Re: Removing redisplay-dont-pause

[Eli Zaretskii <eliz@gnu.org>]

Ping!  Any opinions?  Or should we install Gerd's changes?

> Date: Sun, 17 Nov 2024 09:11:01 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: emacs-devel@gnu.org, monnier@iro.umontreal.ca
> 
> > From: Gerd Möllmann <gerd.moellmann@gmail.com>
> > Cc: Stefan Monnier <monnier@iro.umontreal.ca>
> > Date: Sun, 17 Nov 2024 06:43:06 +0100
> > 
> > Eli Zaretskii <eliz@gnu.org> writes:
> > 
> > >> branch: scratch/tty-child-frames
> > >> commit f62d70f52f4f6b7ed158d618bf790df21f171172
> > >> Author: Gerd Möllmann <gerd@gnu.org>
> > >> Commit: Gerd Möllmann <gerd@gnu.org>
> > >>
> > >>     Don't pause display for pending input
> > >>
> > >>     * src/dispnew.c: Remove display_completed, redisplay_dont_pause,
> > >>     redisplay-dont-pause was declared obsolete in Emacs 24.  Remove anything
> > >>     checking pending input, change function signatures accordingly, and so
> > >>     on.
> > >>
> > >>     * src/keyboard.c (read_char): Don't use redisplay_dont_pause.
> > >>     * src/minibuf.c (read_minibuf): Use new function signatures.
> > >>     * src/xdisp.c: Don't check display_completed. Use new API.
> > >>
> > >>     * lisp/subr.el (redisplay-dont-pause): Remove declaration.
> > >
> > > I don't think this kind of change is appropriate.  Feature branches
> > > should not add/remove features not directly related to the feature
> > > being developed on the branch.  If we want to remove
> > > redisplay-dont-pause from Emacs (and I'm not yet sure we do), it
> > > should be discussed on emacs-devel or in a dedicated bug report, not
> > > silently installed on the branch.
> > 
> > I guess not many know what this is about, so what is this about?
> > 
> > One feature of the old redisplay was that it stopped updating the
> > display when it detected that input was pending, so that it could
> > process that input ASAP.
> > 
> > I kept that feature in my redisplay. As a debugging aid, I added
> > redisplay-dont-pause with which I could turn this feature on and off,
> > because pausing the display lead to a lot subtle and difficult to debug
> > bugs.
> > 
> > ISTR that setting redisplay-dont-pause to t became sort of a secret
> > semi-popular hack. Hyrum's Law in action, I guess. And 13 years ago or
> > so, the default of redisplay-dont-pause was changed to t by Eli.
> > 
> > 10 years ago, Stefan Monnier explained the why
> > 
> >   +  /* Contrary to expectations, a value of "false" can be detrimental to
> >   +     responsiveness since aborting a redisplay throws away some of the
> >   +     work already performed.  It's usually more efficient (and gives
> >   +     more prompt feedback to the user) to let the redisplay terminate,
> >   +     and just completely skip the next command's redisplay (which is
> >   +     done regardless of this setting if there's pending input at the
> >   +     beginning of the next redisplay).  */
> >   +  redisplay_dont_pause = true;
> > 
> > And finally, Stefan also
> > 
> >   (make-obsolete-variable 'redisplay-dont-pause nil "24.5")
> > 
> > and removed it from the docs.
> > 
> > I've removed that pausing feature in my fork and thought I'd bring that
> > to master via scratch/tty-child-frames, but apparently that's
> > controversial for some reason I don't understand, and I reverted that.
> > And so, here we are.
> 
> Thanks for the summary.
> 
> So what do people think about removing this variable (and the code
> supporting it) from Emacs?  In particular, does anyone use that
> variable in a non-default nil value?
> 
>