Subject: Re: bug#75964: Switching the Emacs build to -Wswitch-enum in src/

From: Pip Cet <[email-masked]>
Date: Sun, 02 Feb 2025 16:51:30 +0000

"Eli Zaretskii" <[email-masked]> writes:

>> Date: Sun, 02 Feb 2025 12:50:15 +0000
>> From: Pip Cet <[email-masked]>
>> Cc: [email-masked], [email-masked], [email-masked], Andrea Corallo <[email-masked]>, Stefan Monnier <[email-masked]>
>>
>> "Eli Zaretskii" <[email-masked]> writes:
>>
>> > We (should) use emacs_abort when the code has no way of dealing with
>> > some situation, so letting the execution continue past that point will
>> > sometimes crash or corrupt data in ways that are much harder to debug
>> > than an abort.
>>
>> We often use eassert for that, and I don't know how many people realize
>> this subtle difference between emacs_abort () and eassert (0).
>
> Well, I do: eassert compiles to nothing in a production build, so it
> is only okay if the code can do something with the situation, albeit
> something that will cause weird effects.  eassert is also appropriate
> to convey the assumptions made by the code, even if no trouble will be
> caused by violating those assumptions.

Interesting.  I often use eassert where the only thing we can do in a
production build is almost certainly a crash.  Can you say more about
cases in which it's used to avoid crashes?

>> I still think eassume and eassert shouldn't evaluate expressions with
>> side effects.
>
> I agree.  Do we have code which does that in Emacs?

I'm aware of

      eassert (check_comp_unit_relocs (comp_u));

in comp.c, which does call an extra function, which might in theory have
side effects because dynlib_sym or Flength or, God forbid, Fgethash may
develop some.  But, really, this is a special case and a very minor
issue.

Pip