feat(encoding)!: accept a map in the decoder interface

This interface is specific to decoding data into Viper's internal,
so it's okay to make it Viper specific.

BREAKING CHANGE: the decoder interface now accepts a map instead of an
interface
Signed-off-by: Mark Sagi-Kazar <mark.sagikazar@gmail.com>

internal/encoding/decoder.go

@@ -4,10 +4,10 @@ import (
 	"sync"
 )
 
-// Decoder decodes the contents of b into a v representation.
+// Decoder decodes the contents of b into v.
 // It's primarily used for decoding contents of a file into a map[string]interface{}.
 type Decoder interface {
-	Decode(b []byte, v interface{}) error
+	Decode(b []byte, v map[string]interface{}) error
 }
 
 const (
@@ -48,7 +48,7 @@ func (e *DecoderRegistry) RegisterDecoder(format string, enc Decoder) error {
 }
 
 // Decode calls the underlying Decoder based on the format.
-func (e *DecoderRegistry) Decode(format string, b []byte, v interface{}) error {
+func (e *DecoderRegistry) Decode(format string, b []byte, v map[string]interface{}) error {
 	e.mu.RLock()
 	decoder, ok := e.decoders[format]
 	e.mu.RUnlock()

internal/encoding/decoder_test.go

 package encoding
 
 import (
+	"reflect"
 	"testing"
 )
 
 type decoder struct {
-	v interface{}
+	v map[string]interface{}
 }
 
-func (d decoder) Decode(_ []byte, v interface{}) error {
-	rv := v.(*string)
-	*rv = d.v.(string)
+func (d decoder) Decode(_ []byte, v map[string]interface{}) error {
+	for key, value := range d.v {
+		v[key] = value
+	}
 
 	return nil
 }
@@ -44,7 +46,9 @@ func TestDecoderRegistry_Decode(t *testing.T) {
 	t.Run("OK", func(t *testing.T) {
 		registry := NewDecoderRegistry()
 		decoder := decoder{
-			v: "decoded value",
+			v: map[string]interface{}{
+				"key": "value",
+			},
 		}
 
 		err := registry.RegisterDecoder("myformat", decoder)
@@ -52,24 +56,24 @@ func TestDecoderRegistry_Decode(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		var v string
+		v := map[string]interface{}{}
 
-		err = registry.Decode("myformat", []byte("some value"), &v)
+		err = registry.Decode("myformat", []byte("key: value"), v)
 		if err != nil {
 			t.Fatal(err)
 		}
 
-		if v != "decoded value" {
-			t.Fatalf("expected 'decoded value', got: %#v", v)
+		if !reflect.DeepEqual(decoder.v, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %+v\nexpected: %+v", v, decoder.v)
 		}
 	})
 
 	t.Run("DecoderNotFound", func(t *testing.T) {
 		registry := NewDecoderRegistry()
 
-		var v string
+		v := map[string]interface{}{}
 
-		err := registry.Decode("myformat", []byte("some value"), &v)
+		err := registry.Decode("myformat", nil, v)
 		if err != ErrDecoderNotFound {
 			t.Fatalf("expected ErrDecoderNotFound, got: %v", err)
 		}

internal/encoding/hcl/codec.go

@@ -35,6 +35,6 @@ func (Codec) Encode(v interface{}) ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
-func (Codec) Decode(b []byte, v interface{}) error {
-	return hcl.Unmarshal(b, v)
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	return hcl.Unmarshal(b, &v)
 }

internal/encoding/json/codec.go

@@ -12,6 +12,6 @@ func (Codec) Encode(v interface{}) ([]byte, error) {
 	return json.MarshalIndent(v, "", "  ")
 }
 
-func (Codec) Decode(b []byte, v interface{}) error {
-	return json.Unmarshal(b, v)
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	return json.Unmarshal(b, &v)
 }

internal/encoding/toml/codec.go

@@ -25,21 +25,16 @@ func (Codec) Encode(v interface{}) ([]byte, error) {
 	return toml.Marshal(v)
 }
 
-func (Codec) Decode(b []byte, v interface{}) error {
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
 	tree, err := toml.LoadBytes(b)
 	if err != nil {
 		return err
 	}
 
-	if m, ok := v.(*map[string]interface{}); ok {
-		vmap := *m
-		tmap := tree.ToMap()
-		for k, v := range tmap {
-			vmap[k] = v
-		}
-
-		return nil
+	tmap := tree.ToMap()
+	for key, value := range tmap {
+		v[key] = value
 	}
 
-	return tree.Unmarshal(v)
+	return nil
 }

internal/encoding/yaml/codec.go

@@ -9,6 +9,6 @@ func (Codec) Encode(v interface{}) ([]byte, error) {
 	return yaml.Marshal(v)
 }
 
-func (Codec) Decode(b []byte, v interface{}) error {
-	return yaml.Unmarshal(b, v)
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	return yaml.Unmarshal(b, &v)
 }

viper.go

@@ -1635,7 +1635,7 @@ func (v *Viper) unmarshalReader(in io.Reader, c map[string]interface{}) error {
 
 	switch format := strings.ToLower(v.getConfigType()); format {
 	case "yaml", "yml", "json", "toml", "hcl", "tfvars":
-		err := decoderRegistry.Decode(format, buf.Bytes(), &c)
+		err := decoderRegistry.Decode(format, buf.Bytes(), c)
 		if err != nil {
 			return ConfigParseError{err}
 		}