Function can_set_perm_invent

src/options.c:5487–5527

test whether 'perm_invent' can be toggled On */

/* test whether 'perm_invent' can be toggled On */
staticfn boolean
can_set_perm_invent(void)
{
    /*
     * Assumption: only called when iflags.perm_invent is False
     * and is about to be changed to True.
     */
    uchar old_perminv_mode = iflags.perminv_mode;

    if (!(windowprocs.wincap & WC_PERM_INVENT)) {
#ifdef TTY_GRAPHICS
#ifdef TTY_PERM_INVENT
        /* check tty, not necessarily the active window port;
           windows early startup can still be set to safeprocs */
        if (!check_tty_wincap(WC_PERM_INVENT))
#endif
#endif
            return FALSE;
    }

    if (iflags.perminv_mode == InvOptNone)
        iflags.perminv_mode = InvOptOn;

#ifdef TTY_PERM_INVENT
    if ((WINDOWPORT(tty)
         ) && !go.opt_initial) {
        perm_invent_toggled(FALSE);
        /* perm_invent_toggled()
           -> sync_perminvent()
              -> tty_create_nhwindow(NHW_PERMINVENT)
           gives feedback for failure (terminal too small) */
        if (WIN_INVEN == WIN_ERR) {
            iflags.perminv_mode = old_perminv_mode;
            return FALSE;
        }
    }
#else
    nhUse(old_perminv_mode);
#endif
    return TRUE;
}


#ifdef TTY_PERM_INVENT