This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116c. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-03-27
Subclause 16.4.5.3.3 [macro.names] paragraph 2 specifies a prohibition against keywords, alternative tokens, and attributes being used as macro names. There is no such protection for parameter names of #embed, but the use of embed-parameters should be protected there and in the __has_embed argument.
Arguably, 16.4.5.3.3 [macro.names] constrains only programs that use the standard library, because header files of the standard library must be able to rely on a sane environment; see also 16.4.5.3.1 [reserved.names.general]:
The C++ standard library reserves the following kinds of names: ...
Arguably, standard library headers can be crafted or auto-generated such that they do not make use of #embed, or at least not use #embed with parameters. In any case, this would be a concern of the standard library, not of the core language.
Possible resolution:
Change in 15.1 [cpp.pre] paragraph 3 as follows:
If one of the pp-tokens of a #embed directive (before macro replacement) is the identifier limit, prefix, suffix, or if_empty and that identifier is defined as a macro (15.7.1 [cpp.replace.general]), the program is ill-formed. Any embed-prefixed-parameter is conditionally-supported, with implementation-defined semantics.
Change in 15.2 [cpp.cond] paragraph 11 as follows:
Prior to evaluation, macro invocations in the list of preprocessing tokens that will become the controlling constant expression are replaced (except for those macro names modified by the defined unary operator), just as in normal text. If replacement of macros in the preprocessing tokens following the sequence __has_embed ( and before a matching ) (possibly produced by macro expansion) encounters a preprocessing token that is one of the identifiers limit, prefix, suffix, or if_empty and that identifier is defined as a macro (15.7.1 [cpp.replace.general]), the program is ill-formed. If the preprocessing token defined is generated as a result of this replacement process or use of the defined unary operator does not match one of the two specified forms prior to macro replacement, the behavior is undefined.