Subject: Re: [PATCH] CodingGuidelines: give deadline for "for (int i = 0; ..."

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Thu, 31 Mar 2022 16:58:07 +0200

On Thu, Mar 31 2022, Phillip Wood wrote:

> On 31/03/2022 11:10, Ævar Arnfjörð Bjarmason wrote:
>> On Wed, Mar 30 2022, Junio C Hamano wrote:
>> 
>>> We raised the weather balloon to see if we can allow the construct
>>> in 44ba10d6 (revision: use C99 declaration of variable in for()
>>> loop, 2021-11-14), which was shipped as a part of Git v2.35.
>>> Document that fact in the coding guidelines, and more importantly,
>>> give ourselves a deadline to revisit and update.
>>>
>>> Let's declare that we will officially adopt the variable declaration
>>> in the initializaiton [...]
>> Typo: initialization.
>> 
>>> part of "for ()" statement this winter, unless we find that a platform
>>> we care about does not grok it.
>> I'd think that waiting a couple of releases would be sufficient for
>> this
>> sort of thing. I.e. contributors to this project already have
>> access/knowledge about a wide variety of compilers, especially the
>> "usual suspects" (mainly MSVC) that have been blockers for using new
>> language features in the past.
>> So I'm in no rush to use this, and the winter deadline sounds fine
>> to
>> me in that regard.
>
> Agreed, I think it is worth waiting so we don't get into a situation
> where we end up having to revert changes that are using the new
> features because we discover they are not supported by a platform we
> care about.
>
>> But on the other hand I think the likelihood that waiting until November
>> v.s. May revealing that a hitherto unknown compiler or platform has
>> issues with a new language feature is vanishingly small.
>> 
>>> A separate weather balloon for C99 as a whole was raised separately
>>> in 7bc341e2 (git-compat-util: add a test balloon for C99 support,
>>> 2021-12-01).  Hopefully, as we find out that all C99 features are OK
>>> on all platforms we care about, we can stop probing the features we
>>> want one-by-one like this
>> Unfortunately this really isn't the case at all, the norm is for
>> compilers to advertise that they support verison X of the standard via
>> these macros when they consider the support "good enough", but while
>> there's still a long list of unimplemented features before they're at
>> 100% support (and most never fully get to 100%).
>> We also need to worry about the stdlib implementation, and not just
>> the
>> compiler, see e.g. the %zu format and MinGW in the exchange at
>> https://lore.kernel.org/git/[email-masked]/
>> and
>> https://lore.kernel.org/git/[email-masked]/;
>
> That's a good point, it was a surprise to me that the problem is with
> MinGW rather than MSVC.

Yes, thanks a lot for tracking that down.

I wonder if we can supply a compatibility sprintf() shim for that setup,
there's nothing urgent about it, but the verbosity of the casts and
PRIuMAX inline adds up, especially as we've started using size_t more
widely:

	git grep PRIuMAX -- '*.[ch]'

Either by e.g. grabbing the sprintf() shim from say gnulib, or our own
shim that would intercept the "const char *format" for sprintf(), and
pull a trick similar to what we do in strbuf_addftime() to rewrite the
format (of a copied string) on-the-fly.