Re: [PATCH] config.mak.dev: enable -Wunreachable-code

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 7, 2025, 23:28 UTC
Message-ID: <xmqqzfhwbev1.fsf@gitster.g>
In-Reply-To: <20250307225444.GA42758@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

> I was disappointed that the compiler didn't complain, though. Maybe we
> should do this:

Indeed.  It would have helped us if it were already there in place.

Show 17 quoted lines

> -- >8 --
> Subject: [PATCH] config.mak.dev: enable -Wunreachable-code
>
> Having the compiler point out unreachable code can help avoid bugs, like
> the one discussed in:
>
>   https://lore.kernel.org/git/20250307195057.GA3675279@coredump.intra.peff.net/
>
> In that case it was found by Coverity, but finding it earlier saves
> everybody time and effort.
>
> We can use -Wunreachable-code to get some help from the compiler here.
> Interestingly, this is a noop in gcc. It was a real warning up until gcc
> 4.x, when it was removed for being too flaky, but they left the
> command-line option to avoid breaking users. See:
>
>   https://stackoverflow.com/questions/17249934/why-does-gcc-not-warn-for-unreachable-code

Wow, now they leave their users confused, making them wondering why their command line option does not do anything useful ;-)

> However, clang does implement this option, and it finds the case
> mentioned above (and no other cases within the code base). And since we
> run clang in several of our CI jobs, that's enough to get an early
> warning of breakage.

Yes, this is great.

Thanks.