reflect: adjust Value.String to give correct answer for methods

Fixes #7859.

LGTM=r
R=adonovan, r
CC=golang-codereviews
https://golang.org/cl/136710043

src/reflect/all_test.go

@@ -3923,3 +3923,19 @@ func useStack(n int) {
 	var b [1024]byte // makes frame about 1KB
 	useStack(n - 1 + int(b[99]))
 }
+
+type Impl struct{}
+
+func (Impl) f() {}
+
+func TestValueString(t *testing.T) {
+	rv := ValueOf(Impl{})
+	if rv.String() != "<reflect_test.Impl Value>" {
+		t.Errorf("ValueOf(Impl{}).String() = %q, want %q", rv.String(), "<reflect_test.Impl Value>")
+	}
+
+	method := rv.Method(0)
+	if method.String() != "<func() Value>" {
+		t.Errorf("ValueOf(Impl{}).Method(0).String() = %q, want %q", method.String(), "<func() Value>")
+	}
+}

src/reflect/value.go

@@ -1771,7 +1771,7 @@ func (v Value) String() string {
 	}
 	// If you call String on a reflect.Value of other type, it's better to
 	// print something than to panic. Useful in debugging.
-	return "<" + v.typ.String() + " Value>"
+	return "<" + v.Type().String() + " Value>"
 }
 
 // TryRecv attempts to receive a value from the channel v but will not block.