Subject: bug#29799: closed (Re: bug#29799: 24.5; cl-loop guard clause missing)

From: [email-masked] (GNU bug Tracking System)
Date: Mon, 08 Jan 2018 10:21:02 +0000

Your bug report

#29799: 24.5; cl-loop guard clause missing

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to [email-masked].

-- 
29799: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=29799
GNU Bug Tracking System
Contact [email-masked] with problems

Subject: Re: bug#29799: 24.5; cl-loop guard clause missing
From: Tino Calancha <[email-masked]>
To: [email-masked]
Date: Mon, 08 Jan 2018 19:20:35 +0900
List-Id: <debbugs-submit.debbugs.gnu.org>

Noam Postavsky <[email-masked]> writes:

> Tino Calancha <[email-masked]> writes:
>
>>     Fix #Bug#29799
>>     
>>     * lisp/emacs-lisp/cl-macs.el (cl--loop-guard-cond): New variable.
>>     (cl--parse-loop-clause): Set it non-nil if the loop contains
>>     a for/as clause.
>>     (cl-loop): After update the loop variable, update other variables
>>     only if cl--loop-guard-cond is non-nil.
>>     
>>     * test/lisp/emacs-lisp/cl-macs-tests.el (cl-macs-loop-for-as-equals-and):
>>     New test.
>
> Looks good, but please add some more info to the summary line.
Thank you very much.
Extended the commit message with more detailed explanations.

Fixed in master branch as commit 'cl-loop: Add missing guard condition'
(a0365437c9ee308ad7978e436631020f513b25e7).

Subject: 24.5; cl-loop guard clause missing
From: Tino Calancha <[email-masked]>
To: [email-masked]
Date: Thu, 21 Dec 2017 18:38:20 +0900
List-Id: <debbugs-submit.debbugs.gnu.org>

X-Debbugs-CC: [email-masked],[email-masked]

Consider the following snippet code:

--8<-----------------------------cut here---------------start------------->8---
(require 'cl-lib)
(let* ((size 7)
       (arr (make-vector size 0)))
  (cl-loop for k below size
           for x = (* 2 k) and y = (1+ (elt arr k))
           collect (list k x y)))
--8<-----------------------------cut here---------------end--------------->8---

When you execute the form above it fails because
the loop overrun `arr'.

The equivalent code in CL works:
--8<-----------------------------cut here---------------start------------->8---
(let* ((size 7)
       (arr (make-array size :initial-element 0)))
  (loop :for k :below size
           :for x = (* 2 k) :and y = (1+ (elt arr k))
           :collect (list k x y)))
--8<-----------------------------cut here---------------end--------------->8---

* The expansion of `loop' in CL checks the condition
  (>= k 7)
  right before update the internal variables (`x' and `y').

* The expansion of `cl-loop' instead, doesn't check the condition
  before update the vars  =>  in the code above we overrun `arr'.

In GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2017-09-12 on hullmann, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11902000
System Description:	Debian GNU/Linux 9.3 (stretch)