GNU bug report logs - #62847
29.0.90; Propertized space in Org Agenda's mode-name

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Package: emacs;

Reported by: Gustavo Barros <gusbrs.2016 <at> gmail.com>

Date: Fri, 14 Apr 2023 23:05:02 UTC

Severity: normal

Found in version 29.0.90

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Message #47 received at 62847 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Ihor Radchenko <yantar92 <at> posteo.net>, 62847 <at> debbugs.gnu.org,
 Stefan Monnier <monnier <at> iro.umontreal.ca>, gusbrs.2016 <at> gmail.com
Subject: Re: bug#62847: 29.0.90; Propertized space in Org Agenda's mode-name
Date: Sat, 15 Apr 2023 15:15:12 +0200

15 apr. 2023 kl. 13.45 skrev Eli Zaretskii <eliz <at> gnu.org>:
>>> So maybe replace " " with (copy-sequence " ").
>> 
>> But that should not be necessary, right?

Ideally not -- setting properties on literal strings should indeed be avoided for a variety of reasons, one being that the byte compiler shares equal string literals:

(defun ff ()
  (list "abc" (let ((s "abc"))
                (put-text-property 0 3 'aa 'bb s)
                s)))

(ff)
 -> ("abc" #("abc" 0 3 (aa bb)))                 ; interpreted
 -> (#("abc" 0 3 (aa bb)) #("abc" 0 3 (aa bb)))  ; byte-compiled

`org-agenda-set-mode-name` uses the literal " " twice so if either is modified the other will appear to be, too. Where this setting of properties is done I have no idea

There is currently no automatic sharing of string literals between byte-code functions but this may change, and I've no idea what the native compiler is up to in this respect.

`propertize` is safe because it makes a copy of its string argument, so there shouldn't be any reason to copy that argument explicitly.

`org-add-props` calls `add-text-properties` and is clearly destructive.

Interpreted code is less affected by the problem because literals aren't shared throughout a function, but trouble can still occur:

(defun hh (x)
  (let ((s "abc"))
    (when x
      (put-text-property 0 3 'aa 'bb s))
    s))

(hh nil) -> "abc"
(hh t)   -> #("abc" 0 3 (aa bb))
(hh nil) -> #("abc" 0 3 (aa bb))
...
This bug report was last modified 2 years and 64 days ago.

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