From f2e94b58a01389cb9dcf51821b96435343594879 Mon Sep 17 00:00:00 2001
From: Daniel Morsing <daniel.morsing@gmail.com>
Date: Fri, 3 Jan 2014 21:03:20 +0100
Subject: [PATCH] cmd/gc: silence assignment errors to undefined symbols

Fixes #6406.

R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/46900043
---
 src/cmd/gc/typecheck.c      |  5 +++++
 test/fixedbugs/issue6406.go | 12 ++++++++++++
 test/typecheck.go           |  2 +-
 3 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 test/fixedbugs/issue6406.go

diff --git a/src/cmd/gc/typecheck.c b/src/cmd/gc/typecheck.c
index 31a2f2c5cb..6f8b6adbbf 100644
--- a/src/cmd/gc/typecheck.c
+++ b/src/cmd/gc/typecheck.c
@@ -2680,6 +2680,11 @@ checkassign(Node *n)
 		n->etype = 1;
 		return;
 	}
+
+	// have already complained about n being undefined
+	if(n->op == ONONAME)
+		return;
+
 	yyerror("cannot assign to %N", n);
 }
 
diff --git a/test/fixedbugs/issue6406.go b/test/fixedbugs/issue6406.go
new file mode 100644
index 0000000000..5491193ef3
--- /dev/null
+++ b/test/fixedbugs/issue6406.go
@@ -0,0 +1,12 @@
+// errorcheck
+
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func main() {
+	s = "bob" // ERROR "undefined.*s"
+	_ = s // ERROR "undefined.*s"
+}
diff --git a/test/typecheck.go b/test/typecheck.go
index a2ad91ff4c..6f1204289a 100644
--- a/test/typecheck.go
+++ b/test/typecheck.go
@@ -14,5 +14,5 @@ func mine(int b) int {	// ERROR "undefined.*b"
 
 func main() {
 	mine()		// GCCGO_ERROR "not enough arguments"
-	c = mine()	// ERROR "undefined.*c|not enough arguments" "cannot assign to c"
+	c = mine()	// ERROR "undefined.*c|not enough arguments"
 }
-- 
2.48.1