bug#55883: [PATCH] Update X Primary Selection with active regions

[Eli Zaretskii]

> From: Duncan Findlay <duncf@google.com>
> Date: Mon, 13 Jun 2022 23:36:13 -0700
> Cc: 55883@debbugs.gnu.org
> 
> > > --- a/lisp/frame.el
> > > +++ b/lisp/frame.el
> > > @@ -2164,6 +2164,8 @@ display-selections-p
> > >         (not (null dos-windows-version))))
> > >       ((memq frame-type '(x w32 ns pgtk))
> > >        t)
> > > +     ((terminal-parameter display 'display-selections-p)
> > > +      t)
> >
> > This should test xterm--set-selection parameter.
> 
> OK, so the goal is to check the xterm--set-selection terminal
> parameter and variable xterm-select-active-regions before selecting
> the active region in deactivate-mark in simple.el.
> 
> We could do this in display-selections-p, but given that these
> variables are not obviously related to display-selections-p, it seems
> to me we probably want to do this check in deactivate-mark instead.
> Does that seem reasonable to you?

I think I'd prefer to have it in display-selections-p, like your last
version did, just using xterm--set-selection terminal parameter, not
the new one you invented.

> > I think the code should instead check the value of
> > xterm-select-active-regions in keyboard.c, where it decides whether to
> > set PRIMARY.  (Let me know if you need guidance for how to reference a
> > Lisp variable from C.)
> 
> This seems to work -- is there a better way?
> 
> !NILP (SYMBOL_VAL (XSYMBOL (Qxterm_select_active_regions)))

This is not safe, IMO.  I think this is better:

  if ((!NILP (Fwindow_system (Qnil))
       || ((symval = find_symbol_value (Qxterm_select_active_regions),
            (!EQ (symval, Qunbound) && !NILP (symval)))
            && !NILP (Fterminal_parameter (Qnil, Qxterm__set_selection))))

> I've also addressed Po's comments about long conditionals.

Thanks, the patch LGTM, modulo the above 2 minor nits.