[Bug d/96229] New: Invalid specialization accepted when also constrained in base template template parameter

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96229

            Bug ID: 96229
           Summary: Invalid specialization accepted when also constrained
                    in base template template parameter
           Product: gcc
           Version: 10.1.0
               URL: https://godbolt.org/z/W1zh9n
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: johelegp at gmail dot com
  Target Milestone: ---

See https://godbolt.org/z/W1zh9n.
```C++
template <class T> concept Int = requires { T{0}; };
template <template <Int> class T> struct X        { };
template <Int>   /* ^~~ */        struct Y : X<Y> { };
                                  struct Z        { };
void f() { Y<Z> x; }
```