Move implementation of +hold to Go

No need to pay python interpreter startup cost for --hold

tools/tui/hold.go

@@ -0,0 +1,72 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package tui
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+
+	"kitty/tools/tui/loop"
+)
+
+var _ = fmt.Print
+
+func HoldTillEnter(start_with_newline bool) {
+	lp, err := loop.New(loop.NoAlternateScreen, loop.NoRestoreColors, loop.NoMouseTracking)
+	if err != nil {
+		return
+	}
+	lp.OnInitialize = func() (string, error) {
+		lp.SetCursorVisible(false)
+		if start_with_newline {
+			lp.QueueWriteString("\r\n")
+		}
+		lp.QueueWriteString("\x1b[1;32mPress Enter or Esc to exit\x1b[m")
+		return "", nil
+	}
+	lp.OnFinalize = func() string {
+		lp.SetCursorVisible(true)
+		return ""
+	}
+
+	lp.OnKeyEvent = func(event *loop.KeyEvent) error {
+		if event.MatchesPressOrRepeat("enter") || event.MatchesPressOrRepeat("esc") || event.MatchesPressOrRepeat("ctrl+c") || event.MatchesPressOrRepeat("ctrl+d") {
+			event.Handled = true
+			lp.Quit(0)
+		}
+		return nil
+	}
+	lp.Run()
+}
+
+func ExecAndHoldTillEnter(cmdline []string) {
+	if len(cmdline) == 0 {
+		HoldTillEnter(false)
+		os.Exit(0)
+	}
+	var cmd *exec.Cmd
+	if len(cmdline) == 1 {
+		cmd = exec.Command(cmdline[0])
+	} else {
+		cmd = exec.Command(cmdline[0], cmdline[1:]...)
+	}
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	var ee *exec.ExitError
+	err := cmd.Run()
+	is_exit_error := err != nil && errors.As(err, &ee)
+	if err != nil && !is_exit_error {
+		fmt.Fprintln(os.Stderr, err)
+	}
+	HoldTillEnter(true)
+	if err == nil {
+		os.Exit(0)
+	}
+	if is_exit_error {
+		os.Exit(ee.ExitCode())
+	}
+	os.Exit(1)
+}

tools/tui/loop/api.go

@@ -242,6 +242,14 @@ func (self *Loop) SetCursorShape(shape CursorShapes, blink bool) {
 	self.QueueWriteString(CursorShape(shape, blink))
 }
 
+func (self *Loop) SetCursorVisible(visible bool) {
+	if visible {
+		self.QueueWriteString(DECTCEM.EscapeCodeToSet())
+	} else {
+		self.QueueWriteString(DECTCEM.EscapeCodeToReset())
+	}
+}
+
 func (self *Loop) MoveCursorHorizontally(amt int) {
 	if amt != 0 {
 		suffix := "C"