Add support for slog.Level fields

additional.go

@@ -0,0 +1,19 @@
+package flagsfiller
+
+import (
+	"log/slog"
+	"reflect"
+)
+
+func init() {
+	RegisterSimpleType(slogLevelConverter)
+}
+
+func slogLevelConverter(s string, _ reflect.StructTag) (slog.Level, error) {
+	var level slog.Level
+	err := level.UnmarshalText([]byte(s))
+	if err != nil {
+		return slog.LevelInfo, err
+	}
+	return level, nil
+}

addtional_test.go

@@ -2,6 +2,7 @@ package flagsfiller_test
 
 import (
 	"flag"
+	"log/slog"
 	"net"
 	"net/netip"
 	"testing"
@@ -117,3 +118,59 @@ func TestTextUnmarshalerType(t *testing.T) {
 
 	assert.Equal(t, netip.AddrFrom4([4]byte{1, 2, 3, 4}), config.Addr)
 }
+
+func TestSlogLevels(t *testing.T) {
+	tests := []struct {
+		name     string
+		value    string
+		expected slog.Level
+	}{
+		{
+			name:     "info",
+			value:    "info",
+			expected: slog.LevelInfo,
+		},
+		{
+			name:     "error",
+			value:    "error",
+			expected: slog.LevelError,
+		},
+		{
+			name: "numeric offset",
+			// Borrowed from https://pkg.go.dev/log/slog#Level.UnmarshalText
+			value:    "Error-8",
+			expected: slog.LevelInfo,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			var args struct {
+				Level slog.Level
+			}
+
+			var flagset flag.FlagSet
+			err := flagsfiller.New().Fill(&flagset, &args)
+			require.NoError(t, err)
+
+			err = flagset.Parse([]string{"--level", test.value})
+			require.NoError(t, err)
+
+			assert.Equal(t, test.expected, args.Level)
+		})
+	}
+}
+
+func TestSlogLevelWithDefault(t *testing.T) {
+	var args struct {
+		Level slog.Level `default:"info"`
+	}
+
+	var flagset flag.FlagSet
+	err := flagsfiller.New().Fill(&flagset, &args)
+	require.NoError(t, err)
+
+	err = flagset.Parse([]string{})
+	require.NoError(t, err)
+
+	assert.Equal(t, slog.LevelInfo, args.Level)
+}

docs.go

@@ -146,6 +146,7 @@ FlagSetFiller also supports following field types:
 - net.IPNet: format used by net.ParseCIDR()
 - net.HardwareAddr (MAC addr): format used by net.ParseMAC()
 - time.Time: format is the layout string used by time.Parse(), default layout is time.DateTime, could be overriden by field tag "layout"
+- slog.Level: parsed as specified by https://pkg.go.dev/log/slog#Level.UnmarshalText, such as "info"
 
 # Environment variable mapping
 

flagset.go

@@ -200,7 +200,7 @@ func (f *FlagSetFiller) processField(flagSet *flag.FlagSet, fieldRef interface{}
 	if isSupportedStruct(fieldRef) {
 		handler := extendedTypes[getTypeName(t)]
 		err = handler(tag, fieldRef, hasDefaultTag, tagDefault, flagSet, renamed, usage, aliases)
-
+		return err
 	}
 
 	switch {

general.go

@@ -11,7 +11,7 @@ import (
 	"strings"
 )
 
-// this is a list of addtional supported types(include struct), like time.Time, that walkFields() won't walk into,
+// this is a list of additional supported types(include struct), like time.Time, that walkFields() won't walk into,
 // the key is the is string returned by the getTypeName(<type>),
 // each supported type need to be added in this map in init()
 var extendedTypes = make(map[string]handlerFunc)