Re: [PATCH] revision: use C99 declaration of variable in for() loop

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Wed, Nov 17 2021, Phillip Wood wrote:

> Hi Junio
>
> On 15/11/2021 06:27, Junio C Hamano wrote:
>> There are certain C99 features that might be nice to use in our code
>> base, but we've hesitated to do so in order to avoid breaking
>> compatibility with older compilers. But we don't actually know if
>> people are even using pre-C99 compilers these days.
>> One way to figure that out is to introduce a very small use of a
>> feature, and see if anybody complains, and we've done so to probe
>> the portability for a few features like "trailing comma in enum
>> declaration", "designated initializer for struct", and "designated
>> initializer for array".  A few years ago, we tried to use a handy
>>      for (int i = 0; i < n; i++)
>> 	use(i);
>> to introduce a new variable valid only in the loop, but found that
>> some compilers we cared about didn't like it back then.  Two years
>> is a long-enough time, so let's try it agin.
>> If this patch can survive a few releases without complaint, then we
>> can feel more confident that variable declaration in for() loop is
>> supported by the compilers our user base use.  And if we do get
>> complaints, then we'll have gained some data and we can easily
>> revert this patch.
>
> I like the idea of using a specific test balloon for the features that
> we want to use but wont this one break the build for anyone doing
> 'make DEVELOPER=1' because -Wdeclaration-after-statement will error
> out. I think we could wrap the loop in gcc's warning pragmas to avoid
> that.

Good point.

Overall something that brings us to the end-state 765dc168882
(git-compat-util: always enable variadic macros, 2021-01-28) brought us
to is probably better, i.e. something you can work around by defining or
undefining a macro via a Makefile parameter, instead of needing to patch
git's sources.