use index tag first, field name second (#168)

moov-io · Mar 1, 2022 · d04444b · d04444b
1 parent 43d0fdb
commit d04444b
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Showing 4 changed files with 29 additions and 7 deletions.
diff --git a/field/composite.go b/field/composite.go
@@ -476,13 +476,13 @@ var fieldNameTagRe = regexp.MustCompile(`^F.+$`)
 func getFieldIndexOrTag(field reflect.StructField) (string, error) {
 	dataFieldName := field.Name
 
-	if len(dataFieldName) > 0 && fieldNameTagRe.MatchString(dataFieldName) {
-		return dataFieldName[1:], nil
-	}
-
 	if fieldIndex := field.Tag.Get("index"); fieldIndex != "" {
 		return fieldIndex, nil
 	}
 
+	if len(dataFieldName) > 0 && fieldNameTagRe.MatchString(dataFieldName) {
+		return dataFieldName[1:], nil
+	}
+
 	return "", nil
 }
diff --git a/field/composite_test.go b/field/composite_test.go
@@ -1051,6 +1051,17 @@ func TestComposite_getFieldIndexOrTag(t *testing.T) {
 		require.Equal(t, "1", index)
 	})
 
+	t.Run("returns index from field tag instead of field name when both match", func(t *testing.T) {
+		st := reflect.ValueOf(&struct {
+			F1 string `index:"AB"`
+		}{}).Elem()
+
+		index, err := getFieldIndexOrTag(st.Type().Field(0))
+
+		require.NoError(t, err)
+		require.Equal(t, "AB", index)
+	})
+
 	t.Run("returns index from field tag", func(t *testing.T) {
 		st := reflect.ValueOf(&struct {
 			Name string `index:"abcd"`

diff --git a/message.go b/message.go
@@ -406,8 +406,7 @@ var fieldNameIndexRe = regexp.MustCompile(`^F\d+$`)
 func getFieldIndex(field reflect.StructField) (int, error) {
 	dataFieldName := field.Name
 
-	if len(dataFieldName) > 0 && fieldNameIndexRe.MatchString(dataFieldName) {
-		indexStr := dataFieldName[1:]
+	if indexStr := field.Tag.Get("index"); indexStr != "" {
 		fieldIndex, err := strconv.Atoi(indexStr)
 		if err != nil {
 			return -1, fmt.Errorf("converting field index into int: %w", err)
@@ -416,7 +415,8 @@ func getFieldIndex(field reflect.StructField) (int, error) {
 		return fieldIndex, nil
 	}
 
-	if indexStr := field.Tag.Get("index"); indexStr != "" {
+	if len(dataFieldName) > 0 && fieldNameIndexRe.MatchString(dataFieldName) {
+		indexStr := dataFieldName[1:]
 		fieldIndex, err := strconv.Atoi(indexStr)
 		if err != nil {
 			return -1, fmt.Errorf("converting field index into int: %w", err)

diff --git a/message_test.go b/message_test.go
@@ -1161,6 +1161,17 @@ func Test_getFieldIndex(t *testing.T) {
 		require.Equal(t, 1, index)
 	})
 
+	t.Run("returns index from field tag instead of field name when both match", func(t *testing.T) {
+		st := reflect.ValueOf(&struct {
+			F1 string `index:"2"`
+		}{}).Elem()
+
+		index, err := getFieldIndex(st.Type().Field(0))
+
+		require.NoError(t, err)
+		require.Equal(t, 2, index)
+	})
+
 	t.Run("returns index from field tag", func(t *testing.T) {
 		st := reflect.ValueOf(&struct {
 			Name   string `index:"abcd"`