From 63cbe2108ac35204ffc99d16e5a520502ec7ade7 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Sat, 19 Jul 2025 11:35:43 -0700
Subject: [PATCH] fix: disallow `export { foo as default }` in `<script
 module>` (#16447)

* fix: disallow `export { foo as default }` in `<script module>`

* add test

* fix test
---
 .changeset/curly-buttons-burn.md                   |  5 +++++
 .../2-analyze/visitors/ExportNamedDeclaration.js   | 11 +++++++++++
 .../samples/default-export-indirect/errors.json    | 14 ++++++++++++++
 .../samples/default-export-indirect/input.svelte   |  4 ++++
 4 files changed, 34 insertions(+)
 create mode 100644 .changeset/curly-buttons-burn.md
 create mode 100644 packages/svelte/tests/validator/samples/default-export-indirect/errors.json
 create mode 100644 packages/svelte/tests/validator/samples/default-export-indirect/input.svelte

diff --git a/.changeset/curly-buttons-burn.md b/.changeset/curly-buttons-burn.md
new file mode 100644
index 0000000000..f5d45256fa
--- /dev/null
+++ b/.changeset/curly-buttons-burn.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: disallow `export { foo as default }` in `<script module>`
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js
index 4b85894e52..5b8d9ba053 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js
@@ -11,6 +11,17 @@ export function ExportNamedDeclaration(node, context) {
 	// visit children, so bindings are correctly initialised
 	context.next();
 
+	if (
+		context.state.ast_type &&
+		node.specifiers.some((specifier) =>
+			specifier.exported.type === 'Identifier'
+				? specifier.exported.name === 'default'
+				: specifier.exported.value === 'default'
+		)
+	) {
+		e.module_illegal_default_export(node);
+	}
+
 	if (node.declaration?.type === 'VariableDeclaration') {
 		// in runes mode, forbid `export let`
 		if (
diff --git a/packages/svelte/tests/validator/samples/default-export-indirect/errors.json b/packages/svelte/tests/validator/samples/default-export-indirect/errors.json
new file mode 100644
index 0000000000..6a8b2b3c13
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/default-export-indirect/errors.json
@@ -0,0 +1,14 @@
+[
+	{
+		"code": "module_illegal_default_export",
+		"message": "A component cannot have a default export",
+		"start": {
+			"line": 3,
+			"column": 4
+		},
+		"end": {
+			"line": 3,
+			"column": 32
+		}
+	}
+]
diff --git a/packages/svelte/tests/validator/samples/default-export-indirect/input.svelte b/packages/svelte/tests/validator/samples/default-export-indirect/input.svelte
new file mode 100644
index 0000000000..72150edab1
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/default-export-indirect/input.svelte
@@ -0,0 +1,4 @@
+<script module>
+    let answer = 42;
+    export { answer as default};
+</script>
\ No newline at end of file