From 59847321a7c3f1b3398667b0923916307ab829d7 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Fri, 21 Feb 2014 13:51:22 -0500
Subject: [PATCH] reflect: better error for walking through nil embedded struct
 pointer

The old error was "call of reflect.Value.Field on ptr Value".

http://play.golang.org/p/Zm-ZbQaPeR

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/67020043
---
 src/pkg/reflect/all_test.go | 24 ++++++++++++++++++++++++
 src/pkg/reflect/value.go    |  5 ++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/pkg/reflect/all_test.go b/src/pkg/reflect/all_test.go
index 23e4e235f2..c1f95d6049 100644
--- a/src/pkg/reflect/all_test.go
+++ b/src/pkg/reflect/all_test.go
@@ -15,6 +15,7 @@ import (
 	. "reflect"
 	"runtime"
 	"sort"
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -3692,3 +3693,26 @@ func TestBigZero(t *testing.T) {
 		}
 	}
 }
+
+func TestFieldByIndexNil(t *testing.T) {
+	type P struct {
+		F int
+	}
+	type T struct {
+		*P
+	}
+	v := ValueOf(T{})
+
+	v.FieldByName("P") // should be fine
+
+	defer func() {
+		if err := recover(); err == nil {
+			t.Fatalf("no error")
+		} else if !strings.Contains(fmt.Sprint(err), "nil pointer to embedded struct") {
+			t.Fatalf(`err=%q, wanted error containing "nil pointer to embedded struct"`, err)
+		}
+	}()
+	v.FieldByName("F") // should panic
+
+	t.Fatalf("did not panic")
+}
diff --git a/src/pkg/reflect/value.go b/src/pkg/reflect/value.go
index 1edb1f0465..fba0e1ef68 100644
--- a/src/pkg/reflect/value.go
+++ b/src/pkg/reflect/value.go
@@ -889,7 +889,10 @@ func (v Value) FieldByIndex(index []int) Value {
 	v.mustBe(Struct)
 	for i, x := range index {
 		if i > 0 {
-			if v.Kind() == Ptr && v.Elem().Kind() == Struct {
+			if v.Kind() == Ptr && v.typ.Elem().Kind() == Struct {
+				if v.IsNil() {
+					panic("reflect: indirection through nil pointer to embedded struct")
+				}
 				v = v.Elem()
 			}
 		}