GNU bug report logs - #75593
31.0.50; Faulty macro kills Emacs

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Message #35 received at 75593 <at> debbugs.gnu.org (full text, mbox):

From: Pip Cet <pipcet <at> protonmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: ahprae <at> protonmail.com, mattiase <at> acm.org, monnier <at> iro.umontreal.ca,
 75593 <at> debbugs.gnu.org
Subject: Re: bug#75593: 31.0.50; Faulty macro kills Emacs
Date: Thu, 16 Jan 2025 13:06:12 +0000

"Eli Zaretskii" <eliz <at> gnu.org> writes:

>> Date: Thu, 16 Jan 2025 12:08:37 +0000
>> From: Pip Cet <pipcet <at> protonmail.com>
>> Cc: monnier <at> iro.umontreal.ca, mattiase <at> acm.org, ahprae <at> protonmail.com, 75593 <at> debbugs.gnu.org
>>
>> >> (Also, this is not primarily about circular lists, it's about non-lists
>> >> in general).
>> >
>> > That should be easy to detect up front, no?  I thought the issue was
>> > about a cons cell vs a proper list.
>>
>> Sorry, but I don't see a way of checking that we're looking at a proper
>> list that's cheaper that list_length: we need to find the last cons
>> cell, so we need to walk the list, and counting cells while we're doing
>> so should not affect performance.
>
> No, I meant to detect objects that are not CONSP, but something else:
> a number, a symbol, a string, etc.  I thought this was what you meant
> by "non-lists".

Oh, my apologies.  I said "non-list" when what I meant was an "improper
list", in Emacs jargon.  Dotted "lists" caused the crash for the OP;
circular "lists" cause infloops, but no crashes.  The code already
treats !CONSP !NILP objects specially (only Qt as a value is documented,
the rest are silently treated like Qt is).

Pip

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