feat: add support to nested structs

flags.go

@@ -65,6 +65,8 @@ func (f Flags) SetDefault(long string, val any) bool {
 	return false
 }
 
+// BuildFlags creates a slice of Flags from a struct.
+// It supports nested structs and will only generate flags if it finds a 'short' and 'long' tag.
 func BuildFlags(obj any) Flags {
 	v := reflect.ValueOf(obj)
 	if v.Kind() != reflect.Ptr {
@@ -74,19 +76,39 @@ func BuildFlags(obj any) Flags {
 	if v.Kind() != reflect.Struct {
 		panic(fmt.Errorf("expected a struct, got %s", v.Kind()))
 	}
+
+	return buildFlagsRecursive(v)
+}
+
+func buildFlagsRecursive(v reflect.Value) Flags {
 	t := v.Type()
+	var flags Flags
 
-	var err error
-	flags := make([]Flag, t.NumField())
 	for i := 0; i < t.NumField(); i++ {
-		flags[i], err = buildFlag(v.Field(i), t.Field(i))
-		if err != nil {
-			panic(err)
+		field := t.Field(i)
+		fieldValue := v.Field(i)
+
+		// Only process fields with a 'short' or 'long' tag
+		if hasTag(field.Tag, "short"); hasTag(field.Tag, "long") {
+			flag, err := buildFlag(fieldValue, field)
+			if err != nil {
+				panic(err)
+			}
+			flags = append(flags, flag)
+		} else if fieldValue.Kind() == reflect.Struct {
+			// If the field is a struct, recurse into it
+			embeddedFlags := buildFlagsRecursive(fieldValue)
+			flags = append(flags, embeddedFlags...)
 		}
 	}
 	return flags
 }
 
+func hasTag(tag reflect.StructTag, key string) bool {
+	_, ok := tag.Lookup(key)
+	return ok
+}
+
 func buildFlag(val reflect.Value, sf reflect.StructField) (Flag, error) {
 	const (
 		tagNameLong       = "long"