cmd/gc: disallow fallthrough in final case of switch

Small change to cmd/gc to catch a "fallthrough" in the final case of a switch.

R=golang-dev, rsc, mtj
CC=golang-dev
https://golang.org/cl/7841043

1 files changed, 36 insertions, 0 deletions

diff --git a/test/switch4.go b/test/switch4.go
new file mode 100644
index 0000000000..f38efe68c6
--- /dev/null
+++ b/test/switch4.go
@@ -0,0 +1,36 @@
+// errorcheck
+
+// Copyright 2011 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.
+
+// Verify that erroneous switch statements are detected by the compiler.
+// Does not compile.
+
+package main
+
+type I interface {
+	M()
+}
+
+func bad() {
+
+	i5 := 5
+	switch i5 {
+	case 5:
+		fallthrough // ERROR "cannot fallthrough final case in switch"
+	}
+}
+
+func good() {
+	var i interface{}
+	var s string
+
+	switch i {
+	case s:
+	}
+
+	switch s {
+	case i:
+	}
+}