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

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From: Alan Mackenzie <acm <at> muc.de>
To: 67196 <at> debbugs.gnu.org
Subject: bug#67196: 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).

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