[Bug fortran/82064] New: [OOP] multiple incompatible definitions of extended derived type via module use

["daanvanvugt at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82064

            Bug ID: 82064
           Summary: [OOP] multiple incompatible definitions of extended
                    derived type via module use
           Product: gcc
           Version: 7.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: daanvanvugt at gmail dot com
  Target Milestone: ---

Created attachment 42097
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42097&action=edit
Makefile, base type, extra module and test program

When using an extended derived type from a module through two, different, other
modules they become incompatible.
The interesting part is that I use `private` everywhere so the type itself is
not actually shared.

This results in interesting phenomena such as select type not working as
expected, and errors of class(t1) not matching class(t1).

In the attached zip file are the files needed to reproduce.
Run `make` to create `test_sep` from test_sep.f90 which prints ERR twice on my
machine.
Putting all the modules and the program together in one file yields a program
that prints OK twice. (test.f90)

I have written some changes that cause the problem to disappear as comments.



module mod_types
  type, abstract :: t
  end type t
  type, extends(t) :: t2
  end type t2
end module mod_types

module mod_f
  use mod_types
  implicit none
  private
contains
! Remove this function to fix
subroutine f(particle)
  ! if the classname here matches the type name in test_sep it breaks
  class(t2), intent(inout) :: particle
  ! using type instead of class here also works
end subroutine f
end module mod_f

module mod_test
  use mod_types
  !use mod_boris ! uncomment for a fix
  implicit none
  private
  public :: init
contains

subroutine init(p)
  class(t), intent(inout) :: p
  select type (p)
  type is (t2)
    write(*,*) "OK"
  class default
    write(*,*) "ERR"
  end select
end subroutine init
end module mod_test




program test_sep
use mod_types
use mod_f ! remove this to fix
use mod_test

class(t), allocatable :: p
type(t2) :: p2
allocate(t2::p)
call init(p)
call init(p2)
end program test_sep