GNU bug report logs - #29799
24.5; cl-loop guard clause missing

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Tino Calancha <tino.calancha <at> gmail.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#29799: closed (24.5; cl-loop guard clause missing)
Date: Mon, 08 Jan 2018 10:21:01 +0000

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Your message dated Mon, 08 Jan 2018 19:20:35 +0900
with message-id <87r2r0ird8.fsf <at> gmail.com>
and subject line Re: bug#29799: 24.5; cl-loop guard clause missing
has caused the debbugs.gnu.org bug report #29799,
regarding 24.5; cl-loop guard clause missing
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
29799: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=29799
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From: Tino Calancha <tino.calancha <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.5; cl-loop guard clause missing
Date: Thu, 21 Dec 2017 18:38:20 +0900

X-Debbugs-CC: monnier <at> iro.umontreal.ca,npostavs <at> gmail.com

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)

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From: Tino Calancha <tino.calancha <at> gmail.com>
To: 29799-done <at> debbugs.gnu.org
Subject: Re: bug#29799: 24.5; cl-loop guard clause missing
Date: Mon, 08 Jan 2018 19:20:35 +0900

Noam Postavsky <npostavs <at> users.sourceforge.net> writes:

> Tino Calancha <tino.calancha <at> gmail.com> 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).

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