Re: [PATCH v2 5/5] CodingGuidelines: recommend against unportable C99 struct syntax

From: Jeff King <peff@peff.net>
Date: Oct 11, 2022, 00:09 UTC
Message-ID: <Y0S0Tpn/uCjG9J61@coredump.intra.peff.net>
In-Reply-To: <20221010203800.2154698-6-gitster@pobox.com>

On Mon, Oct 10, 2022 at 01:38:00PM -0700, Junio C Hamano wrote:

Show 11 quoted lines

> diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
> index 9598b45f7e..cbe0377699 100644
> --- a/Documentation/CodingGuidelines
> +++ b/Documentation/CodingGuidelines
> @@ -242,6 +242,10 @@ For C programs:
>       printf("%"PRIuMAX, (uintmax_t)v).  These days the MSVC version we
>       rely on supports %z, but the C library used by MinGW does not.
>  
> +   . Shorthand like ".a.b = *c" in struct assignments is known to trip
> +     up an older IBM XLC version, use ".a = { .b = *c }" instead. See
> +     the 33665d98e6b portability fix from mid-2022.

FWIW, the use of the word "assignment" here left me scratching my head. Reading 33665d98e6b, it is about struct initialization.

C99 does allow assignment from a compound literal, like:

  foo = (struct some_struct){ .a = 1, .b = 2 };

but I don't think we have any examples in the current code (and I think we'd consider it a different feature for purposes of testing a weather balloon).

-Peff