[cfe-dev] Advice on patch

[Nathan Sidwell via cfe-dev]

hi,  I've been working on p1099 
(http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1099r5.html)-- 
c++20's using-enum feature.  Among other things it allows you to being 
the enumerators of a scoped enumeration into the local scope 'using enum 
maybe-qualified-tag-name ;'  Brings the members of that enum in, as if 
by individual using declarations.  I posted an initial patch seeking 
advice on a couple of issues as https://reviews.llvm.org/D101370

I chose to extend EnumDecl, rather than a new decl as we still need the 
shadow decl chain.  The enum is parsed with ParseEnumSpecifier.

Q1)  I need to add the EnumDecl to the UsingDecl, and don't need the 
QualifiedLoc or DNLoc fields.  Should I use a local union to overlay 
those pieces of data, or just live with the size expansion?

Q2) When the scoped enum is a template member, the members are 
instantiated when one looks inside the enum -- not when the enum decl is 
instantiated.  That's done with RequireCompleteDeclContext, which is 
designed for when the parser is looking, and therefore takes a ScopeRef. 
  This is a new situation where we don't have a ScopeRef, we have an 
EnumDecl, which we desire to complete.  Is it best to break 
RequireCompleteDeclContext apart in some way so there's a new entry 
point for the new use?

thanks,

nathan

-- 
Nathan Sidwell