Add support for field name remapping hook

mapstructure.go

@@ -91,6 +91,12 @@ type DecoderConfig struct {
 	// The tag name that mapstructure reads for field names. This
 	// defaults to "mapstructure"
 	TagName string
+
+	// Extra transformation methods to match field name from map to struct.
+	// Options:
+	// - snake (snake_case: all characters in lower case and concatenating words by '_')
+	// - kebab (kebab-case: all characters in lower case and concatenating words by '-' )
+	FieldNameTransFormMethod string
 }
 
 // A Decoder takes a raw interface value and turns it into structured
@@ -1064,7 +1070,16 @@ func (d *Decoder) decodeStructFromMap(name string, dataVal, val reflect.Value) e
 					continue
 				}
 
-				if strings.EqualFold(mK, fieldName) {
+				matched := strings.EqualFold(mK, fieldName)
+
+				switch d.config.FieldNameTransFormMethod {
+				case "snake":
+					matched = matched || strings.EqualFold(strings.ReplaceAll(mK, "_", ""), fieldName)
+				case "kabab":
+					matched = matched || strings.EqualFold(strings.ReplaceAll(mK, "-", ""), fieldName)
+				}
+
+				if matched {
 					rawMapKey = dataValKey
 					rawMapVal = dataVal.MapIndex(dataValKey)
 					break

mapstructure_test.go

@@ -906,6 +906,34 @@ func TestDecoder_ErrorUnused(t *testing.T) {
 	}
 }
 
+func TestDecode_FieldNameTransForm(t *testing.T) {
+	t.Parallel()
+
+	input := map[string]interface{}{
+		"v_string": "WHAT",
+	}
+
+	var result Basic
+	config := &DecoderConfig{
+		Result:                   &result,
+		FieldNameTransFormMethod: "snake",
+	}
+
+	decoder, err := NewDecoder(config)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	err = decoder.Decode(input)
+	if err != nil {
+		t.Fatalf("got an err: %s", err)
+	}
+
+	if result.Vstring != "WHAT" {
+		t.Errorf("vstring should be WHAT: %#v", result.Vstring)
+	}
+}
+
 func TestMap(t *testing.T) {
 	t.Parallel()