ValidateFunc Blocking Workaround

main.go

package main

import (
	"fmt"
	"log"

	"github.com/charmbracelet/bubbles/key"
	"github.com/charmbracelet/bubbles/textinput"
	tea "github.com/charmbracelet/bubbletea"
	"github.com/charmbracelet/lipgloss"
)

const maxWidth = 20

type errMsg error

var quitKeys = key.NewBinding(
	key.WithKeys("q", "esc", "ctrl+c"),
	key.WithHelp("", "press q to quit"),
)

var errStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("24")).Render

type model struct {
	input textinput.Model
	err   errMsg
}

/*
using textinput.Validate; causes blocking behaviour for invalid strings

	func checkLength() textinput.ValidateFunc {
		return func(s string) error {
			if len(s) > 0 {
				letter := rune(s[0])
				if !unicode.IsLetter(letter) {
					return errors.New("not valid input")
				}
			}
			return nil
		}
	}
*/

func checkLength(s string) error {
	if len(s) > 10 {
		return fmt.Errorf("length should be less than 10. current: %d", len(s))
	}
	return nil
}

func New() model {
	input := textinput.New()
	input.Focus()
	input.Width = 50
	return model{input, nil}
}

func (m model) Init() tea.Cmd {
	return textinput.Blink
}

func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	var cmd tea.Cmd

	switch msg := msg.(type) {
	case tea.KeyMsg:
		if key.Matches(msg, quitKeys) {
			return m, tea.Quit
		}
	case errMsg:
		m.err = msg
		return m, nil

	}
	m.input, cmd = m.input.Update(msg)
	// if we were using textinput validate:
	// m.err = m.input.Validate(m.input.Value())
	m.err = checkLength(m.input.Value())
	return m, cmd
}

func (m model) View() string {
	if m.err != nil {
		return lipgloss.JoinVertical(lipgloss.Left, m.input.View(), errStyle(m.err.Error()))
	}
	return m.input.View()
}

func main() {
	p := tea.NewProgram(New())
	if _, err := p.Run(); err != nil {
		log.Fatal(err)
	}
}