[Bug c++/87910] New: Missing typename/template not diagnosed

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87910

            Bug ID: 87910
           Summary: Missing typename/template not diagnosed
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

While working on P0634 I noticed that the following testcase is accepted while
it probably shouldn't be:

template<typename T> struct A {
  template<typename U> struct B;
  template<typename U> using C = U;
};

template<typename T> A<T>::B<T> f1();
template<typename T> A<T>::C<T> f2();

The dependent names "A<T>::B<T>" should be prefixed by the typename keyword,
and the template keyword should come after ::.

With P0634 that typename will no longer be required[*] but I think it still
requires "::template".

[*] it is a decl-specifier of the decl-specifier-seq of a simple-declaration or
a function-definition in namespace scope