Demonstrating a rendering bug

terminal_indent_breakage.go

/* 
Bug screenshot: https://tmp.shazow.net/screenshots/screenshot_2019-04-26_dd60.png
Output paste:
$ go run *.go
echo: "test"
echo: "foo"
echo: "bar"
 echo: "😼"
echo: "why do emojis break the echo indent?"
    echo: ""
   echo: "😼😼😼"
echo: "even erasing them and then hitting enter still breaks the indent"
prompt: 
*/
package main

import (
	"bytes"
	"fmt"
	"io"
	"log"
	"os"
	"strings"

	"golang.org/x/crypto/ssh/terminal"
)

type rw struct {
	io.Reader
	io.Writer
}

func main() {
	oldState, err := terminal.MakeRaw(0)
	if err != nil {
		panic(err)
	}
	defer terminal.Restore(0, oldState)

	screen := &rw{os.Stdin, os.Stdout}
	t := terminal.NewTerminal(screen, "prompt: ")

	t.SetEnterClear(true)

	var out bytes.Buffer
	for {
		line, err := t.ReadLine()
		if err == io.EOF {
			return
		} else if err != nil {
			log.Fatal(err)
		}
		if strings.HasPrefix(line, "/quit") {
			fmt.Fprintf(t, "Bye!\n")
			return
		}
		fmt.Fprintf(t, "echo: %q\n", line)
		out.Reset()
	}
}