[Bug c++/103852] [10/11/12 Regression] Alias template argument deduction is available in C++17 mode

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103852

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |accepts-invalid
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
      Known to fail|                            |10.1.0
      Known to work|                            |9.1.0
   Last reconfirmed|                            |2021-12-28
   Target Milestone|---                         |10.4
            Summary|Alias template argument     |[10/11/12 Regression] Alias
                   |deduction is available in   |template argument deduction
                   |C++17 mode                  |is available in C++17 mode

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed reduced testcase:
template <class T> struct b{};
template <class T, class T1 = b<T>>
struct s
{
    s(T);
};
s c(100);
template <class T, class T1 = b<T>>
using ss = s<T, T1>;
ss tt(1);

---- CUT ----
tt defintion should fail in C++17 while pass in C++20.


It looks like when the support was added it was added unconditionally; could
there have been a Defect report?