Update default tag key with custom tag key handling

masq.go

@@ -8,6 +8,10 @@ import (
 )
 
 const (
+	// DefaultTagKey is a default key name of struct tag for masq. WithCustomTagKey option can change this value.
+	DefaultTagKey = "masq"
+
+	// DefaultRedactMessage is a default message to replace redacted value. WithRedactMessage option can change this value.
 	DefaultRedactMessage = "[REDACTED]"
 )
 
@@ -31,7 +35,7 @@ func newMasq(options ...Option) *masq {
 	m := &masq{
 		redactMessage: DefaultRedactMessage,
 		allowedTypes:  map[reflect.Type]struct{}{},
-		tagKey:        "masq",
+		tagKey:        DefaultTagKey,
 	}
 	m.defaultRedactor = func(src, dst reflect.Value) bool {
 		switch src.Kind() {

options.go

@@ -35,8 +35,12 @@ func WithTag(tag string, redactors ...Redactor) Option {
 	return WithCensor(newTagCensor(tag), redactors...)
 }
 
-// WithCustomTagKey is an option to set the custom tag key. The default tag key is `masq`.
+// WithCustomTagKey is an option to set the custom tag key. The default tag key is `masq`. If the field has the target tag in the custom tag key AND the field is matched with the target tag specified by WithTag, the field will be redacted. If tagKey is empty, WithCustomTagKey panics.
 func WithCustomTagKey(tagKey string) Option {
+	if tagKey == "" {
+		panic("masq: tag key must not be empty")
+	}
+
 	return func(m *masq) {
 		m.tagKey = tagKey
 	}

options_test.go

@@ -149,6 +149,16 @@ func ExampleWithCustomTagKey() {
 	// {"level":"INFO","msg":"Got record","record":{"EMail":"[REDACTED]","ID":"m-mizutani"},"time":"2022-12-25T09:00:00.123456789"}
 }
 
+func TestCustomTagKeyPanic(t *testing.T) {
+	defer func() {
+		if recover() == nil {
+			t.Errorf("Failed to panic")
+		}
+	}()
+
+	masq.New(masq.WithCustomTagKey(""))
+}
+
 func ExampleWithFieldName() {
 	out := &fixedTimeWriter{}