Function parse_display_with_file_exists_callback 

pub fn parse_display_with_file_exists_callback(
    dpy_name: &str,
    file_exists: impl Fn(&str) -> bool,
) -> Result<ParsedDisplay, DisplayParsingError>

Parse an X11 display string.

If dpy_name is None, the display is parsed from the environment variable DISPLAY.

The parameter file_exists is called to check whether a given string refers to an existing file. This function does not need to check the file type.