From 029457aab54c8c8ae25aaf51725d002aaba8749c Mon Sep 17 00:00:00 2001
From: Robert Griesemer <gri@golang.org>
Date: Wed, 27 Feb 2013 14:24:41 -0800
Subject: [PATCH] go/types: don't crash when assigning to undefined variables

R=adonovan
CC=golang-dev
https://golang.org/cl/7369059
---
 src/pkg/go/types/stmt.go            | 4 ++++
 src/pkg/go/types/testdata/stmt0.src | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/src/pkg/go/types/stmt.go b/src/pkg/go/types/stmt.go
index 730b0608ee..65b12a01ef 100644
--- a/src/pkg/go/types/stmt.go
+++ b/src/pkg/go/types/stmt.go
@@ -62,6 +62,10 @@ func (check *checker) assign1to1(lhs, rhs ast.Expr, x *operand, decl bool, iota
 			}
 		}
 
+		if x.mode == invalid || z.mode == invalid {
+			return
+		}
+
 		check.assignOperand(&z, x)
 		if x.mode != invalid && z.mode == constant {
 			check.errorf(x.pos(), "cannot assign %s to %s", x, &z)
diff --git a/src/pkg/go/types/testdata/stmt0.src b/src/pkg/go/types/testdata/stmt0.src
index 37610d3ddd..d4e08f6c0d 100644
--- a/src/pkg/go/types/testdata/stmt0.src
+++ b/src/pkg/go/types/testdata/stmt0.src
@@ -32,6 +32,8 @@ func _() {
 
 	var u64 uint64
 	u64 += 1<<u64
+
+	undeclared /* ERROR "undeclared" */ = 991
 }
 
 func _incdecs() {
-- 
2.48.1