Re: [PATCH 2/3] ci: add build checking for side-effects in assert() calls

From: Elijah Newren <newren@gmail.com>
Date: Mar 14, 2025, 01:27 UTC
Message-ID: <CABPp-BHRSnNE0zj9kRjrVm4-NXt33tYBT_iSgZU-5JU9Y2vp3w@mail.gmail.com>
In-Reply-To: <xmqqtt7wl85l.fsf@gitster.g>

On Thu, Mar 13, 2025 at 6:20 PM Junio C Hamano <gitster@pobox.com> wrote:

Show 18 quoted lines

>
> "brian m. carlson" <sandals@crustytoothpaste.net> writes:
>
> >> Is this something we can use in our project?  I am just double
> >> checking.
> >
> > I believe it's valid in C99.  Certainly some compiler might be bad at
> > optimizing, or a user may have compiled with -O0, but this is run in CI,
> > where we have known good compilers and can control the optimization
> > flags.  I doubt GCC, Clang, or MSVC will have problems here, and since
> > this is not on by default, users using something less capable (the Tiny
> > C Compiler, maybe?) or a vendor compiler won't even see it.
> >
> > Was there some other case that you were concerned about?
>
> Licensing, mostly, as clever things we see are not necessarily home
> grown.  I know the patch came with DCO sign-off, but it does not
> hurt to double check.

These two lines:

> +extern int not_supposed_to_survive;
> +#define assert(expr) ((void)(not_supposed_to_survive || (expr)))

, which serve as the core trick, I had used elsewhere before. Doing some searches, it looks like those likely came from https://stackoverflow.com/questions/10593492/catching-assert-with-side-effects. And it appears that StackOverflow is CC-BY-SA-3.0 or -4.0. Doh, sorry. Anyone got a clever alternative?

The rest of the patch was all written by me.