When using the name of a template variable or concept in places
where an expression was expected, Clang would drop the cxxscope token
preceeding it, if any.
This leads to subpar diagnostics - complaining about the
identifier being undeclared as clang would not know to look into a
We make sure the scope is preserved.
When encountering ns::Concept foo x;, Clang would also fail
to provide the same quality as it does at global scope.