[Bug c++/107773] New: Class members do not hide nested types

["eiband at mail dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107773

            Bug ID: 107773
           Summary: Class members do not hide nested types
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eiband at mail dot de
  Target Milestone: ---

The following program exits with code 1.

test.cpp:

struct a
{
  using get = void;
};

struct b : a
{
  int get(int i) const;
};

template <typename T>
concept c = requires { typename T::get; };

int main()
{
  return c<b>;
}

$ g++ test.cpp -std=c++20
$ ./a.out
$ echo $?
1

Expected is exit code 0, because T::get is not a type for T=b.

The code snippet is based on user "apple apple"'s comment on
https://stackoverflow.com/questions/74509418/why-does-member-function-not-hide-type-alias-in-base-class-when-compiling-with-g.

User "n. m." also notes that GCC happily compiles
https://eel.is/c++draft/temp.res.general#example-4 which does not use concepts
and should emit an error.

$ g++ -v
gcc version 11.1.0 (Ubuntu 11.1.0-1ubuntu1~20.04)