fix unmarshal error when the tag contains omitempty (#15)

* fix unmarshal error when the tag contains omitempty

enviper.go

@@ -85,9 +85,22 @@ func (e *Enviper) bindEnvs(in interface{}, prev ...string) {
 		t := ifv.Type().Field(i)
 		tv, ok := t.Tag.Lookup(e.TagName())
 		if ok {
-			if tv == ",squash" {
-				e.bindEnvs(fv.Interface(), prev...)
-				continue
+			if index := strings.Index(tv, ","); index != -1 {
+				if tv[:index] == "-" {
+					continue
+				}
+
+				// If "squash" is specified in the tag, we squash the field down.
+				if strings.Index(tv[index+1:], "squash") != -1 {
+					e.bindEnvs(fv.Interface(), prev...)
+					continue
+				}
+
+				tv = tv[:index]
+			}
+
+			if tv == "" {
+				tv = t.Name
 			}
 		} else {
 			tv = t.Name

enviper_test.go

@@ -59,6 +59,20 @@ func (s *UnmarshalSuite) TestOnlyEnvsByCustomTag() {
 	s.Equal("imTheValueByCustomTag", c.TagTest)
 }
 
+func (s *UnmarshalSuite) TestOnlyEnvsWithTagValue() {
+	s.setupEnvConfig()
+	defer s.tearDownEnvConfig()
+
+	var c Config
+	e := enviper.New(s.v)
+	e.SetEnvPrefix("PREF")
+	s.Nil(e.Unmarshal(&c))
+
+	s.Equal("imTheValueWithOmitempty", c.TagValueWithOmitempty)
+	s.Equal("imTheValueWithCustomName", c.TagValueWithNameOmitempty)
+	s.Equal("", c.TagValueWithDash)
+}
+
 func (s *UnmarshalSuite) TestOnlyEnvs() {
 	s.setupEnvConfig()
 	defer s.tearDownEnvConfig()
@@ -166,8 +180,11 @@ type Config struct {
 	QuxMap map[string]struct {
 		Quuux bool
 	}
-	QUX     `mapstructure:",squash"`
-	TagTest string `custom_tag:"TAG_TEST"`
+	QUX                       `mapstructure:",squash"`
+	TagTest                   string `custom_tag:"TAG_TEST"`
+	TagValueWithOmitempty     string `mapstructure:",omitempty"`
+	TagValueWithNameOmitempty string `mapstructure:"tag_custom_name,omitempty"`
+	TagValueWithDash          string `mapstructure:"-"`
 }
 
 type QUX struct {

fixture_env

@@ -4,3 +4,6 @@ PREF_QUUUX=false
 PREF_QUXMAP_KEY1_QUUUX=true
 PREF_QUUUX_PTR_UNSET_VALUE=testptr3
 PREF_TAG_TEST=imTheValueByCustomTag
+PREF_TAGVALUEWITHOMITEMPTY=imTheValueWithOmitempty
+PREF_TAG_CUSTOM_NAME=imTheValueWithCustomName
+PREF_TAGVALUEWITHDASH=imTheValueWithDash