Add decoder opts to unmarshal exact

Author: sagikazarmark

viper.go

@@ -949,9 +949,11 @@ func decode(input interface{}, config *mapstructure.DecoderConfig) error {
 
 // UnmarshalExact unmarshals the config into a Struct, erroring if a field is nonexistent
 // in the destination struct.
-func UnmarshalExact(rawVal interface{}) error { return v.UnmarshalExact(rawVal) }
-func (v *Viper) UnmarshalExact(rawVal interface{}) error {
-	config := defaultDecoderConfig(rawVal)
+func UnmarshalExact(rawVal interface{}, opts ...DecoderConfigOption) error {
+	return v.UnmarshalExact(rawVal, opts...)
+}
+func (v *Viper) UnmarshalExact(rawVal interface{}, opts ...DecoderConfigOption) error {
+	config := defaultDecoderConfig(rawVal, opts...)
 	config.ErrorUnused = true
 
 	err := decode(v.AllSettings(), config)