fix: throw on invalid `{@tag}`s (#17256)

* fix: throw on invalid `{@tag}`s

* fix

.changeset/six-lemons-yell.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: throw on invalid `{@tag}`s

documentation/docs/98-reference/.generated/compile-errors.md

@@ -525,6 +525,12 @@ Expected an identifier
 Expected identifier or destructure pattern
 ```
 
+### expected_tag
+
+```
+Expected 'html', 'render', 'attach', 'const', or 'debug'
+```
+
 ### expected_token
 
 ```

packages/svelte/messages/compile-errors/template.md

@@ -223,6 +223,10 @@ The same applies to components:
 
 > Expected identifier or destructure pattern
 
+## expected_tag
+
+> Expected 'html', 'render', 'attach', 'const', or 'debug'
+
 ## expected_token
 
 > Expected token %token%

packages/svelte/src/compiler/errors.js

@@ -1129,6 +1129,15 @@ export function expected_pattern(node) {
 	e(node, 'expected_pattern', `Expected identifier or destructure pattern\nhttps://svelte.dev/e/expected_pattern`);
 }
 
+/**
+ * Expected 'html', 'render', 'attach', 'const', or 'debug'
+ * @param {null | number | NodeLike} node
+ * @returns {never}
+ */
+export function expected_tag(node) {
+	e(node, 'expected_tag', `Expected 'html', 'render', 'attach', 'const', or 'debug'\nhttps://svelte.dev/e/expected_tag`);
+}
+
 /**
  * Expected token %token%
  * @param {null | number | NodeLike} node

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

@@ -724,6 +724,7 @@ function special(parser) {
 				expression: new ExpressionMetadata()
 			}
 		});
+		return;
 	}
 
 	if (parser.eat('render')) {
@@ -755,5 +756,7 @@ function special(parser) {
 				snippets: new Set()
 			}
 		});
+		return;
 	}
+	e.expected_tag(parser.index);
 }