gcc/testsuite/gfortran.dg/interface_40.f90

! { dg-do compile }
! PR fortran/78814
! Code contributed by Gerhard Steinmetz
program p
   class(*) :: x  ! { dg-error " must be dummy, allocatable or pointer" }
   print *, f(x) ! { dg-error "Explicit interface required" }
end