From 4b6e0eb4c8c9e9c6e422548d32f3e748cc0b27c6 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 4 Dec 2023 06:42:52 -0500
Subject: [PATCH] fix compiler errors around exported state

---
 packages/svelte/src/compiler/errors.js              |  4 ++--
 .../src/compiler/phases/2-analyze/validation.js     | 10 ++++++++--
 .../samples/export-derived-state/_config.js         |  9 +++++++++
 .../samples/export-derived-state/main.svelte.js     |  3 +++
 .../compiler-errors/samples/export-state/_config.js |  9 +++++++++
 .../samples/export-state/main.svelte.js             | 13 +++++++++++++
 packages/svelte/tests/compiler-errors/test.ts       |  8 ++++++--
 7 files changed, 50 insertions(+), 6 deletions(-)
 create mode 100644 packages/svelte/tests/compiler-errors/samples/export-derived-state/_config.js
 create mode 100644 packages/svelte/tests/compiler-errors/samples/export-derived-state/main.svelte.js
 create mode 100644 packages/svelte/tests/compiler-errors/samples/export-state/_config.js
 create mode 100644 packages/svelte/tests/compiler-errors/samples/export-state/main.svelte.js

diff --git a/packages/svelte/src/compiler/errors.js b/packages/svelte/src/compiler/errors.js
index 700ec21e19..805f8b6b1a 100644
--- a/packages/svelte/src/compiler/errors.js
+++ b/packages/svelte/src/compiler/errors.js
@@ -164,8 +164,8 @@ const runes = {
 	'invalid-legacy-export': () => `Cannot use \`export let\` in runes mode — use $props instead`,
 	/** @param {string} rune */
 	'invalid-rune-usage': (rune) => `Cannot use ${rune} rune in non-runes mode`,
-	/** @param {string} rune */
-	'invalid-rune-export': (rune) => `Cannot export value created with ${rune}`,
+	'invalid-state-export': () => `Cannot export state if it is reassigned`,
+	'invalid-derived-export': () => `Cannot export derived state`,
 	'invalid-props-id': () => `$props() can only be used with an object destructuring pattern`,
 	'invalid-props-pattern': () =>
 		`$props() assignment must not contain nested properties or computed keys`,
diff --git a/packages/svelte/src/compiler/phases/2-analyze/validation.js b/packages/svelte/src/compiler/phases/2-analyze/validation.js
index 99cc8137d6..c41b76ad69 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/validation.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/validation.js
@@ -481,8 +481,14 @@ export const validation_legacy = merge(validation, a11y_validators, {
  */
 function validate_export(node, scope, name) {
 	const binding = scope.get(name);
-	if (binding && (binding.kind === 'derived' || binding.kind === 'state')) {
-		error(node, 'invalid-rune-export', `$${binding.kind}`);
+	if (!binding) return;
+
+	if (binding.kind === 'derived') {
+		error(node, 'invalid-derived-export');
+	}
+
+	if (binding.kind === 'state' && binding.reassigned) {
+		error(node, 'invalid-state-export');
 	}
 }
 
diff --git a/packages/svelte/tests/compiler-errors/samples/export-derived-state/_config.js b/packages/svelte/tests/compiler-errors/samples/export-derived-state/_config.js
new file mode 100644
index 0000000000..1c171d19c0
--- /dev/null
+++ b/packages/svelte/tests/compiler-errors/samples/export-derived-state/_config.js
@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+export default test({
+	error: {
+		code: 'invalid-derived-export',
+		message: 'Cannot export derived state',
+		position: [24, 66]
+	}
+});
diff --git a/packages/svelte/tests/compiler-errors/samples/export-derived-state/main.svelte.js b/packages/svelte/tests/compiler-errors/samples/export-derived-state/main.svelte.js
new file mode 100644
index 0000000000..0906cedf74
--- /dev/null
+++ b/packages/svelte/tests/compiler-errors/samples/export-derived-state/main.svelte.js
@@ -0,0 +1,3 @@
+let count = $state(0);
+
+export const double = $derived(count * 2);
diff --git a/packages/svelte/tests/compiler-errors/samples/export-state/_config.js b/packages/svelte/tests/compiler-errors/samples/export-state/_config.js
new file mode 100644
index 0000000000..5ddb2a859a
--- /dev/null
+++ b/packages/svelte/tests/compiler-errors/samples/export-state/_config.js
@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+export default test({
+	error: {
+		code: 'invalid-state-export',
+		message: 'Cannot export state if it is reassigned',
+		position: [46, 86]
+	}
+});
diff --git a/packages/svelte/tests/compiler-errors/samples/export-state/main.svelte.js b/packages/svelte/tests/compiler-errors/samples/export-state/main.svelte.js
new file mode 100644
index 0000000000..39d9920f7d
--- /dev/null
+++ b/packages/svelte/tests/compiler-errors/samples/export-state/main.svelte.js
@@ -0,0 +1,13 @@
+export const object = $state({
+	ok: true
+});
+
+export const primitive = $state('nope');
+
+export function update_object() {
+	object.ok = !object.ok;
+}
+
+export function update_primitive() {
+	primitive = 'yep';
+}
diff --git a/packages/svelte/tests/compiler-errors/test.ts b/packages/svelte/tests/compiler-errors/test.ts
index b7a76c896f..376e790db6 100644
--- a/packages/svelte/tests/compiler-errors/test.ts
+++ b/packages/svelte/tests/compiler-errors/test.ts
@@ -37,11 +37,11 @@ const { test, run } = suite<CompilerErrorTest>((config, cwd) => {
 		}
 	}
 
-	if (fs.existsSync(`${cwd}/main.js`)) {
+	if (fs.existsSync(`${cwd}/main.svelte.js`)) {
 		let caught_error = false;
 
 		try {
-			compileModule(fs.readFileSync(`${cwd}/main.js`, 'utf-8'), {
+			compileModule(fs.readFileSync(`${cwd}/main.svelte.js`, 'utf-8'), {
 				generate: 'client'
 			});
 		} catch (e) {
@@ -51,6 +51,10 @@ const { test, run } = suite<CompilerErrorTest>((config, cwd) => {
 
 			expect(error.code).toMatch(config.error.code);
 			expect(error.message).toMatch(config.error.message);
+
+			if (config.error.position) {
+				expect(error.position).toEqual(config.error.position);
+			}
 		}
 
 		if (!caught_error) {