fix: error when exporting reassigned state from module context (#10728)

fixes #10380

Author: dummdidumm

.changeset/small-sheep-type.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: error when exporting reassigned state from module context

packages/svelte/src/compiler/phases/2-analyze/validation.js

@@ -997,11 +997,29 @@ export const validation_runes = merge(validation, a11y_validators, {
 		if (node.label.name !== '$' || path.at(-1)?.type !== 'Program') return;
 		error(node, 'invalid-legacy-reactive-statement');
 	},
-	ExportNamedDeclaration(node, { state }) {
-		if (node.declaration?.type !== 'VariableDeclaration') return;
-		if (node.declaration.kind !== 'let') return;
-		if (state.analysis.instance.scope !== state.scope) return;
-		error(node, 'invalid-legacy-export');
+	ExportNamedDeclaration(node, { state, next }) {
+		if (state.ast_type === 'module') {
+			if (node.declaration?.type !== 'VariableDeclaration') return;
+
+			// visit children, so bindings are correctly initialised
+			next();
+
+			for (const declarator of node.declaration.declarations) {
+				for (const id of extract_identifiers(declarator.id)) {
+					validate_export(node, state.scope, id.name);
+				}
+			}
+		} else {
+			if (node.declaration?.type !== 'VariableDeclaration') return;
+			if (node.declaration.kind !== 'let') return;
+			if (state.analysis.instance.scope !== state.scope) return;
+			error(node, 'invalid-legacy-export');
+		}
+	},
+	ExportSpecifier(node, { state }) {
+		if (state.ast_type === 'module') {
+			validate_export(node, state.scope, node.local.name);
+		}
 	},
 	CallExpression(node, { state, path }) {
 		validate_call_expression(node, state.scope, path);

packages/svelte/tests/compiler-errors/samples/export-state-module/_config.js

@@ -0,0 +1,10 @@
+import { test } from '../../test';
+
+export default test({
+	error: {
+		code: 'invalid-state-export',
+		message:
+			"Cannot export state from a module if it is reassigned. Either export a function returning the state value or only mutate the state value's properties",
+		position: [76, 114]
+	}
+});

packages/svelte/tests/compiler-errors/samples/export-state-module/main.svelte

@@ -0,0 +1,15 @@
+<script context="module">
+	export const object = $state({
+		ok: true
+	});
+
+	export let primitive = $state('nope');
+
+	export function update_object() {
+		object.ok = !object.ok;
+	}
+
+	export function update_primitive() {
+		primitive = 'yep';
+	}
+</script>