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<div class="moz-cite-prefix">On 8/13/19 8:35 AM, Corentin Jabot
wrote:<br>
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<div dir="ltr">Chiming in with my favorite solution:<br>
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<li>Forbid lossy source -> presumed execution encoding
conversion (all ready ill formed in gcc but not msvc)</li>
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I think this may be reasonable.<br>
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<li>Forbid u8/u16/u32 literals in non unicode encoded files</li>
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I don't understand this at all. u8/u16/u32 specify the encoding to
be used at run-time. The source file encoding isn't relevant at all
(as Steve noted, source file characters are converted to internal
encoding).<br>
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<li>Expose the "presumed execution encoding" (= "narrow/wide
character literal encoding") as a consteval function
returning the name as specified by iana <a
href="https://www.iana.org/assignments/character-sets/character-sets.txt"
moz-do-not-send="true">https://www.iana.org/assignments/character-sets/character-sets.txt</a></li>
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This may be useful, but needs more justification (preferably in the
form of a paper).<br>
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<div>I would expect changing the encoding of char would break
everything... I'd leave char and wchar_t mostly alone and
start clean on char8_t.</div>
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I agree, but I don't think that will be suffiicent. Not all
projects are going to adopt char8_t. A substantial portion,
especially on Linux/UNIX systems will choose to continue use of
UTF-8 using char. I think we're going to have to provide Unicode
support for char and char8_t (and char16_t, and perhaps char32_t).<br>
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<div>Anyhow, I agree with Tom that the names are not
indicative</div>
<div>How about: "narrow/wide character literal encoding" ?</div>
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<p>"execution encoding" has a long history in both WG14 and WG21
(though not POSIX I think) and that makes me reluctant to try and
challenge it. In Slack, discussion, I think Steve Downey probably
hit on the right approach; provide a formal definition of it. I
think we *might* be successful in using "execution encoding" to
apply to both the compile-time and run-time encodings by extending
the term with specific qualifiers; e.g., "presumed execution
encoding" and "run-time/system/native execution encoding".<br>
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<p>Tom.<br>
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<div dir="ltr" class="gmail_attr">On Tue, 13 Aug 2019 at
10:39, Niall Douglas <<a
href="mailto:s_sourceforge@nedprod.com"
moz-do-not-send="true">s_sourceforge@nedprod.com</a>>
wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">Before progressing with a
solution, can I ask the question:<br>
<br>
Is it politically feasible for C++ 23 and C 2x to require<br>
implementations to default to interpreting source files as
either (i) 7<br>
bit ASCII or (ii) UTF-8? To be specific, char literals would
thus be<br>
either 7 bit ASCII or UTF-8.<br>
<br>
(The reason for the 7 bit ASCII is that it is a perfect
subset of UTF-8,<br>
and that C very much wants to retain the language being
implementable in<br>
a small code base i.e. without UTF-8 support. Note the
qualifier<br>
"default" as well)<br>
<br>
An answer to the above would determine how best to solve
your issue Tom,<br>
I think. As much as we all expect IBM et al to veto such a
proposal, one<br>
never gets anywhere without asking first.<br>
<br>
Niall<br>
<br>
On 13/08/2019 03:25, Tom Honermann wrote:<br>
> I agree with this (mostly), but would prefer not to
discuss further in<br>
> this thread. The only reason I included the filesystem
references is<br>
> because the wording there uses "native" for an encoding
that is related<br>
> (though distinct) from the encodings referenced in the
codecvt and ctype<br>
> wording, where "native" is also used. This suggests
that "native"<br>
> serves (or should serve) a role in naming these
run-time encodings, or<br>
> is a source of conflation (or both).<br>
> <br>
> Tom.<br>
> <br>
> On 8/12/19 5:08 PM, Niall Douglas wrote:<br>
>>> 1. [fs.path.type.cvt]p1 <<a
href="http://eel.is/c++draft/fs.path.type.cvt#1"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://eel.is/c++draft/fs.path.type.cvt#1</a>>:<br>
>>> (though the definition provided here
appears to be specific to path<br>
>>> names).<br>
>>> "The /native encoding/ of an ordinary
character string is the<br>
>>> operating system dependent current
encoding for path names. The<br>
>>> /native encoding/ for wide character
strings is the<br>
>>> implementation-defined execution
wide-character set encoding."<br>
>> We discussed the problems with the choice of
normative wording in<br>
>> <a
href="http://eel.is/c++draft/fs.class.path#fs.path.cvt"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://eel.is/c++draft/fs.class.path#fs.path.cvt</a>,
if you remember,<br>
>> during SG16's discussion of filesystem::path_view.<br>
>><br>
>> The problem is that filesystem paths have different
encoding and<br>
>> interpretation per-path-component i.e. for a path<br>
>><br>
>> /A/B/C/D<br>
>><br>
>> ... A, B, C and D may each have its own,
individual, encoding and<br>
>> interpretation depending on the mount points and
filesystems configured<br>
>> on the current system. This is not what is
suggested by the current<br>
>> normative wording, which appears to think that some
mapping exists<br>
>> between C++ paths and OS kernel paths.<br>
>><br>
>> There *is* a mapping, but it is 100% C++-side. The
OS kernel generally<br>
>> consumes arrays of bytes.<br>
>><br>
>> A more correct normative wording would more clearly
separate these two<br>
>> kinds of path representation. OS kernel paths are
arrays of `byte`, but<br>
>> with certain implementation-defined byte sequences
not permitted. C++<br>
>> paths can be in char, wchar_t, char8_t, char16_t,
char32_t etc, and<br>
>> there are well defined conversions between those
C++ paths and the array<br>
>> of bytes supplied to the OS kernel. The standard
can say nothing useful<br>
>> about how the OS kernel may interpret the byte
array C++ supplies to it.<br>
>><br>
>> If path_view starts the standards track, I'll need
to propose a document<br>
>> fixing up <a
href="http://eel.is/c++draft/fs.class.path#fs.path.cvt"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://eel.is/c++draft/fs.class.path#fs.path.cvt</a>
in any case.<br>
>> But to come back to your original question, I think
that you ought to<br>
>> split off filesystem paths from everything else,
consider them separate,<br>
>> and then I think you'll find it much easier to make
the non-path<br>
>> normative wording more consistent.<br>
>><br>
>> Niall<br>
>> _______________________________________________<br>
>> SG16 Unicode mailing list<br>
>> <a href="mailto:Unicode@isocpp.open-std.org"
target="_blank" moz-do-not-send="true">Unicode@isocpp.open-std.org</a><br>
>> <a
href="http://www.open-std.org/mailman/listinfo/unicode"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://www.open-std.org/mailman/listinfo/unicode</a><br>
> <br>
> <br>
_______________________________________________<br>
SG16 Unicode mailing list<br>
<a href="mailto:Unicode@isocpp.open-std.org" target="_blank"
moz-do-not-send="true">Unicode@isocpp.open-std.org</a><br>
<a href="http://www.open-std.org/mailman/listinfo/unicode"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://www.open-std.org/mailman/listinfo/unicode</a><br>
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<pre class="moz-quote-pre" wrap="">_______________________________________________
SG16 Unicode mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Unicode@isocpp.open-std.org">Unicode@isocpp.open-std.org</a>
<a class="moz-txt-link-freetext" href="http://www.open-std.org/mailman/listinfo/unicode">http://www.open-std.org/mailman/listinfo/unicode</a>
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