Although using-enum's grammar is 'using elaborated-enum-specifier',
the lookup for the enum is ordinary lookup (and not the tagged-type
lookup that normally occurs wth an tagged-type specifier). Thus (a)
we can find typedefs and (b) do not find enum tags hidden by a non-tag
name (the struct stat thing).
This reimplements that part of using-enum handling, to address DR2621,
where clang's behaviour does not match std intent (and other
compilers).
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D134283
In Parser::ParseUsingDeclaration(...) when we call ParseEnumSpecifier(...) it is
not calling SetTypeSpecError() on DS when it detects an error. That means that
DS is left set to TST_unspecified. When we then pass DS into
Sema::ActOnUsingEnumDeclaration(...) we hit an llvm_unreachable(...) since it
expects it to be one of three states TST_error, TST_enum or TST_typename.
This fixes https://github.com/llvm/llvm-project/issues/57347
Differential Revision: https://reviews.llvm.org/D132695
Nathan Sidwell