From daea2aaa5a9722ef6afe3430f5a3b0edfa3464e4 Mon Sep 17 00:00:00 2001
From: Roy Razon <royr@gett.com>
Date: Tue, 16 Jan 2018 17:03:31 +0200
Subject: [PATCH] Creation of Sub now copies parent properties and sets
 envPrefix

---
 viper.go      | 19 +++++++++++++++++--
 viper_test.go | 16 ++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/viper.go b/viper.go
index ad8a037..960f13d 100644
--- a/viper.go
+++ b/viper.go
@@ -204,6 +204,13 @@ func New() *Viper {
 	return v
 }
 
+func newFrom(from *Viper) *Viper {
+	v := *new(Viper)
+	v = *from // shallow clone
+
+	return &v
+}
+
 // Intended for testing, will reset all to default settings.
 // In the public interface for the viper package so applications
 // can use it in their testing as well.
@@ -647,11 +654,19 @@ func (v *Viper) Get(key string) interface{} {
 	return val
 }
 
+func (v *Viper) prefixOfSub(key string) string {
+	if v.envPrefix == "" {
+		return key
+	} else {
+		return v.envPrefix + "." + key
+	}
+}
+
 // Sub returns new Viper instance representing a sub tree of this instance.
 // Sub is case-insensitive for a key.
 func Sub(key string) *Viper { return v.Sub(key) }
 func (v *Viper) Sub(key string) *Viper {
-	subv := New()
+	subv := newFrom(v)
 	data := v.Get(key)
 	if data == nil {
 		return nil
@@ -659,6 +674,7 @@ func (v *Viper) Sub(key string) *Viper {
 
 	if reflect.TypeOf(data).Kind() == reflect.Map {
 		subv.config = cast.ToStringMap(data)
+		subv.envPrefix = v.prefixOfSub(key)
 		return subv
 	}
 	return nil
@@ -882,7 +898,6 @@ func (v *Viper) BindEnv(input ...string) error {
 // Viper will check to see if an alias exists first.
 // Note: this assumes a lower-cased key given.
 func (v *Viper) find(lcaseKey string) interface{} {
-
 	var (
 		val    interface{}
 		exists bool
diff --git a/viper_test.go b/viper_test.go
index c93480e..d98180e 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -848,6 +848,22 @@ func TestSub(t *testing.T) {
 	assert.Equal(t, (*Viper)(nil), subv)
 }
 
+func TestSubEnv(t *testing.T) {
+	v := New()
+	v.SetConfigType("yaml")
+	v.ReadConfig(bytes.NewBuffer(yamlExample))
+	v.AutomaticEnv()
+	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
+
+	assert.Equal(t, "leather", v.GetString("clothing.jacket"))
+	subv := v.Sub("clothing")
+	assert.Equal(t, "leather", subv.GetString("jacket"))
+
+	os.Setenv("CLOTHING_JACKET", "13")
+	assert.Equal(t, "13", v.GetString("clothing.jacket"))
+	assert.Equal(t, "13", subv.GetString("jacket"))
+}
+
 var hclWriteExpected = []byte(`"foos" = {
   "foo" = {
     "key" = 1