Исправлено повторное определение флага.

cli.go

@@ -313,6 +313,7 @@ func (c *Command) addFlag(value reflect.Value, field reflect.StructField) error
 			return ErrInternalError
 		},
 		)
+		return nil
 	}
 
 	kind := value.Kind()

cli_test.go

@@ -17,6 +17,7 @@ package config
 
 import (
 	"flag"
+	"log/slog"
 	"os"
 	"strconv"
 	"testing"
@@ -299,3 +300,20 @@ func TestDurationWithEqual(t *testing.T) {
 	assert.NoError(cmd.Parse(cmd.Args))
 	assert.Equal(time.Second*5, conf.interval)
 }
+
+func TestLogLevel(t *testing.T) {
+	assert := assert.New(t)
+	var conf struct {
+		Level slog.Level `cli:"log-level" default:"INFO"`
+	}
+
+	cmd := NewCLI("Config")
+	assert.NoError(cmd.Init(&conf), "init config command")
+
+	args := []string{"-v", "-log-level", "DEBUG", "help"}
+
+	assert.ElementsMatch([]string{"-v", "help"}, cmd.Capture(args))
+	assert.ElementsMatch([]string{"-log-level", "DEBUG"}, cmd.Args)
+	assert.NoError(cmd.Parse(cmd.Args))
+	assert.Equal(slog.LevelDebug, conf.Level)
+}