CWG3077 [cpp.pre] Forming `import _string-literal_` directives not desirable

[hubert-reinterpretcast]

Full name of submitter (unless configured in github; will be published with the issue): Hubert Tong

Reference (section label): [cpp.pre]

Link to reflector thread (if any): N/A

Issue description:

https://wg21.link/cpp.pre#1.2 triggers import directive recognition for

#define STR(X) #X
const char *str = STR(
import u8"hello";
);

Such an import directive invariably leads to IFNDR (see #768). The stated goal of https://wg21.link/p1857 is to "[fine-tune] the context-sensitivity of import [ ... ]". The string-literal provision for triggering import directive recognition at the start of phase 4 is not consistent with such an intent: since header-name‌s are directly formed in this context, the only string-literal‌s seen will lead to IFNDR.

Suggested resolution:

Strike in https://wg21.link/cpp.pre#1.2:

• an import preprocessing token immediately followed on the same logical source line by a header-name, <, identifier, string-literal, or : preprocessing token, or

[hubert-reinterpretcast]

@jensmaurer, I would like to discuss this on Friday.

[jensmaurer]

CWG3077

[hubert-reinterpretcast]

CWG3077

Thanks Jens! There's a minor typo in the write-up:
reamin => remain

[jensmaurer]

Fixed typo.