add Format method to decoders (#79)

aconfig.go

@@ -93,6 +93,7 @@ type Config struct {
 
 // FileDecoder is used to read config from files. See aconfig submodules.
 type FileDecoder interface {
+	Format() string
 	DecodeFile(filename string) (map[string]interface{}, error)
 }
 
@@ -142,9 +143,6 @@ func (l *Loader) init() {
 		}
 		l.config.FileDecoders[".json"] = &jsonDecoder{}
 	}
-	if dec, ok := l.config.FileDecoders[".yaml"]; ok {
-		l.config.FileDecoders[".yml"] = dec
-	}
 
 	if l.config.Args == nil {
 		l.config.Args = os.Args[1:]
@@ -292,7 +290,7 @@ func (l *Loader) loadFromFile() error {
 			return err
 		}
 
-		tag := getTagForExt(ext)
+		tag := decoder.Format()
 
 		for _, field := range l.fields {
 			name := l.fullTag(field, tag)

aconfigdotenv/dotenv.go

@@ -10,6 +10,11 @@ type Decoder struct{}
 // New .ENV decoder for aconfig.
 func New() *Decoder { return &Decoder{} }
 
+// Format of the decoder.
+func (d *Decoder) Format() string {
+	return "env"
+}
+
 // DecodeFile implements aconfig.FileDecoder.
 func (d *Decoder) DecodeFile(filename string) (map[string]interface{}, error) {
 	raw, err := godotenv.Read(filename)

aconfighcl/hcl.go

@@ -12,6 +12,11 @@ type Decoder struct{}
 // New HCL decoder for aconfig.
 func New() *Decoder { return &Decoder{} }
 
+// Format of the decoder.
+func (d *Decoder) Format() string {
+	return "hcl"
+}
+
 // DecodeFile implements aconfig.FileDecoder.
 func (d *Decoder) DecodeFile(filename string) (map[string]interface{}, error) {
 	b, err := ioutil.ReadFile(filename)

aconfigtoml/toml.go

@@ -12,6 +12,11 @@ type Decoder struct{}
 // New TOML decoder for aconfig.
 func New() *Decoder { return &Decoder{} }
 
+// Format of the decoder.
+func (d *Decoder) Format() string {
+	return "toml"
+}
+
 // DecodeFile implements aconfig.FileDecoder.
 func (d *Decoder) DecodeFile(filename string) (map[string]interface{}, error) {
 	f, err := os.Open(filename)

aconfigyaml/yaml.go

@@ -12,6 +12,11 @@ type Decoder struct{}
 // New YAML decoder for aconfig.
 func New() *Decoder { return &Decoder{} }
 
+// Format of the decoder.
+func (d *Decoder) Format() string {
+	return "yaml"
+}
+
 // DecodeFile implements aconfig.FileDecoder.
 func (d *Decoder) DecodeFile(filename string) (map[string]interface{}, error) {
 	f, err := os.Open(filename)

utils.go

@@ -23,14 +23,6 @@ func assertStruct(x interface{}) {
 	}
 }
 
-func getTagForExt(ext string) string {
-	tag := ext[1:]
-	if tag == "yml" {
-		tag = "yaml"
-	}
-	return tag
-}
-
 func getEnv() map[string]interface{} {
 	env := os.Environ()
 	res := make(map[string]interface{}, len(env))
@@ -137,6 +129,11 @@ func splitNameByWords(src string) []string {
 
 type jsonDecoder struct{}
 
+// Format of the decoder.
+func (d *jsonDecoder) Format() string {
+	return "json"
+}
+
 // DecodeFile implements FileDecoder.
 func (d *jsonDecoder) DecodeFile(filename string) (map[string]interface{}, error) {
 	f, err := os.Open(filename)