[debbugs-tracker] bug#19734: closed (25.0.50; nested backquotes: recent changes not backward compatible)

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Your message dated Fri, 30 Jan 2015 16:01:55 -0500
with message-id <address@hidden>
and subject line Re: bug#19734: 25.0.50; nested backquotes: recent changes not 
backward compatible
has caused the debbugs.gnu.org bug report #19734,
regarding 25.0.50; nested backquotes: recent changes not backward compatible
to be marked as done.

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19734: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=19734
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> --- Begin Message ---
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> Subject: 
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> 25.0.50; nested backquotes: recent changes not backward compatible
>
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>
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> Date: 
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> Fri, 30 Jan 2015 18:49:52 +0100
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>
> Hello,
>
> Recent changes in backquote.el, I guess especially in this commit:
>
> 86009dd5d886f1101358990e4f8f69a5d1467eb8
> Author: Stefan Monnier <address@hidden>
> Date:   Sat Nov 15 23:59:50 2014 -0500
>
>     * lisp/emacs-lisp/backquote.el (backquote-process): Optimize away
>       the ,' case.
>
> were not backwards compatible.  If this was intended (?), it should be
> mentioned in the news I think.
>
> Here is an example.  In Emacs 24, I had something like this in my config
> (massively shortened):
>
>
> --8<---------------cut here---------------start------------->8---
> (defun my-make-feh-cmd ()
>   "Return a feh command line suitble for dired.
> Take the current screen resolution at account."
>   (if (not window-system)
>       "feh"
>     (let* ((display-pixel-width (display-pixel-width))
>            (width (- display-pixel-width (frame-pixel-width))))
>       (format "feh -Z -g %sx%s+%s *"
>               width
>               (- (x-display-pixel-height) 30)
>               (min (+ (frame-pixel-width) 2) (- display-pixel-width width))))))
>
> (require 'dired-x)
>
> (let ((programs '("vlc *" "smplayer *")))
>   (setq-default
>    dired-guess-shell-alist-user
>    `((".*" (if (file-directory-p file)
>                `(,,'(my-make-feh-cmd) ;compute at runtime!
>                  ,@',programs)
>              ',programs)))))
> --8<---------------cut here---------------end--------------->8---
>
>
> In trunk, the backquote expression evals to something different now, and
> AFAICT
>
>     ,,'(my-make-feh-cmd)
>
> from above must now be
>
>       ,(my-make-feh-cmd)
>
> That looks less frightening, but I had to find this out myself because
> my code was broken and there was no news entry.
>
>
> Thanks,
>
> Michael.
>
>
>
>
> In GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.5)
>  of 2015-01-29 on drachen
> Repository revision: 1dc1959ebf50401c69adeb6d182950b59835f94d
> Windowing system distributor `The X.Org Foundation', version 11.0.11602901
> System Description:     Debian GNU/Linux 8.0 (jessie)
>
> Configured features:
> XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS NOTIFY
> LIBXML2 FREETYPE XFT ZLIB
>
>
>
>
> --- End Message ---
> --- Begin Message ---
>
>
>
> Subject: 
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> Re: bug#19734: 25.0.50; nested backquotes: recent changes not backward compatible
>
>
>
>
> Date: 
>
> Fri, 30 Jan 2015 16:01:55 -0500
>
>
>
>
> User-agent: 
>
> Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux)
>
>
>
>
> >     * lisp/emacs-lisp/backquote.el (backquote-process): Optimize away
> >       the ,' case.
> > were not backwards compatible.  If this was intended (?), it should be
> > mentioned in the news I think.
>
> As the commit message indicates, this was supposed to be an
> optimization, i.e. no change in observable behavior.
>
> > In trunk, the backquote expression evals to something different now, and
> >     ,,'(my-make-feh-cmd)
> > from above must now be
> >       ,(my-make-feh-cmd)
>
> Yes, your rewrite is correct and desirable, but indeed we had a bug
> which I've just fixed in master.  Thanks.
>
>
>         Stefan
>
>
> --- End Message ---