According to [dcl.type.elab] p4:
> If an _elaborated-type-specifier_ appears with the `friend` specifier
as an entire _member-declaration_, the _member-declaration_ shall have
one of the following forms:
> `friend` _class-key_ _nested-name-specifier_(opt) _identifier_ `;`
> `friend` _class-key_ _simple-template-id_ `;`
> `friend` _class-key_ _nested-name-specifier_ `template`(opt)
_simple-template-id_ `;`
Notably absent from this list is the `enum` form of an
_elaborated-type-specifier_ "`enum` _nested-name-specifier_(opt)
_identifier_", which appears to be intentional per the resolution of
CWG2363.
Most major implementations accept these declarations, so the diagnostic
is a pedantic warning across all C++ versions.
In addition to the trivial cases previously diagnosed in C++98, we now
diagnose cases where the _elaborated-type-specifier_ has a dependent
_nested-name-specifier_:
```
template<typename T>
struct A
{
enum class E;
};
struct B
{
template<typename T>
friend enum A<T>::E; // pedantic warning: elaborated enumeration type cannot be a friend
};
template<typename T>
struct C
{
friend enum T::E; // pedantic warning: elaborated enumeration type cannot be a friend
};
```
This reverts commit f2583f3acf596cc545c8c0e3cb28e712f4ebf21b.
There is a large body of non-conforming C-like code using format strings
like this:
#define PRIuS "zu"
void h(size_t foo, size_t bar) {
printf("foo is %"PRIuS", bar is %"PRIuS, foo, bar);
}
Rejecting this code would be very disruptive. We could decide to do
that, but it's sufficiently disruptive that I think it requires
gathering more community consensus with an RFC, and Aaron indicated [1]
it's OK to revert for now so continuous testing systems can see past
this issue while we decide what to do.
[1] https://reviews.llvm.org/D153156#4607717
During the ISO C++ Committee meeting plenary session the C++23 Standard
has been voted as technical complete.
This updates the reference to c++2b to c++23 and updates the __cplusplus
macro.
Drive-by fixes c++1z -> c++17 and c++2a -> c++20 when seen.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D149553
