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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/102641] Bogus error for intent(out) dummy that is a
 polymorphic assumed-rank array
Date: Thu, 07 Oct 2021 16:08:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102641

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |burnus at gcc dot gnu.org

--- Comment #1 from Tobias Burnus <burnus at gcc dot gnu.org> ---
The issue with the code in comment 0 is that GCC has in resolve.c's
resolve_symbol:

  if (sym->ts.type =3D=3D BT_DERIVED
      ....
      if ((!a->save && !a->dummy && !a->pointer
          ...
        apply_default_init (sym);

and likewise a few lines below for BT_CLASS.

As there is now code which references the dummy variable, the error
  Assumed-rank variable y at (1) may only be used as actual argument
is shown.

 * * *

And in a similar vain, the following produces an ICE. It is quite similar
but as it uses an allocatable component, the code is generated after
resolving the symbols - such that an ICE and not a bogus error is the
result:

module m
  implicit none (type, external)
  type t
    integer, allocatable :: x
  end type t
contains
  subroutine foo(x)
    type(t), intent(out) :: x(..)
  end
end


Note: C839 (=E2=86=92 PR 54753) prevents some odd corner cases (involving a=
ssumed size
arrays).

One way to handle it would be to handle it in the caller and not in the cal=
lee.
However, this still requires support for assumed-rank as the following shou=
ld
be valid:

  subroutine foo(x)
    type(t), intent(out) :: x(..)
    ...
  subroutine bar(y)
    type(t), allocatable :: y(..)
    call foo(x)

(y has to be either allocatable or a pointer in order not to violate C839.)

As the issue with finalization, polymorphism, allocatable components and
default initialization cannot occur with BIND(C), there is no issue if foo =
or
bar is BIND(C).=