From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Mon, 30 May 2016 23:42:38 +0000 (-0700)
Subject: cmd/compile: disallow multiple nil cases in a type switch
X-Git-Tag: go1.7beta1~31
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=0e13dbc1a91cbe00e3c83a55f56db69380fe8f68;p=gostls13.git

cmd/compile: disallow multiple nil cases in a type switch

Fixes #15898.

Change-Id: I66e2ad21f283563c7142aa820f0354711d964768
Reviewed-on: https://go-review.googlesource.com/23573
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
---

diff --git a/src/cmd/compile/internal/gc/swt.go b/src/cmd/compile/internal/gc/swt.go
index aac92fd311..4940c97a90 100644
--- a/src/cmd/compile/internal/gc/swt.go
+++ b/src/cmd/compile/internal/gc/swt.go
@@ -104,7 +104,7 @@ func typecheckswitch(n *Node) {
 
 	n.Type = t
 
-	var def *Node
+	var def, niltype *Node
 	for _, ncase := range n.List.Slice() {
 		setlineno(n)
 		if ncase.List.Len() == 0 {
@@ -150,6 +150,12 @@ func typecheckswitch(n *Node) {
 					var ptr int
 					switch {
 					case n1.Op == OLITERAL && n1.Type.IsKind(TNIL):
+						// case nil:
+						if niltype != nil {
+							Yyerror("multiple nil cases in type switch (first at %v)", niltype.Line())
+						} else {
+							niltype = ncase
+						}
 					case n1.Op != OTYPE && n1.Type != nil: // should this be ||?
 						Yyerror("%v is not a type", Nconv(n1, FmtLong))
 						// reset to original type
diff --git a/test/fixedbugs/issue15898.go b/test/fixedbugs/issue15898.go
new file mode 100644
index 0000000000..7b66ea23dc
--- /dev/null
+++ b/test/fixedbugs/issue15898.go
@@ -0,0 +1,18 @@
+// errorcheck
+
+// Copyright 2016 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 p
+
+func f(e interface{}) {
+	switch e.(type) {
+	case nil, nil: // ERROR "multiple nil cases in type switch"
+	}
+
+	switch e.(type) {
+	case nil:
+	case nil: // ERROR "multiple nil cases in type switch"
+	}
+}