switch to our own fork of pty which lets us set our own stdout and stderr

vendor/github.com/jesseduffield/pty/pty_linux.go

@@ -0,0 +1,51 @@
+package pty
+
+import (
+	"os"
+	"strconv"
+	"syscall"
+	"unsafe"
+)
+
+func open() (pty, tty *os.File, err error) {
+	p, err := os.OpenFile("/dev/ptmx", os.O_RDWR, 0)
+	if err != nil {
+		return nil, nil, err
+	}
+	// In case of error after this point, make sure we close the ptmx fd.
+	defer func() {
+		if err != nil {
+			_ = p.Close() // Best effort.
+		}
+	}()
+
+	sname, err := ptsname(p)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if err := unlockpt(p); err != nil {
+		return nil, nil, err
+	}
+
+	t, err := os.OpenFile(sname, os.O_RDWR|syscall.O_NOCTTY, 0)
+	if err != nil {
+		return nil, nil, err
+	}
+	return p, t, nil
+}
+
+func ptsname(f *os.File) (string, error) {
+	var n _C_uint
+	err := ioctl(f.Fd(), syscall.TIOCGPTN, uintptr(unsafe.Pointer(&n)))
+	if err != nil {
+		return "", err
+	}
+	return "/dev/pts/" + strconv.Itoa(int(n)), nil
+}
+
+func unlockpt(f *os.File) error {
+	var u _C_int
+	// use TIOCSPTLCK with a zero valued arg to clear the slave pty lock
+	return ioctl(f.Fd(), syscall.TIOCSPTLCK, uintptr(unsafe.Pointer(&u)))
+}