On Wed, May 12, 2021 at 3:14 PM Victor Zverovich <victor.zverovich_at_[hidden]>
wrote:

> Hi Hubert,
>
> Thanks for the suggestions, I'll try incorporating them in the next
> iteration of the paper.
>
> > I think it would help if the point was stated more explicitly ...
>
> Good idea, will clarify this.
>
> > The paper can at least acknowledge that "polyglot" string literals
> exist ...
>
> Sure.
>
> > we'll end up with cases where the literal encoding is UTF-8 but the user
> won't want the UTF-8 std::print behaviour to potentially kick in.
>
> I am a bit skeptical because I haven't seen any reports about cases like
> this from the extensive usage experience of this feature. We can't fix
> clearly broken things and be bug-to-bug compatible with legacy APIs at the
> same time.
>
> > At least two cases come to mind.
>
> I don't think we can do much if users decide to lie about the encoding. We
> should make the common case work rather than try making everyone happy and
> support theoretical use cases not backed by actual implementation and usage
> experience.
>

I'm concerned that deployment experience might be limited to specific
environments. I expect the conditions for the second scenario are met very
easily on *nix and also very difficult to test for (requires some sort of
special test environment/harness).


> That said they can always use nonunicode function or continue using their
> legacy APIs in those cases.
>

I think the non-Unicode function is awkwardly named.


