From cb9c9738293321bf92a52b107917efe07e2e0245 Mon Sep 17 00:00:00 2001
From: Rob Pike <r@golang.org>
Date: Mon, 3 Aug 2009 13:34:20 -0700
Subject: [PATCH] don't crash printing a nil map

R=rsc
DELTA=19  (18 added, 0 deleted, 1 changed)
OCL=32656
CL=32670
---
 src/pkg/fmt/fmt_test.go  | 14 ++++++++++++++
 src/pkg/reflect/value.go |  6 +++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/pkg/fmt/fmt_test.go b/src/pkg/fmt/fmt_test.go
index 5cc887e41de..9d772e1befa 100644
--- a/src/pkg/fmt/fmt_test.go
+++ b/src/pkg/fmt/fmt_test.go
@@ -270,3 +270,17 @@ func TestMapPrinter(t *testing.T) {
 	presentInMap(Sprintf("%v", m1), a, t);
 	presentInMap(Sprint(m1), a, t);
 }
+
+func TestEmptyMap(t *testing.T) {
+	const emptyMapStr = "map[]";
+	var m map[string]int;
+	s := Sprint(m);
+	if s != emptyMapStr {
+		t.Errorf("nil map printed as %q not %q", s, emptyMapStr);
+	}
+	m = make(map[string]int);
+	s = Sprint(m);
+	if s != emptyMapStr {
+		t.Errorf("empty map printed as %q not %q", s, emptyMapStr);
+	}
+}
diff --git a/src/pkg/reflect/value.go b/src/pkg/reflect/value.go
index 4dc130a6cd4..c32574a3f0f 100644
--- a/src/pkg/reflect/value.go
+++ b/src/pkg/reflect/value.go
@@ -1008,8 +1008,12 @@ func (v *MapValue) Len() int {
 func (v *MapValue) Keys() []Value {
 	tk := v.Type().(*MapType).Key();
 	m := *(**byte)(v.addr);
+	mlen := int32(0);
+	if m != nil {
+		mlen = maplen(m)
+	}
 	it := mapiterinit(m);
-	a := make([]Value, maplen(m));
+	a := make([]Value, mlen);
 	var i int;
 	for i = 0; i < len(a); i++ {
 		k := MakeZero(tk);