We have issues even with GCC - it doesn't work reliably, because mtime
precision differs between filesystems, and so you end up with differing
mtimes for the same file.

On Tue, Aug 27, 2024 at 5:25 PM Jeremy Rifkin <rifkin.jer_at_[hidden]> wrote:

> Hi,
> Thank you for your comments.
>
> > #pragma once is unimplementable.
>
> Every notable C/C++ compiler has implemented it.
>
> > That's because it doesn't mean "don't include a file with the same
> bytes"
>
> On GCC it more or less does.
>
> > And the second you have the same file accessible through two separate
> fuse mountpoints, no amount of stat() will help you identify it's the same
> file.
>
> This proposal does not propose any use of stat() for determining file
> identity. I understand concerns regarding paths, links, and mounts and have
> taken care in this proposal to propose a robust solution. This solution
> proposed here should not cause problems in cases you refer to with your
> build farms. If you can think of a way it would, I would be interested.
>
> Cheers
> Jeremy
>
> On Tue, Aug 27, 2024 at 10:34 Gašper Ažman via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
>> #pragma once is unimplementable.
>>
>> That's because it doesn't mean "don't include a file with the same
>> bytes", it means "don't include the same file". And the second you have the
>> same file accessible through two separate fuse mountpoints, no amount of
>> stat() will help you identify it's the same file.
>>
>> We hit this in our build-farms all the time, I had to write tooling to
>> kill it.
>>
>> Don't make me explain this in-committee, again.
>>
>> On Tue, Aug 27, 2024 at 4:32 PM Tiago Freire via Std-Proposals <
>> std-proposals_at_[hidden]> wrote:
>>
>>> I like pragma once, should be standardized, but the problem is in the
>>> details of the wording.
>>>
>>> I know that the paper acknowledges that some compiler issues a warning
>>> if they appear in the source file, and that the paper doesn't advocate for
>>> the warning either way. But the note seems to suggest otherwise.
>>> It would be best if the standard had no notion of what a source file is,
>>> and you should remove the note that a compiler could issue a warning, let
>>> that just be a vendor detail.
>>>
>>> The description of how the directive should behave isn't the best,
>>> describing in in terms of an ifdef block is not good.
>>>
>>>
>>> ------------------------------
>>> *From:* Std-Proposals <std-proposals-bounces_at_[hidden]> on
>>> behalf of Jeremy Rifkin via Std-Proposals <
>>> std-proposals_at_[hidden]>
>>> *Sent:* Tuesday, August 27, 2024 4:01:08 PM
>>> *To:* Jeremy Rifkin via Std-Proposals <std-proposals_at_[hidden]>
>>> *Cc:* Jeremy Rifkin <rifkin.jer_at_[hidden]>
>>> *Subject:* [std-proposals] Revising #pragma once
>>>
>>> Hi,
>>> I have drafted a proposal for standardizing #pragma once. This has been
>>> previously proposed a few years ago and I recognize that on top of being
>>> difficult to standardize, existing opinions on this topic may render the
>>> paper dead on arrival. However, due to its widespread nature and concerns
>>> about portability contributing to it not being used more I think it's worth
>>> revisiting. I have uploaded the first draft at:
>>> https://jeremy-rifkin.github.io/cpp-proposals/drafts/pragma-once-draft-1.html
>>> .
>>>
>>> Cheers,
>>> Jeremy
>>> --
>>> Std-Proposals mailing list
>>> Std-Proposals_at_[hidden]
>>> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>>>
>> --
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>>
>