GNU bug report logs - #56201
Backtrace fails to appear in an error situation.

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: bug-gnu-emacs <at> gnu.org
Subject: Backtrace fails to appear in an error situation.
Date: Fri, 24 Jun 2022 17:42:37 +0000

Hello, Emacs.

(i) With the master branch, start Emacs (-Q not needed). 
(ii) Visit a non-empty file in a buffer.
(iii) M-s o <regexp that will generate matches>.
(iv) C-x o to move to the *Occur* buffer.
(v) Move point to somewhere in the displayed matches.
(vi) C-x C-q to swith off read-onliness.
(vii) C-j, an attempt to insert a newline.

This produces the error message "Text is read-only".  This is probably a
bug, but is minor compared to what follows:

(viii) M-: (setq debug-on-error t) RET.
(ix) C-j.

This ought to produce a backtrace, but doesn't.  It merely repeats the
error message "Text is read-only".  This is a major bug; how can one
solve minor bugs if attempts to get diagnostic information are blocked?

It would appear a frivolous condition-case is discarding the backtrace
here.  This appears to happen with lots of error messages.  This is not
a Good Thing.

-- 
Alan Mackenzie (Nuremberg, Germany).

Message #8 received at 56201 <at> debbugs.gnu.org (full text, mbox):

From: Andreas Schwab <schwab <at> linux-m68k.org>
To: Alan Mackenzie <acm <at> muc.de>
Cc: 56201 <at> debbugs.gnu.org
Subject: Re: bug#56201: Backtrace fails to appear in an error situation.
Date: Fri, 24 Jun 2022 20:22:26 +0200

See debug-ignored-errors.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Message #11 received at 56201 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Alan Mackenzie <acm <at> muc.de>
Cc: 56201 <at> debbugs.gnu.org
Subject: Re: bug#56201: Backtrace fails to appear in an error situation.
Date: Fri, 24 Jun 2022 20:23:23 +0200

Alan Mackenzie <acm <at> muc.de> writes:

> This ought to produce a backtrace, but doesn't.  It merely repeats the
> error message "Text is read-only".  This is a major bug; how can one
> solve minor bugs if attempts to get diagnostic information are blocked?

There's a lot of error conditions that are "normal" and handled by the
code, and `debug-on-error' doesn't help you with that.  You have to set
`debug-on-signal' to get a backtrace from those.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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