From e06a900b2331e70f8b057dcbd36f6bd304f4c7dc Mon Sep 17 00:00:00 2001
From: vlasy <vlasy@users.noreply.github.com>
Date: Sat, 14 Mar 2020 21:15:37 +0100
Subject: [PATCH] throw compiler error when binding directly to const variables
 (#4506)

---
 src/compiler/compile/nodes/Binding.ts             |  5 +++++
 .../samples/binding-const-field/errors.json       |  1 +
 .../samples/binding-const-field/input.svelte      |  7 +++++++
 test/validator/samples/binding-const/errors.json  | 15 +++++++++++++++
 test/validator/samples/binding-const/input.svelte |  5 +++++
 5 files changed, 33 insertions(+)
 create mode 100644 test/validator/samples/binding-const-field/errors.json
 create mode 100644 test/validator/samples/binding-const-field/input.svelte
 create mode 100644 test/validator/samples/binding-const/errors.json
 create mode 100644 test/validator/samples/binding-const/input.svelte

diff --git a/src/compiler/compile/nodes/Binding.ts b/src/compiler/compile/nodes/Binding.ts
index 7d6fad0a81..2f199709c8 100644
--- a/src/compiler/compile/nodes/Binding.ts
+++ b/src/compiler/compile/nodes/Binding.ts
@@ -72,6 +72,11 @@ export default class Binding extends Node {
 			});
 
 			variable[this.expression.node.type === 'MemberExpression' ? 'mutated' : 'reassigned'] = true;
+
+			if (info.expression.type === 'Identifier' && !variable.writable) component.error(this.expression.node, {
+				code: 'invalid-binding',
+				message: 'Cannot bind to a variable which is not writable',
+			});
 		}
 
 		const type = parent.get_static_attribute_value('type');
diff --git a/test/validator/samples/binding-const-field/errors.json b/test/validator/samples/binding-const-field/errors.json
new file mode 100644
index 0000000000..fe51488c70
--- /dev/null
+++ b/test/validator/samples/binding-const-field/errors.json
@@ -0,0 +1 @@
+[]
diff --git a/test/validator/samples/binding-const-field/input.svelte b/test/validator/samples/binding-const-field/input.svelte
new file mode 100644
index 0000000000..055a16438d
--- /dev/null
+++ b/test/validator/samples/binding-const-field/input.svelte
@@ -0,0 +1,7 @@
+<script>
+	const dummy = {
+		foo: 'bar'
+	};
+</script>
+
+<input bind:value={dummy.foo}>
diff --git a/test/validator/samples/binding-const/errors.json b/test/validator/samples/binding-const/errors.json
new file mode 100644
index 0000000000..6d48af9c4e
--- /dev/null
+++ b/test/validator/samples/binding-const/errors.json
@@ -0,0 +1,15 @@
+[{
+	"code": "invalid-binding",
+	"message": "Cannot bind to a variable which is not writable",
+	"pos": 61,
+	"start": {
+		"line": 5,
+		"column": 19,
+		"character": 61
+	},
+	"end": {
+		"line": 5,
+		"column": 24,
+		"character": 66
+	}
+}]
\ No newline at end of file
diff --git a/test/validator/samples/binding-const/input.svelte b/test/validator/samples/binding-const/input.svelte
new file mode 100644
index 0000000000..1857a1932c
--- /dev/null
+++ b/test/validator/samples/binding-const/input.svelte
@@ -0,0 +1,5 @@
+<script>
+	const dummy = 'foo';
+</script>
+
+<input bind:value={dummy}>