disallow bindings to global variables (#2295)

src/compile/nodes/Binding.ts

@@ -39,7 +39,7 @@ export default class Binding extends Node {
 		} else {
 			const variable = component.var_lookup.get(name);
 
-			if (!variable) component.error(this.expression.node, {
+			if (!variable || variable.global) component.error(this.expression.node, {
 				code: 'binding-undeclared',
 				message: `${name} is not declared`
 			});

test/validator/samples/binding-invalid-value-global/errors.json

@@ -0,0 +1,15 @@
+[{
+	"code": "binding-undeclared",
+	"message": "foo is not declared",
+	"pos": 58,
+	"start": {
+		"line": 4,
+		"column": 19,
+		"character": 58
+	},
+	"end": {
+		"line": 4,
+		"column": 22,
+		"character": 61
+	}
+}]

test/validator/samples/binding-invalid-value-global/input.svelte

@@ -0,0 +1,4 @@
+<script>
+		console.log(foo);
+</script>
+<input bind:value={foo}>