Mangling for unnamed enumerations with an enumerator name for linkage purposes (P2115)

[wreien]

P2115R0 gave unnamed enumerations that don't already have a typedef name for linkage purposes the name of their first enumerator for linkage purposes. From https://eel.is/c++draft/dcl.enum#12:

An unnamed enumeration that does not have a typedef name for linkage purposes ([dcl.typedef]) and that has a first enumerator is denoted, for linkage purposes ([basic.link]), by its underlying type and its first enumerator; such an enumeration is said to have an enumerator as a name for linkage purposes.

To mangle both the underlying type and the name of an enum requires a new production. To be able to continue to differentiate an unnamed enum, I propose something like the following (in a similar manner to closure type productions):

<unnamed-type-name> ::= <unnamed-enum-name>

<unnamed-enum-name> ::= Ue <underlying type> <enumerator source-name>

So, for instance, the types of the following enums would be mangled as follows:

enum { A };  // Uej1A, assuming underlying type is unsigned int
enum : long long { foo, bar };  // Uex3foo