>
> Cheers,
> Victor
>
>
>
>
> On Tue, May 11, 2021 at 8:23 PM Hubert Tong <
> hubert.reinterpretcast_at_[hidden]> wrote:
>
>> On Tue, May 11, 2021 at 8:41 PM Victor Zverovich via SG16 <
>> sg16_at_[hidden]> wrote:
>>
>>> Dear Unicoders,
>>>
>>> Here is a link to a new revision of P2093:
>>> https://isocpp.org/files/papers/D2093R6.html. It's essentially the same
>>> as R5 but addresses the latest LEWG feedback and adds a few clarifications.
>>> The only change to the wording is replacing <io> with <print>.
>>>
>>
>> Thanks Victor.
>>
>> With respect to the choice to transcoding, it took me a while to catch on
>> to the statement being made. I think it would help if the point was stated
>> more explicitly that the choice to perform replacement during transcoding
>> is because that is consistent with the treatment of malformed UTF-8 for
>> UTF-8-native terminals and the choice not to transcode in the case where
>> the terminal is UTF-8 native is because we expect the terminal to behave
>> predictably as-is we did do the "transcoding".
>>
>> I'm still not entirely convinced about the argument surrounding the
>> choice of using the literal encoding though. The paper can at least
>> acknowledge that "polyglot" string literals exist and partially obviates
>> the insistence that the literal encoding being UTF-8 according to the build
>> system/build mode means that the involvement of non-UTF-8 strings in the
>> vicinity of std::print constitutes "mixing encodings".
>>
>> I really think that, just for predictability surrounding the display of
>> substitution text, we'll end up with cases where the literal encoding is
>> UTF-8 but the user won't want the UTF-8 std::print behaviour to potentially
>> kick in.
>>
>> At least two cases come to mind:
>> (1) Printing using both legacy interfaces and std::print where the legacy
>> interfaces are not using UTF-8 may appear fine on some terminals but would
>> result, on redirect, in output with mixed encoding.
>>
>> (2) std::print where the literal encoding is UTF-8 but the literals are
>> all "polyglot" and substitution strings that are not UTF-8 can appear to be
>> okay when redirecting or printing to non-Unicode terminals; however, once
>> deployed to a Unicode terminal, replacement characters show up (even if the
>> output is properly encoded for the underlying C output interface).
>>
>>
>>>
>>> Cheers,
>>> Victor
>>>
>>> On Tue, May 11, 2021 at 11:02 AM Tom Honermann via SG16 <
>>> sg16_at_[hidden]> wrote:
>>>
>>>> Reminder that this meeting is taking place tomorrow.
>>>>
>>>> Per suggestion by Peter, the agenda order is being changed to review
>>>> the updates in P2295R2 before D2372R1 and P2093R5 in the hopes that we can
>>>> forward P2295R2 to EWG. We'll try to limit that discussion to 30 minutes.
>>>> The updated agenda is below. Again, we are unlikely to get to P2348R0 at
>>>> all.
>>>>
>>>> - P2295R2: Support for UTF-8 as a portable source file encoding
>>>> <https://wg21.link/p2295r3>
>>>> - Review updates intended to address prior SG16 feedback.
>>>> - D2372R1: Fixing locale handling in chrono formatters
>>>> <https://isocpp.org/files/papers/D2372R1.html>
>>>> - Affirm or rebut LEWGs position.
>>>> - P2093R5: Formatted output <https://wg21.link/p2093r5>
>>>> - Discuss locale dependent character encoding concerns.
>>>> - P2348R0: Whitespaces Wording Revamp <https://wg21.link/p2348r0>
>>>>
>>>> Tom.
>>>>
>>>> On 5/4/21 12:06 AM, Tom Honermann via SG16 wrote:
>>>>
>>>> SG16 will hold a telecon on Wednesday, May 12th at 19:30 UTC (timezone
>>>> conversion
>>>> <https://www.timeanddate.com/worldclock/converter.html?iso=20210512T193000&p1=1440&p2=tz_pdt&p3=tz_mdt&p4=tz_cdt&p5=tz_edt&p6=tz_cest>
>>>> ).
>>>>
>>>> The agenda is:
>>>>
>>>> - D2372R1: Fixing locale handling in chrono formatters
>>>> <https://isocpp.org/files/papers/D2372R1.html>
>>>> - Affirm or rebut LEWGs position.
>>>> - P2093R5: Formatted output <https://wg21.link/p2093r5>
>>>> - Discuss locale dependent character encoding concerns.
>>>> - P2295R2: Support for UTF-8 as a portable source file encoding
>>>> <https://wg21.link/p2295r3>
>>>> - Review updates intended to address prior SG16 feedback.
>>>> - P2348R0: Whitespaces Wording Revamp <https://wg21.link/p2348r0>
>>>>
>>>> Our last telecon was consumed by discussion
>>>> <https://github.com/sg16-unicode/sg16-meetings/blob/master/README.md#april-28th-2021>
>>>> of LWG3547 <https://cplusplus.github.io/LWG/issue3547> and possible
>>>> remedies. Though we did not reach consensus on a direction forward during
>>>> that telecon, Victor and Corentin, at the LEWG chair's request, drafted
>>>> D2372R0, presented it at the LEWG telecon held 2021-05-03
>>>> <https://wiki.edg.com/bin/view/Wg21telecons2021/P2372#2021-05-03>, and
>>>> LEWG reached strong consensus for it. The D2372R0 revision will be
>>>> submitted for the May mailing as P2372R0; and a D2372R1
>>>> <https://isocpp.org/files/papers/D2372R1.html> revision addressing
>>>> LEWG feedback will be submitted as P2372R1. Both revisions substantially
>>>> match the proposed resolution that SG16 discussed. Since SG16 did not
>>>> reach consensus on that direction, the LEWG chair has asked that we revisit
