On Mon, Feb 24, 2020, 17:08 Hubert Tong via SG16 <sg16_at_[hidden]>
wrote:

> - Was EWG informed that the proposal can be understood as introducing new
>> core language undefined behaviour for existing programs with identifiers in
>> NFC form where the concatenation is not in NFC form ([cpp.concat])? I note
>> that R1 of the paper was not clear on that point and R2 does not identify
>> it as a consideration.
>>
>> I don't recall discussing this in EWG, but I believe it was discussed at
>> some point and the conclusion was that an identifier not in NFC form
>> resulting from such concatenation was ill-formed. Can you elaborate as to
>> how the UB manifests?
>>
> The typical manifestation of the UB in cpp.concat that does not produce a
> diagnostic for the case in question is that the concatenation may instead
> leave the operand tokens behind. That is, the ill-formed result is not
> required to manifest.
>

Could we modify the wording so that identifiers not nfc after
pre-processing are ill-formed?

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