From ede1edd314452a1bfd729503e990cf06e04da641 Mon Sep 17 00:00:00 2001
From: Rich Harris <richard.a.harris@gmail.com>
Date: Thu, 16 Nov 2023 17:18:04 -0500
Subject: [PATCH] fix: emit useful error on invalid binding to derived state
 (#9497)

closes #9495
---
 .changeset/clean-eels-beg.md                              | 5 +++++
 packages/svelte/src/compiler/errors.js                    | 1 +
 .../svelte/src/compiler/phases/2-analyze/validation.js    | 4 ++++
 .../samples/runes-no-derived-binding/_config.js           | 8 ++++++++
 .../samples/runes-no-derived-binding/main.svelte          | 6 ++++++
 5 files changed, 24 insertions(+)
 create mode 100644 .changeset/clean-eels-beg.md
 create mode 100644 packages/svelte/tests/compiler-errors/samples/runes-no-derived-binding/_config.js
 create mode 100644 packages/svelte/tests/compiler-errors/samples/runes-no-derived-binding/main.svelte

diff --git a/.changeset/clean-eels-beg.md b/.changeset/clean-eels-beg.md
new file mode 100644
index 000000000000..2cf079196c74
--- /dev/null
+++ b/.changeset/clean-eels-beg.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: emit useful error on invalid binding to derived state
diff --git a/packages/svelte/src/compiler/errors.js b/packages/svelte/src/compiler/errors.js
index 615123088f0f..700ec21e19e0 100644
--- a/packages/svelte/src/compiler/errors.js
+++ b/packages/svelte/src/compiler/errors.js
@@ -187,6 +187,7 @@ const runes = {
 				: ''
 		}`,
 	'invalid-derived-assignment': () => `Invalid assignment to derived state`,
+	'invalid-derived-binding': () => `Invalid binding to derived state`,
 	/**
 	 * @param {string} rune
 	 * @param {number[]} args
diff --git a/packages/svelte/src/compiler/phases/2-analyze/validation.js b/packages/svelte/src/compiler/phases/2-analyze/validation.js
index 34be46269f98..8c6c3365b003 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/validation.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/validation.js
@@ -274,6 +274,10 @@ export const validation = {
 				error(node.expression, 'invalid-binding-value');
 			}
 
+			if (binding.kind === 'derived') {
+				error(node.expression, 'invalid-derived-binding');
+			}
+
 			// TODO handle mutations of non-state/props in runes mode
 		}
 
diff --git a/packages/svelte/tests/compiler-errors/samples/runes-no-derived-binding/_config.js b/packages/svelte/tests/compiler-errors/samples/runes-no-derived-binding/_config.js
new file mode 100644
index 000000000000..3a27b1f9bdac
--- /dev/null
+++ b/packages/svelte/tests/compiler-errors/samples/runes-no-derived-binding/_config.js
@@ -0,0 +1,8 @@
+import { test } from '../../test';
+
+export default test({
+	error: {
+		code: 'invalid-derived-binding',
+		message: 'Invalid binding to derived state'
+	}
+});
diff --git a/packages/svelte/tests/compiler-errors/samples/runes-no-derived-binding/main.svelte b/packages/svelte/tests/compiler-errors/samples/runes-no-derived-binding/main.svelte
new file mode 100644
index 000000000000..6c198dc068fe
--- /dev/null
+++ b/packages/svelte/tests/compiler-errors/samples/runes-no-derived-binding/main.svelte
@@ -0,0 +1,6 @@
+<script>
+	let a = $state(0);
+	let b = $derived({ a });
+</script>
+
+<input type="number" bind:value={b} />