[Bug fortran/106856] [12/13 Regression][OOP] CLASS attribute handling / ICE in gfc_conv_expr_present, at fortran/trans-expr.cc:1977 since r12-4346-geb92cd57a1ebe7cd

["anlauf at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106856

anlauf at gcc dot gnu.org changed:

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

--- Comment #3 from anlauf at gcc dot gnu.org ---
Created attachment 54030
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54030&action=edit
Incremental patch

The above patch on top of Tobias' initial one fixes some minor issues with
it and improves the behavior for testcase class_75.f90 modified as follows:

! { dg-do compile }
! { dg-additional-options "-fcoarray=single" }
!
! PR fortran/106856
!
!
!
subroutine foo(x,y)
  class(*), optional :: x, y
  optional    :: x    ! { dg-error "Duplicate OPTIONAL attribute" }
  target      :: x
  allocatable :: x
  target      :: x    ! { dg-error "Duplicate TARGET attribute" }
  allocatable :: x    ! { dg-error "Duplicate ALLOCATABLE attribute" }
  pointer     :: y
  contiguous  :: y
  pointer     :: y    ! { dg-error "Duplicate POINTER attribute" }
  contiguous  :: y    ! { dg-error "Duplicate CONTIGUOUS attribute" }
  dimension   :: x(:,:)
  dimension   :: y(:,:,:)
  codimension :: x[:]
    ! < duplicat error for dimension/codimension: TODO add decl.

  ! Currently gives an ICE :-(
end


Note that these patches "regress" as follows:

- gfortran.dg/interface_41.f90 - this had a bogus error on valid code!
  (Removing the dg-error fixes it.)

- gfortran.dg/pr69398.f90 - this ICEs due to the duplicate DIMENSION attribute

I tried to modify restore_old_symbol() to handle CLASS arrays, but then
we ICE along a different path.  Not sure if this is the right approach.

Nevertheless, the patch as is already appears to be a great step forward!