bug#42837: closed (26.3; `cl-incf' returns wrong value for (alist-get 'X ALIST 0) when ALIST is nil)

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Your message dated Thu, 13 Aug 2020 08:55:25 -0700
with message-id 
<CADwFkmkjgsFJ4as+EhWwOCLt8CUwHhRTVif6kNxHDLQEyQ_sjg@mail.gmail.com>
and subject line Re: bug#42837: 26.3; `cl-incf' returns wrong value for 
(alist-get 'X ALIST 0) when ALIST is nil
has caused the debbugs.gnu.org bug report #42837,
regarding 26.3; `cl-incf' returns wrong value for (alist-get 'X ALIST 0) when 
ALIST is nil
to be marked as done.

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42837: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=42837
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> --- Begin Message ---
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>
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> Subject: 
>
> 26.3; `cl-incf' returns wrong value for (alist-get 'X ALIST 0) when ALIST is nil
>
>
>
>
> Date: 
>
> Wed, 12 Aug 2020 21:58:30 +0000 (UTC)
>
>
>
>
> `cl-incf' should always return the new value of PLACE, after it is
> incremented.  It doesn't, if PLACE is an `alist-get' that returns the
> default value.
>
> (setq ali ())
>
> (cl-incf (alist-get 'a ali 0))
>
> returns ((a . 1)), but it should return just 1, the incremented value 
> associated with key `a'.
>
> This is the definition of `cl-incf':
>
> (defmacro cl-incf (place &optional x)
>   "Increment PLACE by X (1 by default).
> PLACE may be a symbol, or any generalized variable allowed by `setf'.
> The return value is the incremented value of PLACE."
>   (declare (debug (place &optional form)))
>   (if (symbolp place)
>       (list 'setq place (if x (list '+ place x) (list '1+ place)))
>     (list 'cl-callf '+ place (or x 1))))
>
> The definition should be something like this (not generally tested;
> might need some fixes, more hygiene, or optimization):
>
> (defmacro cl-incf (place &optional x)
>   "Increment PLACE by X (1 by default).
> PLACE may be a symbol, or any generalized variable allowed by `setf'.
> The return value is the incremented value of PLACE."
>   (declare (debug (place &optional form)))
>   (if (symbolp place)
>       (list 'setq place (if x (list '+ place x) (list '1+ place)))
>     `(progn
>        (cl-callf + ,place (or ,x 1))
>        ,place)))
>
> IOW, after updating the alist entry, `cl-incf' needs to return the new
> value for the given key.  `cl-callf' currently returns the entire alist.
>
> See this question from user `grepcake', who uncovered the problem:
>
> https://emacs.stackexchange.com/q/60097/105
>
>
> In GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
>  of 2019-08-29
> Repository revision: 96dd0196c28bc36779584e47fffcca433c9309cd
> Windowing system distributor `Microsoft Corp.', version 10.0.18362
> Configured using:
>  `configure --without-dbus --host=x86_64-w64-mingw32
>  --without-compress-install 'CFLAGS=-O2 -static -g3''
>
>
>
> --- End Message ---
> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: bug#42837: 26.3; `cl-incf' returns wrong value for (alist-get 'X ALIST 0) when ALIST is nil
>
>
>
>
> Date: 
>
> Thu, 13 Aug 2020 08:55:25 -0700
>
>
>
>
> User-agent: 
>
> Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)
>
>
>
>
> Drew Adams <drew.adams@oracle.com> writes:
>
> > `cl-incf' should always return the new value of PLACE, after it is
> > incremented.  It doesn't, if PLACE is an `alist-get' that returns the
> > default value.
> >
> > (setq ali ())
> >
> > (cl-incf (alist-get 'a ali 0))
> >
> > returns ((a . 1)), but it should return just 1, the incremented value
> > associated with key `a'.
>
> I can reproduce this on Emacs 26.3 (under emacs -Q).  But it seems to
> have been fixed on emacs-27 and current master, where I get:
>
> (progn
>    (require 'cl-lib)
>    (setq ali ())
>    (cl-incf (alist-get 'a ali 0)))
>
> => 1
>
> I'm therefore closing this bug report.
>
> Best regards,
> Stefan Kangas
>
>
> --- End Message ---