EnterAlternateScreen does not overwrite what is already on TTY/VT

[eatradish]

Describe the bug
EnterAlternateScreen does not overwrite what is already on TTY/VT

To Reproduce

1. Run echo "hi" on Linux tty
2. Run this program:

use std::{
    io::{self, stdout},
    time::Duration,
};

use crossterm::{
    cursor::position,
    event::{poll, read, Event, KeyCode},
    execute,
    terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen},
};

fn main() {
    enable_raw_mode().unwrap();
    execute!(stdout(), EnterAlternateScreen).unwrap();

    if let Err(e) = print_events() {
        println!("Error: {:?}\r", e);
    }

    disable_raw_mode().unwrap();
}

fn print_events() -> io::Result<()> {
    loop {
        // Wait up to 1s for another event
        if poll(Duration::from_millis(1_000))? {
            // It's guaranteed that read() won't block if `poll` returns `Ok(true)`
            let event = read()?;

            println!("Event::{:?}\r", event);

            if event == Event::Key(KeyCode::Char('c').into()) {
                println!("Cursor position: {:?}\r", position());
            }

            if event == Event::Key(KeyCode::Esc.into()) {
                break;
            }
        } else {
            // Timeout expired, no event for 1s
            println!(".\r");
        }
    }

    Ok(())
}

3. On tty, it seems that EnterAlternateScreen doesn't take effect (you can see the hi output directly), whereas on the terminal emulator it does.

Expected behavior
EnterAlternateScreen has the same behavior as other terminal emulators under tty

OS
Linux

Terminal/Console

• tty

[joshka]

Try running tput smcup to switch to the alt screen and tput rmcup to restore. If this does nothing, then your tty doesn't support the alternate screen (or it's disabled by config), and there's likely nothing we can do here. If it does then your tty likely has some alternative escape code to make this change. You'll need to dig into the termcap / terminfo to work out what's going on.