Detect typed input without swallowing characters

[Marc Cornellà <hello@xxxxxxxxxxxxx>]

Hi,

in Oh My Zsh we want to detect whether the user has typed characters
before showing the prompt to auto-update, so that if they have, to
skip it entirely and get them to the prompt as fast as possible.

The current solution is to detect whether there's input with `read -t
-k 1`, but this solution has the downside of swallowing one character.

I've been looking at sysread and zselect to poll stdin (fd 0), but I
believe they only tell whether stdin is ready for reading, not whether
it holds any data. These are the commands I'm using by the way:

    sysread -t 0 -i 0
    zselect -t 0 -r 0

Is there any way to do this or should I give up entirely?

Thanks!
Marc