GNU bug report logs - #67196
M-: uses a wrong value of debug-on-error when it is nil.

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Alan Mackenzie <acm <at> muc.de>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#67196: closed (M-: uses a wrong value of debug-on-error when
 it is nil.)
Date: Thu, 24 Oct 2024 21:35:02 +0000

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Your message dated Thu, 24 Oct 2024 21:33:41 +0000
with message-id <Zxq9NZDAap-fzctO <at> MAC.fritz.box>
and subject line Re: M-: uses a wrong value of debug-on-error when it is nil.
has caused the debbugs.gnu.org bug report #67196,
regarding M-: uses a wrong value of debug-on-error when it is nil.
to be marked as done.

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


-- 
67196: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=67196
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Alan Mackenzie <acm <at> muc.de>
To: bug-gnu-emacs <at> gnu.org
Subject: M-: uses a wrong value of debug-on-error when it is nil.
Date: Wed, 15 Nov 2023 13:48:40 +0000

Hello, Emacs.

On the master branch (and probably any recent Emacs):

(i) emacs -Q
(ii) C-h v debug-on-error RET
(iii) M-: debug-on-error RET

From (ii) it will be seen that debug-on-error's value is nil.
(iii) wrongly reports that its value is t.  This is a bug.

#########################################################################

What is happening here is that eval-expression binds debug-on-error to
an uninterned symbol called "t", so that d-o-e will be set to non-nil
for the evaluation of the coming form.

This has the unwanted side effect of ignoring the actual value of d-o-e
in forms which use it.  For example, if the variable is set to a list of
error symbols, this value gets ignored on evaluating a form with M-:.

-- 
Alan Mackenzie (Nuremberg, Germany).

[Message part 3 (message/rfc822, inline)]

From: Alan Mackenzie <acm <at> muc.de>
To: 67196-done <at> debbugs.gnu.org
Cc: acm <at> muc.de
Subject: Re: M-: uses a wrong value of debug-on-error when it is nil.
Date: Thu, 24 Oct 2024 21:33:41 +0000

On Wed, Nov 15, 2023 at 13:48:40 +0000, Alan Mackenzie wrote:
> Hello, Emacs.

> On the master branch (and probably any recent Emacs):

> (i) emacs -Q
> (ii) C-h v debug-on-error RET
> (iii) M-: debug-on-error RET

> From (ii) it will be seen that debug-on-error's value is nil.
> (iii) wrongly reports that its value is t.  This is a bug.

> #########################################################################

> What is happening here is that eval-expression binds debug-on-error to
> an uninterned symbol called "t", so that d-o-e will be set to non-nil
> for the evaluation of the coming form.

> This has the unwanted side effect of ignoring the actual value of d-o-e
> in forms which use it.  For example, if the variable is set to a list of
> error symbols, this value gets ignored on evaluating a form with M-:.

This bug was fixed by the following commit:

commit 7959a63ce258c90eb3c7947ab3318c5531eb37d9
Author: Stefan Monnier <monnier <at> iro.umontreal.ca>
Date:   Mon Dec 18 23:47:56 2023 -0500

    (eval-expression): Fix bug#67196

by using the newly written handler-bind.

-- 
Alan Mackenzie (Nuremberg, Germany).

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