Re: [PATCH] xen: Use __auto_type

[Demi Marie Obenour <demiobenour@xxxxxxxxx>]

On 5/12/25 2:25 PM, Elliott Mitchell wrote:
> On Mon, May 12, 2025 at 03:00:18PM +0200, Jan Beulich wrote:
>> On 12.05.2025 14:09, Andrew Cooper wrote:
>>>
>>> Now for the (new) controversial part.  Since sending this, Linux has
>>> decided to just #define auto __auto_type for C < 23, in order to start
>>> writing C23 compatible code from now.  It's more succinct, and has
>>> better longevity.
>>>
>>> We might want to consider the same, although it will introduce a new
>>> example of defining a keyword, which we'd have to call out in the
>>> MISRA/Eclair config.
>>
>> I'm not outright opposed, as I don't think we use "auto" with its
>> original semantics, but it feels somewhat odd.
> 
> Problem is "auto" already has a defined meaning in C.Having this will
> subtly break contributions from authors who weren't familiar with
> everything in Xen's headers.  For anyone who does anything with projects
> besides Xen this will encourage bad habits.
> 
> I believe many projects have a rule of *never* #define C keywords.  I'm
> surprised such made it into the Linux kernel.  I expect it will be ripped
> out in the near future.
> 
> MISRA *doesn't* absolutely forbid this?

I'm no expert on the C standard, but my understanding is that "auto" was
redundant starting in C89, so it is almost entirely unused.  C++11 and later
*do* heavily use "auto", and they use it for roughly the same purpose as C23
does, so I suspect that contributors are far more likely to be familiar with
the C23 "auto" than they are with the pre-C23 version, 
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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