[Bug fortran/85357] gfortran versions 7.2.0/8.0.1 reject F03 procedure overriding

[janus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85357

--- Comment #6 from janus at gcc dot gnu.org ---
(In reply to cfd from comment #5)
> It would be rather surprising if the Fortran standard viewed this as being
> invalid code (the procedure in question is bound to a dervied type, 
> hence should
> be overridable).

Note that the error has nothing to do with type binding or overriding at all.
It concerns the name clash of the two subroutines. This reduced version
(without any derived types) shows the same error (and ICE):

module base

   implicit none

contains

   subroutine summation(i,j)
      integer(4), intent(in) :: i
      integer(4), intent(out) :: j
      j = i + 1
   end subroutine

end module base


module extended

   use base
   implicit none

contains

   subroutine summation(i,j)
      integer(4), intent(in) :: i
      integer(4), intent(out) :: j
      j = i + 2
   end subroutine

end module extended


You have plenty of options to get around the error:
a) Don't use-import the first 'summation' routine in the second module (as
shown comment 1).
b) Make the 'summation' routines private and only make them available via the
type binding.
c) Use two different names, e.g.


   type, abstract :: base_type
   contains
      procedure :: summation => summation_base
   end type base_type

   type, extends(base_type) :: extended_type
   contains
      procedure :: summation => summation__ext
   end type extended_type