)

var userTypeCache sync.Map // map[reflect.Type]*userTypeInfo

// validUserType returns, and saves, the information associated with user-provided type rt.
// If the user type is not valid, err will be non-nil. To be used when the error handler
// is not set up.
func validUserType(rt reflect.Type) (*userTypeInfo, error) {
	if ui, ok := userTypeCache.Load(rt); ok {
		return ui.(*userTypeInfo), nil
	}

	// goroutines can share an encoder.
	enc.mutex.Lock()
	defer enc.mutex.Unlock()

	// Remove any nested writers remaining due to previous errors.
	enc.w = enc.w[0:1]

	ut, err := validUserType(value.Type())
	if err != nil {
		return err
	}

	enc.err = nil
	enc.byteBuf.Reset()
	enc.byteBuf.Write(spaceForLength)
	state := enc.newEncoderState(&enc.byteBuf)