 1
 		},
 		"end": {
-			"line": 5,
+			"line": 10,
 			"column": 6
 		}
 	}

packages/svelte/tests/validator/samples/if-block-whitespace-runes/input.svelte

@@ -1,5 +1,10 @@
 <svelte:options runes={true} />
 
+<!-- ok -->
+{#if true}{#if true}{/if}{/if}
+{#if foo}{:else if bar}{/if}
+{#if foo}{:else}{/if}
+
 <!-- prettier-ignore -->
 <div>
 	{ #if true}