GNU bug report logs - #55205
28.1.50; completion--replace illegally mutates completion candidates

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Daniel Mendler <mail <at> daniel-mendler.de>
Subject: bug#55205: closed (Re: bug#55205: 28.1.50; completion--replace
 illegally mutates completion candidates)
Date: Fri, 29 Nov 2024 18:00:03 +0000

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Your bug report

#55205: 28.1.50; completion--replace illegally mutates completion candidates

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 55205 <at> debbugs.gnu.org.

-- 
55205: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=55205
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Daniel Mendler <mail <at> daniel-mendler.de>
To: 55205-done <at> debbugs.gnu.org
Subject: Re: bug#55205: 28.1.50; completion--replace illegally mutates
 completion candidates
Date: Fri, 29 Nov 2024 18:59:27 +0100

Fixed in 29.

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From: Daniel Mendler <mail <at> daniel-mendler.de>
To: bug-gnu-emacs <at> gnu.org
Cc: Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: 28.1.50; completion--replace illegally mutates completion candidates
Date: Sun, 1 May 2022 10:27:56 +0200

The function completion--replace mutates the replacement string, it
strips the text properties. The command minibuffer-force-complete calls
(completion--replace base end (car all)) on the first candidate returned
by completion-all-sorted-completions, which then affects the candidate
strings passed to completing-read. The candidate strings passed to
completing-read should be treated as constant and should not be mutated.

There are two possibilities to fix this:

1. Copy the string (with concat or substring) before mutating it in
completion--replace. This is the preferred solution and will make
completion--replace safer to use.
2. Copy the candidate string just before passing it to
completion--replace. This is the approach I take for example in my Corfu
package and I will continue to do so for backward compatibility. Still,
the pattern is error prone and copying the candidate string is easily
forgotten, (completion--replace beg end (concat cand)).

Original downstream issue: https://github.com/minad/consult/issues/566

In GNU Emacs 28.1.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
version 1.16.0, Xaw scroll bars)
 of 2022-04-29 built on projects
Repository revision: 3b6338c8c351cce721f2f1aa115cadc401179d5c
Repository branch: emacs-28
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

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