Change implementation of find sub-tree to work with deep trees

* The previous implementation had an issue with nested structures deeper
  than one level. It would copy keys over instead of the expected object
  structure. In the example in this commit, UnmarshalKey("clothing") was
  returning "pants.size":"35" instead of "pants"{"size":"35"}

viper.go

@@ -1009,9 +1009,15 @@ func (v *Viper) find(lcaseKey string, flagDefault bool) interface{} {
 	// it could also be a key prefix, search for that prefix to get the values from
 	// pflags that match it
 	sub := make(map[string]interface{})
-	for key, val := range v.pflags {
-		if flagDefault && strings.HasPrefix(key, lcaseKey) {
-			sub[strings.TrimPrefix(key, lcaseKey+".")] = val.ValueString()
+	for _, key := range v.AllKeys() {
+		if strings.HasPrefix(key, lcaseKey) {
+			value := v.Get(key)
+			keypath := strings.Split(lcaseKey, v.keyDelim)
+			path := strings.Split(key, v.keyDelim)[len(keypath)-1:]
+			lastKey := strings.ToLower(path[len(path)-1])
+			deepestMap := deepSearch(sub, path[1:len(path)-1])
+			// set innermost value
+			deepestMap[lastKey] = value
 		}
 	}
 	if len(sub) != 0 {

viper_test.go

@@ -875,7 +875,49 @@ func TestSubPflags(t *testing.T) {
 	v.BindPFlag("eyes", &pflag.Flag{Value: newStringValue("brown"), Changed: true})
 	v.BindPFlag("beard", &pflag.Flag{Value: newStringValue("yes"), Changed: true})
 
+	type pants struct {
+		Size string
+	}
+
+	type clothing struct {
+		Jacket   string
+		Trousers string
+		Pants    pants
+	}
+
+	type cfg struct {
+		Name     string
+		Clothing clothing
+		Age      int
+		Eyes     string
+		Beard    bool
+	}
+
+	var c cfg
+	v.Unmarshal(&c)
+	assert.Equal(t, v.Get("name"), c.Name)
+	assert.Equal(t, v.Get("clothing.jacket"), c.Clothing.Jacket)
+	assert.Equal(t, v.Get("clothing.trousers"), c.Clothing.Trousers)
+	assert.Equal(t, v.Get("clothing.pants.size"), c.Clothing.Pants.Size)
+	assert.Equal(t, v.GetInt("age"), c.Age)
+	assert.Equal(t, v.Get("eyes"), c.Eyes)
+	assert.Equal(t, v.GetBool("beard"), c.Beard)
+
+	var cloth clothing
+	v.UnmarshalKey("clothing", &cloth)
+	assert.Equal(t, c.Clothing, cloth)
+
+	var p pants
+	v.UnmarshalKey("clothing.pants", &p)
+	assert.Equal(t, c.Clothing.Pants, p)
+
+	var size string
+	v.UnmarshalKey("clothing.pants.size", &size)
+	assert.Equal(t, c.Clothing.Pants.Size, size)
+
 	subv := v.Sub("clothing")
+	assert.Equal(t, v.Get("clothing.jacket"), subv.Get("jacket"))
+	assert.Equal(t, v.Get("clothing.trousers"), subv.Get("trousers"))
 	assert.Equal(t, v.Get("clothing.pants.size"), subv.Get("pants.size"))
 
 	subv = v.Sub("clothing.pants")