[Bug fortran/99765] New: Explicit dimension size declaration of pointer array allowed

["nickpapior at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99765

            Bug ID: 99765
           Summary: Explicit dimension size declaration of pointer array
                    allowed
           Product: gcc
           Version: 4.8.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nickpapior at gmail dot com
  Target Milestone: ---

A mishandling of variable declarations

Consider this program:

program test
  real, dimension(10), pointer :: a(:) => null()

  print *, associated(a)
  allocate(a(2))
  print *, size(a)
  !print *, size(a(1)) ! obviously fails as a(1) is a scalar

end program test


It is ambiguous to determine the size of a. The programmer may think that after
allocation one has 2x10 elements a(1:2)(1:10) however what is happening is that
the dimension(10) attribute is completely ignored.

I can't find anywhere in the standard mentioning that this way of definition is
wrong, but I think it clearly shouldn't be allowed.

I.e. it is unclear whether the user wants a(1:2)(1:10) or a(1:10)(1:2), in any
case neither of the results are achieved.

I found this bug in 4.8.4 and also in 9.3.0, so I assume it exists in all in
between.

A few more cases that resemble this:

  real, dimension(10), allocatable :: a(:)

behaves exactly like with pointers. It is not well-defined and gets to the
a(1:2) case.

  real, dimension(10), allocatable :: a(10)

rightfully errors out on compilation with a somewhat unclear error message

    3 |   real, dimension(10) :: a(10)
      |                          1
Error: Symbol ‘a’ at (1) already has basic type of REAL