Add convenience function MustLocalizeMessage (#352)

Added a must variant of `LocalizeMessage` (like `Localize` &
`MustLocalize`)

i18n/localizer.go

@@ -124,7 +124,7 @@ func (l *Localizer) Localize(lc *LocalizeConfig) (string, error) {
 	return msg, err
 }
 
-// Localize returns a localized message.
+// LocalizeMessage returns a localized message.
 func (l *Localizer) LocalizeMessage(msg *Message) (string, error) {
 	return l.Localize(&LocalizeConfig{
 		DefaultMessage: msg,
@@ -236,3 +236,12 @@ func (l *Localizer) MustLocalize(lc *LocalizeConfig) string {
 	}
 	return localized
 }
+
+// MustLocalizeMessage is similar to LocalizeMessage, except it panics if an error happens.
+func (l *Localizer) MustLocalizeMessage(msg *Message) string {
+	localized, err := l.LocalizeMessage(msg)
+	if err != nil {
+		panic(err)
+	}
+	return localized
+}

i18n/localizer_test.go

@@ -768,3 +768,14 @@ func TestMustLocalize(t *testing.T) {
 		MessageID: "hello",
 	})
 }
+
+func TestMustLocalizeMessage(t *testing.T) {
+	defer func() {
+		if recover() == nil {
+			t.Fatalf("MustLocalizeMessage did not panic")
+		}
+	}()
+	bundle := NewBundle(language.English)
+	localizer := NewLocalizer(bundle)
+	localizer.MustLocalizeMessage(&Message{})
+}