From 443f840a3b6bd0b8fc8d27fa20f3d5747a6a9d56 Mon Sep 17 00:00:00 2001
From: DarkiT <i@shabi.in>
Date: Tue, 21 Jan 2025 22:07:48 +0800
Subject: [PATCH] feat(decoder): support multiple tag names in order

Add support for comma-separated tag names in DecoderConfig.TagName.
The decoder will try each tag name in order and use the first valid tag value found.

Example:
  config := &DecoderConfig{
    TagName: "mapstructure,yaml,json",
    Result: &Config{},
  }

This allows more flexible struct field mapping by supporting multiple tag formats
while maintaining backwards compatibility with single tag name usage.

The decoder will:
1. Try each tag name in the specified order
2. Use the first valid tag value found
3. Fall back to field name if no tag found
4. Skip field if IgnoreUntaggedFields is true and no tag found

Changes:
- Update DecoderConfig.TagName comment to document multiple tag support
- Modify decodeStructFromMap to handle comma-separated tag names
- Keep backwards compatibility with single tag name usage
---
 mapstructure.go | 39 +++++++++++++++++++++++++++++----------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/mapstructure.go b/mapstructure.go
index e77e63b..a8aaa13 100644
--- a/mapstructure.go
+++ b/mapstructure.go
@@ -262,8 +262,8 @@ type DecoderConfig struct {
 	// value.
 	Result interface{}
 
-	// The tag name that mapstructure reads for field names. This
-	// defaults to "mapstructure"
+	// The tag names that mapstructure reads for field names, separated by comma.
+	// First found tag will be used. This defaults to "mapstructure"
 	TagName string
 
 	// The option of the value in the tag that indicates a field should
@@ -1007,7 +1007,7 @@ func (d *Decoder) decodeMapFromStruct(name string, dataVal reflect.Value, val re
 				continue
 			}
 			// If "omitempty" is specified in the tag, it ignores empty values.
-			if strings.Index(tagValue[index+1:], "omitempty") != -1 && isEmptyValue(v) {
+			if strings.Contains(tagValue[index+1:], "omitempty") && isEmptyValue(v) {
 				continue
 			}
 
@@ -1024,7 +1024,7 @@ func (d *Decoder) decodeMapFromStruct(name string, dataVal reflect.Value, val re
 					return fmt.Errorf("cannot squash non-struct type '%s'", v.Type())
 				}
 			} else {
-				if strings.Index(tagValue[index+1:], "remain") != -1 {
+				if strings.Contains(tagValue[index+1:], "remain") {
 					if v.Kind() != reflect.Map {
 						return fmt.Errorf("error remain-tag field with invalid type: '%s'", v.Type())
 					}
@@ -1430,13 +1430,32 @@ func (d *Decoder) decodeStructFromMap(name string, dataVal, val reflect.Value) e
 		field, fieldValue := f.field, f.val
 		fieldName := field.Name
 
-		tagValue := field.Tag.Get(d.config.TagName)
-		if tagValue == "" && d.config.IgnoreUntaggedFields {
-			continue
+		// Try each tag name in order until we find a match
+		tagNames := strings.Split(d.config.TagName, ",")
+		foundTag := false
+		for _, tagName := range tagNames {
+			tagName = strings.TrimSpace(tagName)
+			if tagName == "" {
+				continue
+			}
+
+			tagValue := field.Tag.Get(tagName)
+			if tagValue == "" {
+				continue
+			}
+
+			// Found a tag value, use it
+			tagValue = strings.SplitN(tagValue, ",", 2)[0]
+			if tagValue != "" {
+				fieldName = tagValue
+				foundTag = true
+				break
+			}
 		}
-		tagValue = strings.SplitN(tagValue, ",", 2)[0]
-		if tagValue != "" {
-			fieldName = tagValue
+
+		// Skip if no tag found and ignoring untagged fields
+		if !foundTag && d.config.IgnoreUntaggedFields {
+			continue
 		}
 
 		rawMapKey := reflect.ValueOf(fieldName)