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bug#38812: 28.0.50; Custom: Problem with reverting some session's custom
From: |
Eli Zaretskii |
Subject: |
bug#38812: 28.0.50; Custom: Problem with reverting some session's customizations |
Date: |
Tue, 31 Dec 2019 19:25:23 +0200 |
> From: Mauro Aranda <maurooaranda@gmail.com>
> Date: Tue, 31 Dec 2019 14:21:09 -0300
> Cc: 38812@debbugs.gnu.org
>
> > And I have a question: isn't it better not to use setcar in
> > custom-push-theme instead?
>
> I thought of doing that, and use setf with alist-get to make the change
> instead. But I think we'll be better off if we avoid sharing the cons
> cell inadvertedly, since that is prone to have bugs like this one.
And I actually think that a problem should be fixed where it is
caused. There's nothing wrong per se with sharing portions of Lisp
data structures.
> Alternatively, we could create the list in custom-theme-recalc-variable,
> to accomplish the same thing without changing the return value of
> custom-variable-theme-value. In that case, I think it would be
> convenient to change the doc string of custom-variable-theme-value, to
> say it returns some cdr.
>
> To me, either the patch I posted (with an additional explanatory
> comment, of course) or the latter option sound better, but I won't argue
> too much if you think otherwise.
My alternative patch is below. WDYT?
diff --git a/lisp/custom.el b/lisp/custom.el
index 26bdaae2c2..7ed85b22e8 100644
--- a/lisp/custom.el
+++ b/lisp/custom.el
@@ -886,7 +886,10 @@ custom-push-theme
(put theme 'theme-settings
(cons (list prop symbol theme value)
(delq res theme-settings)))
- (setcar (cdr setting) value)))
+ ;; It's tempting to use setcar here, but that could
+ ;; inadvertently modify other properties in SYMBOL's proplist,
+ ;; if those just happen to share elements with the value of PROP.
+ (put symbol prop (cons (list theme value) (delq setting old)))))
;; Add a new setting:
(t
(when (custom--should-apply-setting theme)