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Subject: Re: SG16 meeting summary for March 24th, 2021
From: Corentin Jabot (corentinjabot_at_[hidden])
Date: 2021-03-28 15:32:32


On Sun, Mar 28, 2021 at 10:20 PM Alisdair Meredith <alisdairm_at_[hidden]> wrote:

> I’m still not sure I see it. The UB in [lex.phases]p2 is entirely when
> reverting changes
> in raw string literals, and my understanding of this paper is the only raw
> string reversion
> that remains is line splicing, and the presence of the newline character
> means that this
> reversion could never produce a UCN - hence, that particular UB is no
> longer possible
> as its circumstances can no longer occur.
>

\ub \
cd

Can still appear in a source file.
We could/should strike this sentence, but it's still a behavior change
One that affects MSVC. https://godbolt.org/z/xK8j3dM1e

I would be happy if Jens did that in his paper but I think doing it
separately makes sense

>
> I have no issue with the p4 UB moving into the preprocessor clause, merely
> wished to
> highlight it with an editorial note or similar so that it was clear no UB
> was changing,
> merely the place where it is documented is being moved, in the hope of
> avoiding this
> kind of thread in a later discussion ;)
>
> AlisdairM
>
> On Mar 28, 2021, at 3:06 PM, Corentin Jabot <corentinjabot_at_[hidden]>
> wrote:
>
>
>
> On Sun, Mar 28, 2021 at 8:56 PM Alisdair Meredith via SG16 <
> sg16_at_[hidden]> wrote:
>
>> This paper touches, incidentally, wording that is of concern to SG12
>> regarding UB.
>> To ease communication/concerns, it might be worth pointing out the that
>> UB wording
>> added to [lex.concat] is not new UB, but merely moving where we document
>> the
>> existing UB in [lex.phases]p4.
>>
>> As part of this cleanup, is the UB in [lex.phases]p2 still possible, or
>> does the raw
>> remaining string reversion no longer have the ability to accidentally
>> form a UCN as
>> all we are reverting is line-splicing, which implies there must be a
>> new-line character
>> emdedded in any reversion, which would not enable forming a UCN?
>>
>
> There is still UB. While we don't replace unicode by UCNs in phase 1
> anymore, there still may be UCNs spelled in the source.
>
> Removing the UB in lexing is on my radar.
> I think there is consensus that the UB should not be there - and that its
> purpose (dealing with the observability of different models chosen by C and
> C++) is no longer relevant,
> although ideally we would have the same behavior in C and we can confer to
> SG22.
>
>
>>
>> AlisdairM
>>
>> On Mar 28, 2021, at 2:15 PM, Tom Honermann via SG16 <
>> sg16_at_[hidden]> wrote:
>>
>> The summary for the SG16 meeting held March 24th, 2021 is now available.
>> For those that attended, please review and suggest corrections:
>>
>> - https://github.com/sg16-unicode/sg16-meetings#march-24th-2021
>>
>> A decision was made to forward Jens' D2314R2: Character sets and
>> encodings <https://wiki.edg.com/pub/Wg21telecons2021/SG16/d2314r2.html> to
>> EWG at this meeting. Per SG16 operating procedures
>> <https://github.com/sg16-unicode/sg16/blob/master/OperatingProcedures.md>,
>> this decision has tentative consensus as of now and will become the SG16
>> consensus one week from now pending new dissenting perspectives or other
>> new information. Given that the decision was unanimous (though there were
>> abstentions), EWG has already been informed and has tentatively scheduled
>> this paper for discussion on May 6th.
>>
>> *Poll: Forward D2314R2 as presented on 2021-03-24 to EWG for inclusion in
>> C++23.*
>>
>> -
>>
>> Attendance: 9
>> SFFNASA
>> 3 5 0 0 0
>> -
>>
>> Consensus is in favor.
>>
>> Tom.
>> --
>> SG16 mailing list
>> SG16_at_[hidden]
>> https://lists.isocpp.org/mailman/listinfo.cgi/sg16
>>
>>
>> --
>> SG16 mailing list
>> SG16_at_[hidden]
>> https://lists.isocpp.org/mailman/listinfo.cgi/sg16
>
>
>



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