fix: require whitespace after @const tag (#11379)

Author: jrmajor

.changeset/six-boats-shave.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: require whitespace after `@const` tag

packages/svelte/src/compiler/phases/1-parse/state/tag.js

@@ -543,7 +543,7 @@ function special(parser) {
 	}
 
 	if (parser.eat('const')) {
-		parser.allow_whitespace();
+		parser.require_whitespace();
 
 		const id = read_pattern(parser);
 		parser.allow_whitespace();

packages/svelte/tests/compiler-errors/samples/const-tag-whitespace/_config.js

@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+export default test({
+	error: {
+		code: 'expected_whitespace',
+		message: 'Expected whitespace',
+		position: [19, 19]
+	}
+});

packages/svelte/tests/compiler-errors/samples/const-tag-whitespace/main.svelte

@@ -0,0 +1,3 @@
+{#if true}
+	{@constfoo = 'bar'}
+{/if}