IFNDR is definitely too far. I think even weak library UB is too far. The
function behaves perfectly deterministically even though it's not the
desired result. Mojibake is not UB. That we've improved the descriptive
language so we can discuss "literal encoding" hasn't changed the behavior
of anything.

`sprintf` has had this behavior forever.

Since the format is user extensible, I don't think any assumptions can be
made about the result of print, or format, being well formed for any
encoding that has well formed conditions. For the UTF-8 to UTF-16 case,
print has to do _something_, so it might as well try to do something
sensible. In most cases, though, it should be doing nothing.

On Wed, May 26, 2021 at 11:05 PM Hubert Tong via SG16 <sg16_at_[hidden]>
wrote:

> On Wed, May 26, 2021 at 5:46 PM Corentin Jabot via SG16 <
> sg16_at_[hidden]> wrote:
>
>>
>>
>> On Wed, May 26, 2021 at 11:01 PM Peter Brett via SG16 <
>> sg16_at_[hidden]> wrote:
>>
>>> Hi all,
>>>
>>> I prepared these 2 polls for tonight's meeting, but we did not have the
>>> opportunity to vote on them. I hope we will be able to vote on them next
>>> time. Please suggest alternative or additional polls that you think would
>>> be informative!
>>>
>>> Peter
>>>
>>>
>>> If, and only if, the literal encoding is UTF-8, <print> facilities
>>> should assume
>>> that their formatted results are UTF-8 text.
>>>
>>> SF F N A SA
>>>
>>> Attendance:
>>>
>>> Consensus:
>>>
>>> Author's position:
>>>
>>>
>>> If a <print> facility assumes that the result of formatting is UTF-8
>>> text, but
>>> it is not, then the program is ill-formed, no diagnostic required.
>>>
>>
>> Please make it UB
>>
>
> +1
>
>
>> IFNDR is really nasty and should be reserved for things that the compiler
>> has no real control over like ODR issues.
>>
>
> IFNDR can only be applied based on the source code. IFNDR cannot be
> applied depending on user input at run-time.
>
>
>>
>> Library has wording stating that preconditions violations are UB
>> http://eel.is/c++draft/library#structure.specifications-3.3
>> I think having wording along the line of "Precondition: The format string
>> is UTF-8 encoded" in the wording of vprint_unicode is the best way to
>> achieve this intent.
>>
>
> The above won't cover strings provided by the user for replacements (and
> that's probably just the easiest case to identify).
>
>
>>
>>
>>>
>>> SF F N A SA
>>>
>>> Attendance:
>>>
>>> Consensus:
>>>
>>> Author's position:
>>>
>>> --
>>> 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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>