[Bug c++/77912] New: class template deduction fails in template functions and generic lambdas

[jeff.mirwaisi at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77912

            Bug ID: 77912
           Summary: class template deduction fails in template functions
                    and generic lambdas
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jeff.mirwaisi at gmail dot com
  Target Milestone: ---

//deduction for the template type parameter of the simple class template below 
//fails when used in a generic context
template<class T> struct S{S(T){}}; 

//error: invalid use of template type parameter 'S'
template<class T> auto f(T t){return S(t);}

int main()
{
  //fails
  f(42);

  //fails
  //error: invalid use of template type parameter 'S'
  [](auto a){return S(a);}(42); 

  //works
  [](int a){return S(a);}(42);
}