From 4e65478cbd9691aefdcf0c2f636d4909c8a45993 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Mon, 14 Nov 2011 16:11:15 -0500
Subject: [PATCH] reflect: empty slice/map is not DeepEqual to nil

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5373095
---
 src/pkg/reflect/all_test.go  | 8 ++++++++
 src/pkg/reflect/deepequal.go | 6 ++++++
 2 files changed, 14 insertions(+)

diff --git a/src/pkg/reflect/all_test.go b/src/pkg/reflect/all_test.go
index 271a651147..2f6917d3c6 100644
--- a/src/pkg/reflect/all_test.go
+++ b/src/pkg/reflect/all_test.go
@@ -651,6 +651,14 @@ var deepEqualTests = []DeepEqualTest{
 	{nil, 1, false},
 	{1, nil, false},
 
+	// Nil vs empty: not the same.
+	{[]int{}, []int(nil), false},
+	{[]int{}, []int{}, true},
+	{[]int(nil), []int(nil), true},
+	{map[int]int{}, map[int]int(nil), false},
+	{map[int]int{}, map[int]int{}, true},
+	{map[int]int(nil), map[int]int(nil), true},
+
 	// Mismatched types
 	{1, 1.0, false},
 	{int32(1), int64(1), false},
diff --git a/src/pkg/reflect/deepequal.go b/src/pkg/reflect/deepequal.go
index 63c28fe202..df5ec0a609 100644
--- a/src/pkg/reflect/deepequal.go
+++ b/src/pkg/reflect/deepequal.go
@@ -69,6 +69,9 @@ func deepValueEqual(v1, v2 Value, visited map[uintptr]*visit, depth int) (b bool
 		}
 		return true
 	case Slice:
+		if v1.IsNil() != v2.IsNil() {
+			return false
+		}
 		if v1.Len() != v2.Len() {
 			return false
 		}
@@ -93,6 +96,9 @@ func deepValueEqual(v1, v2 Value, visited map[uintptr]*visit, depth int) (b bool
 		}
 		return true
 	case Map:
+		if v1.IsNil() != v2.IsNil() {
+			return false
+		}
 		if v1.Len() != v2.Len() {
 			return false
 		}
-- 
2.50.0