cmd/gc: print x++ (not x += 1) in errors about x++

Fixes #8311.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews, r
https://golang.org/cl/146270043

1 files changed, 16 insertions, 0 deletions

diff --git a/test/fixedbugs/issue8311.go b/test/fixedbugs/issue8311.go
new file mode 100644
index 0000000000..dd928566d6
--- /dev/null
+++ b/test/fixedbugs/issue8311.go
@@ -0,0 +1,16 @@
+// 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.
+
+// issue 8311.
+// error for x++ should say x++ not x += 1
+
+package p
+
+func f() {
+	var x []byte
+	x++ // ERROR "invalid operation: x[+][+]"
+
+}