[Bug fortran/109345] New: class(*) variable that is a string array is not handled correctly

[Bug fortran/109345] New: class(*) variable that is a string array is not handled correctly

[lchilutti at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109345

            Bug ID: 109345
           Summary: class(*) variable that is a string array is not
                    handled correctly
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lchilutti at gmail dot com
  Target Milestone: ---

program test
implicit none
character(len=255)     :: str_array(2)   !< Array of strings

str_array(1) = ""
str_array(2) = ""

str_array(1) = "2880:2880,1:2160::1:1,1:2160"
str_array(2) = "1:1440,2160:2160::2880:1441,2160:2160"

call foo(str_array) !< class(*)
call foo2(str_array) !< char type
call foo3(str_array) !< class(*) with str copy

contains

subroutine foo ( var) !< Uses class(*)
class(*), intent(in) :: var(:)
integer :: i

select type (var)
type is (character(len=*))
  print *, "Using class(*)"
  print *, "The size of var:", size(var)
  do i = 1, size(var)
    print *, len_trim(var(i)), "data:", trim(var(i))
  enddo
end select
end subroutine

subroutine foo2 (var) !< Uses char type
character(len=*), intent(in) :: var(:)
integer :: i
  print *, "Not using class(*)"
  print *, "The size of var:", size(var)
  do i = 1, size(var)
    print *, len_trim(var(i)), "data:", trim(var(i))
  enddo
end subroutine

subroutine foo3 (var) !< Uses class(*) with a workaround
class(*), intent(in) :: var(:)
integer :: i
character(len=:), dimension(:), allocatable :: str

select type (var)
type is (character(len=*))
  str = var !< if you copy the class(*) var to an allocatable string it works
  print *, "Using class(*), with string copy workaround"
  print *, "The size of str:", size(str)
  do i = 1, size(str)
    print *, len_trim(str(i)), "data:", trim(str(i))
  enddo
end select
end subroutine
end program

If I compile the above program with gfortran (gcc version 12.2.0), I get the
following output:

Using class(*)
 The size of var:           2
          28 data:2880:2880,1:2160::1:1,1:2160
         255 data:880:2880,1:2160::1:1,1:2160                                  
                                                                               
                                                                               
                                1
 Not using class(*)
 The size of var:           2
          28 data:2880:2880,1:2160::1:1,1:2160
          37 data:1:1440,2160:2160::2880:1441,2160:2160
 Using class(*), with string copy workaround
 The size of str:           2
          28 data:2880:2880,1:2160::1:1,1:2160
          37 data:1:1440,2160:2160::2880:1441,2160:2160

You can see that when we give an array of strings as an argument to a function
using class(*) and select type, the string returned within the select type
function is incorrect.  We found a workaround in which we can copy the class(*)
input variable to an allocatable string within the select type statement, but
we should not have to do this.