error on binding to undeclared variable

src/compile/nodes/Binding.ts

@@ -38,6 +38,12 @@ export default class Binding extends Node {
 			});
 		} else {
 			const variable = component.var_lookup.get(name);
+
+			if (!variable) component.error(this.expression.node, {
+				code: 'binding-undeclared',
+				message: `${name} is not declared`
+			});
+
 			variable[this.expression.node.type === 'MemberExpression' ? 'mutated' : 'reassigned'] = true;
 		}
 

test/validator/index.js

@@ -64,11 +64,16 @@ describe("validate", () => {
 					throw new Error(`Expected an error: ${expected.message}`);
 				}
 
-				assert.equal(error.code, expected.code);
+				try {
-				assert.equal(error.message, expected.message);
+					assert.equal(error.code, expected.code);
-				assert.deepEqual(error.start, expected.start);
+					assert.equal(error.message, expected.message);
-				assert.deepEqual(error.end, expected.end);
+					assert.deepEqual(error.start, expected.start);
-				assert.equal(error.pos, expected.pos);
+					assert.deepEqual(error.end, expected.end);
+					assert.equal(error.pos, expected.pos);
+				} catch (e) {
+					console.error(error)
+					throw e;
+				}
 			}
 		});
 	});

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

@@ -0,0 +1,15 @@
+[{
+	"code": "binding-undeclared",
+	"message": "foo is not declared",
+	"pos": 37,
+	"start": {
+		"line": 2,
+		"column": 19,
+		"character": 37
+	},
+	"end": {
+		"line": 2,
+		"column": 22,
+		"character": 40
+	}
+}]

test/validator/samples/binding-invalid-value/input.html

@@ -0,0 +1,2 @@
+<script></script>
+<input bind:value={foo}>