[Bug c++/99141] New: Name of deduced type unchecked in deduction guide

[Bug c++/99141] New: Name of deduced type unchecked in deduction guide

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99141

            Bug ID: 99141
           Summary: Name of deduced type unchecked in deduction guide
           Product: gcc
           Version: 11.0
               URL: https://godbolt.org/z/bEhjsc
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: johelegp at gmail dot com
                CC: johelegp at gmail dot com
  Target Milestone: ---

Context
(https://timsong-cpp.github.io/cppwp/n4861/temp.deduct.guide#nt:deduction-guide):
> deduction-guide:
>	explicit-specifieropt template-name ( parameter-declaration-clause ) -> simple-template-id ;
The requirement
(https://timsong-cpp.github.io/cppwp/n4861/temp.deduct.guide#3.sentence-3):
> The template-name shall be the same identifier as the template-name of the simple-template-id.
See https://godbolt.org/z/bEhjsc.
```C++
template<class>struct A;
template<class>using B=A<int>;
A(int)->B<int>;
```

[Bug c++/99141] Name of deduced type unchecked in deduction guide

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99141

Johel Ernesto Guerrero Peña <johelegp at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |11.0, 12.0

--- Comment #1 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Simpler: https://godbolt.org/z/EE9an4Whf.
```C++
template<class T>struct A{A(T){}};
using B=A<int>;
A(int)->B;
A a{0};
```

[Bug c++/99141] Name of deduced type unchecked in deduction guide

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99141

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-08-29

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug c++/99141] Name of deduced type unchecked in deduction guide

[liarokapis.v at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99141

Alexandros Liarokapis <liarokapis.v at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |liarokapis.v at gmail dot com

--- Comment #3 from Alexandros Liarokapis <liarokapis.v at gmail dot com> ---
This also affects namespaced-identifiers:

```C++
namespace foo {
    template <class T>
    struct bar { template <class X> bar(X); };

    template <class X>
    bar(X) -> foo::bar<int>;
}
```

The above shouldn't compile since the trailing return entity must be a
`simple-template-id`. Passes on every version of GCC so far.