From: Brad Fitzpatrick <bradfitz@golang.org>
Date: Fri, 29 Apr 2016 03:04:30 +0000 (-0500)
Subject: context: produce a nicer panic message for a nil WithValue key
X-Git-Tag: go1.7beta1~412
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=c884f6594a594d2d18c4d21106592bd3cdfcbe9b;p=gostls13.git

context: produce a nicer panic message for a nil WithValue key

Change-Id: I2e8ae403622ba7131cadaba506100d79613183f1
Reviewed-on: https://go-review.googlesource.com/22601
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>
---

diff --git a/src/context/context.go b/src/context/context.go
index da294b1292..5184b94e51 100644
--- a/src/context/context.go
+++ b/src/context/context.go
@@ -428,6 +428,9 @@ func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
 //
 // The provided key must be comparable.
 func WithValue(parent Context, key, val interface{}) Context {
+	if key == nil {
+		panic("nil key")
+	}
 	if !reflect.TypeOf(key).Comparable() {
 		panic("key is not comparable")
 	}
diff --git a/src/context/context_test.go b/src/context/context_test.go
index aa26161d2b..99456b188d 100644
--- a/src/context/context_test.go
+++ b/src/context/context_test.go
@@ -583,6 +583,10 @@ func TestWithValueChecksKey(t *testing.T) {
 	if panicVal == nil {
 		t.Error("expected panic")
 	}
+	panicVal = recoveredValue(func() { WithValue(Background(), nil, "bar") })
+	if got, want := fmt.Sprint(panicVal), "nil key"; got != want {
+		t.Errorf("panic = %q; want %q", got, want)
+	}
 }
 
 func recoveredValue(fn func()) (v interface{}) {