C++ Logo

SG16

Advanced search

Subject: Re: [SG16-Unicode] P1208R3 / source_location
From: Robert Douglas (rwdougla_at_[hidden])
Date: 2019-02-19 18:31:15


So filename and functionname would neccessarily have different encodings?
Does that not seem awful?

On Tue, Feb 19, 2019, 6:25 PM Axel Naumann <Axel.Naumann_at_[hidden]> wrote:

> Thanks everyone, this is what I'll take to Core.
> Axel.
>
> On 19.02.19 13:58, Corentin wrote:
>
> After talking with Tom, I'd like to modify function_name to be a NTMBS as
> it is something we can actually guarantee and I don't think __func__
> should constrain the design of source location. It would consistent with
> thTstatisfy the NB comment (whose resolution was adopted in that direction
> this morning)
>
> Tom convinced me that filename cannot and should not be a NTMBS
>
>
> On Tue, 19 Feb 2019 at 13:22 Robert Douglas <rwdougla_at_[hidden]> wrote:
>
>> Agree.
>>
>> On Tue, Feb 19, 2019 at 5:17 PM Tom Honermann <tom_at_[hidden]> wrote:
>>
>>> On 2/18/19 1:17 PM, Robert Douglas wrote:
>>>
>>> Historical footnote, these are intended to be as drop-in as possible for
>>> existing facilities. __FILE__ is a "character string literal," which gets
>>> it's null termination in phase 7. Since we are accessing these at run-time,
>>> we should thus expect these to be NTBS. Changes to this expectation would
>>> be a deviation from these being a drop-in replacement to __FILE__ and
>>> __func__. Note that [dcl.fct.def.general]
>>> p 8 defines __func__ as an implementation-defined string as if static
>>> const char __func__[] = "function-name "; which implies, also, an NTBS.
>>> This is the reasoning for NTBS. To do otherwise, would deviate this feature
>>> from __FILE__ and __func__, which it is designed to replace.
>>>
>>> Agreed. Certainly guaranteeing that these have a null terminator is
>>> required given that file_name() returns const char*. I don't agree with
>>> associating these with NTMBSs though since multi-byte has encoding
>>> implications.
>>>
>>> Tom.
>>>
>>>
>>>
>>> On Mon, Feb 18, 2019 at 11:20 AM Corentin <corentin.jabot_at_[hidden]>
>>> wrote:
>>>
>>>> Quick reply : display only, no expectation the file can be open, or
>>>> exists, or is a file. It's purely informative. But expectation it can be
>>>> displayed, the main use cases being logging. Otherwise I agree with you.
>>>>
>>>> On Mon, Feb 18, 2019, 7:16 AM Tom Honermann <tom_at_[hidden]> wrote:
>>>>
>>>>>
>>>>> On Feb 18, 2019, at 10:04 AM, Corentin <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]>
>>>>> 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