On Tue, May 5, 2020 at 3:17 PM Tom Honermann via SG16 <sg16@lists.isocpp.org> wrote:

Agreed for that example. But for the other example I provided, the resulting identifier (if lexed such that \u0300\u0327 produces a single preprocessor token) is in NFC since there is no precomposed character for a capital letter A with grave and cedilla.

According to the implementation provided by https://minaret.info/test/normalize.msp (and also GCC), the NFC form is \u00c0\u0327.

Do we believe that that example should be well-formed?

The rationale for not allowing stray combining characters is that they may semantically combine, in terms of a text application, with characters from the basic source character set in a way that disagrees with how C++ tokenization works. This is why the wording makes the program ill-formed when the \u0300 is encountered right after forming it as a preprocessor token.