GNU bug report logs - #3647
23.1.50; defun* generates incorrect code for handling arglist keyword lookup

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Message #5 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Miles Bader <miles.bader <at> necel.com>
To: emacs-pretest-bug <at> gnu.org
Subject: 23.1.50; defun* generates incorrect code for handling arglist keyword lookup
Date: Mon, 22 Jun 2009 15:45:29 +0900

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:


Given the following code:

   (require 'cl)
   (defun* oink (&key a b) (list a b))

then evaluating:

   (oink :b :a :a 42)
   => (:a :a)

... which is incorrect.  The correct answer is (42 :A).

Looking at the macro-expansion of the above defun* form, the reason is
obvious:  the generated code uses (car (cdr (memq KEYWORD ARGLIST))) to
look up keyword argument values, which is obviously bogus if a preceding
argument value is the same as a keyword.  It would be more correct to
use (plist-get ARGUMENT KEYWORD), and that's what common-lisp systems I
tested return for this test.

However, the code in cl.el that generates keyword handling code is so
confusing, I'm not really sure how to fix this; presumably something in
`cl-do-arglist'?

Thanks,

-Miles


If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
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If you would like to further debug the crash, please read the file
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In GNU Emacs 23.1.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.16.2)
 of 2009-06-22 on dhlpc061
Windowing system distributor `The X.Org Foundation', version 11.0.10601901
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Message #10 received at 3647 <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: Miles Bader <miles <at> gnu.org>
Cc: 3647 <at> debbugs.gnu.org
Subject: Re: 23.1.50;
	defun* generates incorrect code for handling arglist keyword lookup
Date: Sat, 17 Sep 2011 08:19:24 +0200

Miles Bader <miles.bader <at> necel.com> writes:

> Please describe exactly what actions triggered the bug
> and the precise symptoms of the bug:
>
> Given the following code:
>
>    (require 'cl)
>    (defun* oink (&key a b) (list a b))
>
> then evaluating:
>
>    (oink :b :a :a 42)
>    => (:a :a)
>
> ... which is incorrect.  The correct answer is (42 :A).

I can confirm that this bug is still present in Emacs 24.

> Looking at the macro-expansion of the above defun* form, the reason is
> obvious:  the generated code uses (car (cdr (memq KEYWORD ARGLIST))) to
> look up keyword argument values, which is obviously bogus if a preceding
> argument value is the same as a keyword.  It would be more correct to
> use (plist-get ARGUMENT KEYWORD), and that's what common-lisp systems I
> tested return for this test.
>
> However, the code in cl.el that generates keyword handling code is so
> confusing, I'm not really sure how to fix this; presumably something in
> `cl-do-arglist'?

Hm.  I think that function could do with some well-placed comments.  :-)

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/

Message #15 received at 3647-done <at> debbugs.gnu.org (full text, mbox):

From: Daniel Colascione <dancol <at> dancol.org>
To: 3647-done <at> debbugs.gnu.org
Subject: Done
Date: Sat, 22 Mar 2014 23:20:41 -0700

[Message part 1 (text/plain, inline)]

Done

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