v2: Consider erroring or warning when trying to print on the scrollback buffer while AltScreen is enabled

[andreynering]

Take this snippet as an example:

package main

import (
	tea "github.com/charmbracelet/bubbletea/v2"
)

type model struct{}

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

func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	switch msg := msg.(type) {
	case tea.KeyMsg:
		switch msg.String() {
		case "q":
			return m, tea.Quit
		default:
			return m, tea.Printf("Key pressed: %s", msg.String())
		}
	}
	return m, nil
}

func (m model) View() string {
	return `Logging stuff. Press "q" to exit.`
}

func main() {
	p := tea.NewProgram(model{}, tea.WithAltScreen())
	if _, err := p.Run(); err != nil {
		panic(err)
	}
}

Because we're using tea.WithAltScreen(), the tea.Printf instructions are no-op and are not been print at all. Because these are used for debugging, the user may believe that some other feature is not working while it's actually just the debugging logs not being print due to AltScreen.

Before releasing v2 for real, we may consider adding some errors or warning somehow if tea.Printf is used together with tea.WithAltScreen(). Even a panic can be considered, but perhaps that's a bit too drastic?

Below, I'll paste the code paths until a return is reached, preventing the print:

bubbletea/tea.go

Lines 739 to 740 in 7858a14

	case printLineMessage:
	p.renderer.insertAbove(msg.messageBody)

bubbletea/cursed_renderer.go

Line 219 in 7858a14

s.scr.InsertAbove(lines)

https://github.com/charmbracelet/x/blob/92fd130481998d7760473ae5b14c1a9bc90b9df3/cellbuf/screen.go#L1449-L1451

/cc @aymanbagabas

[aymanbagabas]

This is intentional, Printf was never meant to be for debugging. The purpose was always to insert lines above the program managed screen. When using the alt-screen, the whole terminal screen is used and inserting lines above it just means pushing them to the scroll buffer (if any).

Instead, maybe we can come up with other names that clearly signify the behavior of Printf/Println.