[Bug fortran/64958] Warn if INTENT(IN) is changed by passing to no-intent argument

[mark.eggleston at codethink dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64958

--- Comment #5 from MarkEggleston <mark.eggleston at codethink dot com> ---
Warning is output by gfortran 6.3.0.

program test
  implicit none
  integer :: b
  integer :: c

  b = 0
  c = 7

  call sub(b)
  call sub(c)
  write(*,*) b, c

contains
  subroutine sub(x)
    integer, intent(in) :: x
    integer :: y
    x = 9
    y = x
  end subroutine sub
end program test

results in:

     x = 9
    1
Error: Dummy argument ‘x’ with INTENT(IN) in variable definition context
(assignment) at (1)

Warning also given by 7.4, 8.3, 9.1 and trunk.