Sub inerits from automaticEnvApplied and envKeyReplacer

parents are tracked so sub(x).sub(y).GetString(z) looks up x.y.z

viper.go

@@ -206,6 +206,7 @@ type Viper struct {
 	envKeyReplacer      StringReplacer
 	allowEmptyEnv       bool
 
+	parents        []string
 	config         map[string]interface{}
 	override       map[string]interface{}
 	defaults       map[string]interface{}
@@ -232,6 +233,7 @@ func New() *Viper {
 	v.configPermissions = os.FileMode(0o644)
 	v.fs = afero.NewOsFs()
 	v.config = make(map[string]interface{})
+	v.parents = []string{}
 	v.override = make(map[string]interface{})
 	v.defaults = make(map[string]interface{})
 	v.kvstore = make(map[string]interface{})
@@ -948,6 +950,9 @@ func (v *Viper) Sub(key string) *Viper {
 	}
 
 	if reflect.TypeOf(data).Kind() == reflect.Map {
+		subv.parents = append(v.parents, strings.ToLower(key))
+		subv.automaticEnvApplied = v.automaticEnvApplied
+		subv.envKeyReplacer = v.envKeyReplacer
 		subv.config = cast.ToStringMap(data)
 		return subv
 	}
@@ -1294,9 +1299,10 @@ func (v *Viper) find(lcaseKey string, flagDefault bool) interface{} {
 
 	// Env override next
 	if v.automaticEnvApplied {
+		envKey := strings.Join(append(v.parents, lcaseKey), ".")
 		// even if it hasn't been registered, if automaticEnv is used,
 		// check any Get request
-		if val, ok := v.getEnv(v.mergeWithEnvPrefix(lcaseKey)); ok {
+		if val, ok := v.getEnv(v.mergeWithEnvPrefix(envKey)); ok {
 			return val
 		}
 		if nested && v.isPathShadowedInAutoEnv(path) != "" {

viper_test.go

@@ -733,6 +733,19 @@ func TestEnvKeyReplacer(t *testing.T) {
 	assert.Equal(t, "30s", v.Get("refresh-interval"))
 }
 
+func TestEnvSubConfig(t *testing.T) {
+	initYAML()
+
+	v.AutomaticEnv()
+
+	replacer := strings.NewReplacer(".", "_")
+	v.SetEnvKeyReplacer(replacer)
+
+	testutil.Setenv(t, "CLOTHING_PANTS_SIZE", "small")
+	subv := v.Sub("clothing").Sub("pants")
+	assert.Equal(t, "small", subv.Get("size"))
+}
+
 func TestAllKeys(t *testing.T) {
 	initConfigs()
 
@@ -1522,6 +1535,14 @@ func TestSub(t *testing.T) {
 
 	subv = v.Sub("missing.key")
 	assert.Equal(t, (*Viper)(nil), subv)
+
+	subv = v.Sub("clothing")
+	assert.Equal(t, subv.parents[0], "clothing")
+
+	subv = v.Sub("clothing").Sub("pants")
+	assert.Equal(t, len(subv.parents), 2)
+	assert.Equal(t, subv.parents[0], "clothing")
+	assert.Equal(t, subv.parents[1], "pants")
 }
 
 var hclWriteExpected = []byte(`"foos" = {