Re: [PATCH] compat/posix.h: enable UNUSED warning messages for Clang

[Junio C Hamano <gitster@pobox.com>]

Dominik Loidolt <dominik.loidolt@univie.ac.at> writes:

> Treat Clang like GCC 4.5+ so using an UNUSED parameter emits the
> intended warning message.
>
> Commit 7c07f36ad2 (git-compat-util.h: GCC deprecated message arg only in
> GCC 4.5+, 2022-10-05) restricted use of the deprecated attribute's
> message argument in the UNUSED macro to GCC 4.5 or newer.
>
> Clang identifies itself as GNUC 4.2.1 for compatibility, causing the
> current check to use the deprecated attribute without a message, even
> though Clang supports deprecated("...") since version 2.9 (2011).
>
> Signed-off-by: Dominik Loidolt <dominik.loidolt@univie.ac.at>
> ---
> I am not familiar with git's minimum compiler version but this patch
> drops support for Clang < 2.9 from 2011.

Does this "drop support" because you force _all_ versions of Clang
to use the "deprecated" attribute, even though you _know_ some older
versions do not understand it?  Don't these versions identify
themselves so that you can do

	#if defined(__clang__) && CLANG_VERSION >= 2.9

I do not know if the userbase of GCC and Clang upgrade with a
similar cadence, or we seem to say that we care about GCC 4.5
(2010), so giving  a similar version detection for Clang and exclude
ones older than 2.9 sounds more appropriate.

> Dominik
> P.S. This is my first patch sent by email. Please let me know if I
> missed something.
>
>  compat/posix.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/compat/posix.h b/compat/posix.h
> index 245386fa4a..ed83a4d9d4 100644
> --- a/compat/posix.h
> +++ b/compat/posix.h
> @@ -35,7 +35,7 @@
>   * When a parameter may be used or unused, depending on conditional
>   * compilation, consider using MAYBE_UNUSED instead.
>   */
> -#if GIT_GNUC_PREREQ(4, 5)
> +#if GIT_GNUC_PREREQ(4, 5) || defined(__clang__)
>  #define UNUSED __attribute__((unused)) \
>  	__attribute__((deprecated ("parameter declared as UNUSED")))
>  #elif defined(__GNUC__)
>
> base-commit: 67ad42147a7acc2af6074753ebd03d904476118f
> --
> 2.54.0