Maintain exec output

[raphaelvigee]

Ref #1275

[meowgorithm]

Hey, Raphaël! Thanks for the PR. Do you have any sample code to help illustrate the issue? Providing it will help us expedite this one.

We're using exec to print above inline TUIs quite a lot but haven't encountered this issue, so any sample code would really help illustrate the problem.

[raphaelvigee]

package main

import (
	"fmt"
	tea "github.com/charmbracelet/bubbletea"
	"io"
	"os"
	"strings"
)

type execCmd struct {
	w io.Writer
}

type execDoneMsg struct{}

func (e *execCmd) Run() error {
	for i := range 8 {
		e.w.Write([]byte(fmt.Sprintf("exec %v\n", i)))
	}

	return nil
}

func (e *execCmd) SetStdin(r io.Reader) {
}

func (e *execCmd) SetStdout(w io.Writer) {
	e.w = w
}

func (e *execCmd) SetStderr(w io.Writer) {
}

type model struct{}

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

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

	switch msg := msg.(type) {
	case tea.KeyMsg:
		switch msg.String() {
		case "ctrl+c", "q":
			return m, tea.Quit
		}
	case execDoneMsg:
		cmds = append(cmds, tea.Quit)
	}

	cmds = append(cmds, cmd)

	return m, tea.Batch(cmds...)
}

func (m model) View() string {
	var sb strings.Builder

	for i := range 5 {
		sb.WriteString(fmt.Sprintf("view %v\n", i))
	}

	return sb.String()
}

func main() {
	initialModel := model{}

	p := tea.NewProgram(initialModel)

	go func() {
		p.Send(
			tea.Exec(&execCmd{}, func(err error) tea.Msg {
				return execDoneMsg{}
			})(),
		)
	}()

	if _, err := p.Run(); err != nil {
		fmt.Println("Error:", err)
		os.Exit(1)
	}
}

Current:

view 0
view 1
view 2
view 3
view 4
exec 0
exec 1
exec 2
view 0
view 1
view 2
view 3
view 4

i only see 3 lines from exec, but i expect to see all 8 lines that were printed

With fix:

view 0
view 1
view 2
view 3
view 4
exec 0
exec 1
exec 2
exec 3
exec 4
exec 5
exec 6
exec 7
view 0
view 1
view 2
view 3
view 4