C++ Logo

SG16

Advanced search

Subject: Re: [SG16-Unicode] P1208R3 / source_location
From: Axel Naumann (Axel.Naumann_at_[hidden])
Date: 2019-02-18 11:51:49


Hi Tom,

> In San Diego, the guidance we gave for the stacktrace proposal is that
> file names are implementation defined bags-of-bytes.

How does that compare to

>> "Specify that the strings are
>> first formed using the basic source character set (with
>> universal-character-names as necessary) then mapped in the manner
>> applied to string literals with no encoding prefix in phases 5
>> and 6 oftranslation."

Or in other words, what does the wording look like for SG16's guidance?

Axel.

On 18.02.19 07:16, Tom Honermann wrote:
>
> On Feb 18, 2019, at 10:04 AM, Corentin <corentin.jabot_at_[hidden]
> <mailto:corentin.jabot_at_[hidden]>> wrote:
>
>>
>> Very good points. 
>> Wouldn't it be sufficient to specify that the strings are NTMBS
>> encoded using the execution character set?
>> source_location currently avoids making any assumption about how these
>> strings are formed, including that they are derived from a source file.
>> So since the value is implementation-defined, so should be the way
>> it's constructed. 
>> However, it is reasonable to assume that these things are valid text
>> and therefore have a known encoding.
>>
>> Adding Tom, because this is borderline SG16 territory. 
>
> This isn’t borderline as we have (recently) requested review of anything
> involving file names. 
>
>>
>>
>> @Tom: Do you want to see source_location this week knowing that I'd
>> hope it would get through LWG before the end of the week?
>> Or do you think having function_name / filename as multi-bytes strings
>> encoded using the execution character set is reasonable?
>> The alternative I see are
>>
>> * Leave it unspecified
>> * Force a specific character set... which the world is not ready for
> I think there is a higher level question to answer. Are the provided
> file names display only, or should one expect to be able to open the
> file using the provided name?
>
> If they are display only, then we can specify an encoding for them
> similarly to what is done for member functions of std::filesystem::path.
> In this case, we must explicitly acknowledge that the names do not
> roundtrip through the filesystem (though typically will in practice).
> Note that, on Windows, file names cannot be represented accurately using
> char based strings, so unless we want to add wchar_t support, these
> names will be technically display only. 
>
> If they are potentially not display only, then we can’t associate an
> encoding and the names are bags-of-bytes. This is a limitation of POSIX.
> But then we need wchar_t support for Windows. 
>
> In San Diego, the guidance we gave for the stacktrace proposal is that
> file names are  implementation defined bags-of-bytes. If we advised
> otherwise for source location, we would be giving inconsistent guidance. 
>
> I think we should discuss this in SG16 this week. Not necessarily to
> propose changes for the proposal, but to solidify our collective
> thinking around file names. 
>
> Tom. 
>>
>> Thanks, 
>> Corentin
>>
>>
>>
>> On Mon, 18 Feb 2019 at 03:56 Axel Naumann <Axel.Naumann_at_[hidden]
>> <mailto:Axel.Naumann_at_[hidden]>> wrote:
>>
>> Hi Robert,
>>
>> Regarding your P1208R3:
>>
>> Nit: it's titled "D1208R3", it doesn't mention email addresses.
>>
>> Not-so-nit: a NB comment on the reflection TS asks to not use NTBS but
>> NTMBS and "Where NTBS is mentioned in the document under ballot, the
>> encoding used for the string’s value is unspecified." Jens agrees that
>> the proposed solution should be applied: "Specify that the strings are
>> first formed using the basic source character set (with
>> universal-character-names as necessary) then mapped in the manner
>> applied to string literals with no encoding prefix in phases 5 and
>> 6 of
>> translation."
>>
>> I would very much hope that both changes are also applied to
>> P1208R3. I
>> call this out explicitly in our recommended NB comment response paper.
>>
>> Cheers, Axel.
>>


SG16 list run by herb.sutter at gmail.com