>>>> it to either affirm or rebut the LEWG consensus. We will therefore
>>>> (briefly) discuss and then poll that direction. Note that the poll taken
>>>> in SG16 differs from the poll taken in LEWG. In SG16, we polled applying
>>>> the proposed resolution to C++23 while LEWG polled applying the proposed
>>>> resolution (with amendments to not change behavior for iostream
>>>> manipulators) to C++23 *and* retroactively to C++20.
>>>>
>>>> Once we've dispatched D2372R1, we'll return to the original agenda for
>>>> our last telecon; discussion of P2093R5 <https://wg21.link/p2093r5>
>>>> (Formatted output) and P2295R2 <https://wg21.link/p2295r3> (Support
>>>> for UTF-8 as a portable source file encoding). I've retained P2348R0
>>>> <https://wg21.link/p2348r0> on the agenda, though I don't expect that
>>>> we'll get to it.
>>>>
>>>> With regard to P2093R5 <https://wg21.link/p2093r5>, the current status
>>>> is that LEWG has referred the paper back to SG16 for further discussion;
>>>> please see the LEWG meeting minutes here
>>>> <https://wiki.edg.com/bin/view/Wg21telecons2021/P2093#Library-Evolution-2021-04-06>.
>>>> Specifically, LEWG would benefit from additional analysis of previously
>>>> deferred questions <http://lists.isocpp.org/lib-ext/2021/03/18189.php>
>>>> regarding character encoding concerns, transcoding requirements (or the
>>>> lack there of) and the ensuing consequences (or lack there of).
>>>>
>>>> 1. How errors in transcoding should be handled. E.g., when
>>>> transcoding from UTF-8 to a UTF-16 based console interface and the UTF-8
>>>> input is not well-formed.
>>>> 2. The choice to base behavior on the compile-time choice of
>>>> literal encoding. An implication of the current proposal is that a program
>>>> that contains only ASCII characters in string literals will change behavior
>>>> depending on whether the literal encoding is UTF-8 vs ASCII (or some other
>>>> ASCII derived encoding).
>>>> 3. Whether transcoding to the console interface encoding should be
>>>> performed when the literal encoding is not UTF-8.
>>>> 4. What the implications are for future support of std::print("{}
>>>> {} {} {}", L"Wide text", u8"UTF-8 text", u"UTF-16 text", U"UTF-32
>>>> text").
>>>>
>>>> I think these concerns will be easier to resolve if we first reach
>>>> consensus regarding scenarios in which localized text may be provided in an
>>>> unexpected encoding. The following is a slightly modified example of code
>>>> Hubert previously provided. The example has been modified to explicitly
>>>> opt into localized chrono formatting.
>>>>
>>>> std::print("{:L%p}\n",
>>>> std::chrono::system_clock::now().time_since_epoch());
>>>>
>>>> At issue is the encoding used by locale sensitive chrono formatters.
>>>> The example above contains the %p specifier and is locale sensitive
>>>> because AM/PM designations may be localized. In a Chinese locale the
>>>> desired translation of "PM" is "下午", but the locale will provide the
>>>> translation in the locale encoding. As specified in P2093R5, if the
>>>> literal encoding is UTF-8, than std::print() will expect the
>>>> translation to be provided in UTF-8, but if the locale is not UTF-8-based
>>>> (e.g., Big5; perhaps Shift-JIS for the Japanese 午後 translation), then the
>>>> result is mojibake.
>>>>
>>>> I had previously suggested the following possible directions we can
>>>> investigate to resolve the encoding concerns.
>>>>
>>>> - Specialize std::locale facets
>>>> <https://en.cppreference.com/w/cpp/locale/locale> and related I/O
>>>> manipulators like std::put_time()
>>>> <https://en.cppreference.com/w/cpp/io/manip/put_time> for char8_t.
>>>> This would allow std::print() to, when the literal encoding is
>>>> UTF-8, opt-in to use of the UTF-8/char8_t facets and I/O
>>>> manipulators.
>>>> - When the literal encoding is UTF-8, stipulate that running the
>>>> program in a non-UTF-8 based locale is non-conforming. This would
>>>> effectively require MSVC programmers to, when building code with the
>>>> /utf-8 option, to also force selection of a UTF-8 code page via a
>>>> manifest
>>>> <https://docs.microsoft.com/en-us/windows/uwp/design/globalizing/use-utf8-code-page>
>>>> and require use of Windows 10 build 1903 or later.
>>>> - When the literal encoding is UTF-8, specify that non-UTF-8 based
>>>> locale dependent translations be implicitly transcoded (such transcoding
>>>> should never result in errors except perhaps for memory allocation
>>>> failures).
>>>> - Drop the special case handling for the literal encoding being
>>>> UTF-8 and specify that, when bypassing a stream to write directly to the
>>>> console, that the output be implicitly transcoded from the current locale
>>>> dependent encoding (whatever it is) to the console encoding (UTF-8).
>>>>
>>>> If we get through all of that, we'll review Corentin's updates in
>>>> P2295R2 <https://wg21.link/p2295r3> to address prior SG16 feedback.
>>>> Thank you to everyone that already provided additional feedback on the
>>>> mailing list!
>>>>
>>>> Tom.
>>>>
>>>>
>>>> --
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>>>> SG16_at_[hidden]
>>>> https://lists.isocpp.org/mailman/listinfo.cgi/sg16
>>>>
>>> --
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>>>
>>