From bec7ca79186cbdbc40b6992b5a6188ad46a3a577 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Wed, 26 Nov 2025 13:25:43 -0800
Subject: [PATCH] fix: throw on invalid `{@tag}`s (#17256)

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

* fix
---
 .changeset/six-lemons-yell.md                            | 5 +++++
 .../docs/98-reference/.generated/compile-errors.md       | 6 ++++++
 packages/svelte/messages/compile-errors/template.md      | 4 ++++
 packages/svelte/src/compiler/errors.js                   | 9 +++++++++
 packages/svelte/src/compiler/phases/1-parse/state/tag.js | 3 +++
 5 files changed, 27 insertions(+)
 create mode 100644 .changeset/six-lemons-yell.md

diff --git a/.changeset/six-lemons-yell.md b/.changeset/six-lemons-yell.md
new file mode 100644
index 0000000000..3931644648
--- /dev/null
+++ b/.changeset/six-lemons-yell.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: throw on invalid `{@tag}`s
diff --git a/documentation/docs/98-reference/.generated/compile-errors.md b/documentation/docs/98-reference/.generated/compile-errors.md
index 94ea46b68a..8a8a10c80b 100644
--- a/documentation/docs/98-reference/.generated/compile-errors.md
+++ b/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
 
 ```
diff --git a/packages/svelte/messages/compile-errors/template.md b/packages/svelte/messages/compile-errors/template.md
index dcec3867ef..db23a2eaa8 100644
--- a/packages/svelte/messages/compile-errors/template.md
+++ b/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%
diff --git a/packages/svelte/src/compiler/errors.js b/packages/svelte/src/compiler/errors.js
index 25304e48c8..d6c2efdfdc 100644
--- a/packages/svelte/src/compiler/errors.js
+++ b/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
diff --git a/packages/svelte/src/compiler/phases/1-parse/state/tag.js b/packages/svelte/src/compiler/phases/1-parse/state/tag.js
index 4ff948e165..e6e083c09d 100644
--- a/packages/svelte/src/compiler/phases/1-parse/state/tag.js
+++ b/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);
 }