[PATCH, fortran] PR89782 READ/WRITE of a character array when it is a parameter

[Jerry DeLisle]

Hi all,

The front-end is not consistently checking for errors with character parameters 
as internal units. The reason is we never actually checked for this before. In 
some cases an error message is triggered from other unrelated causes or 
sometimes no error is given at all.

This is fixed by the attached patch that adds the check in gfc_resolve_dt. I had 
to place the check before the unit expression is resolved because somewhere in 
gfc_resolve_expr the attribute information does not trigger for at least one 
test case (lost?).

All cases I found are included in the test case.  Regression tested on 
x86_64-pc-linux-gnu.

OK for trunk?

Regards,

Jerry

2019-06-22  Jerry DeLisle  <jvdeli...@gcc.gnu.org>

        PR fortran/89782
        * io.c (gfc_resolve_dt): Check that internal units are not
        character PARAMETER.

        * gfortran.dg/io_constraints.f90: New test.


! { dg-do compile }
program pr89782
  character(len=*),parameter :: VALUES(*)=[character(len=10) :: 'NaN','NAN','nan','Inf','INF','inf','Infinity']
  character(len=*),parameter :: VALUE='NaN'
  real(4) :: var
  do i=1,size(VALUES)
    read(VALUES(i),*) float ! { dg-error "character PARAMETER" }
    write(VALUES(i),*)float ! { dg-error "character PARAMETER" }
  enddo
  read(var,*)float    ! { dg-error "INTEGER expression or a CHARACTER" }
  read(VALUE,*)float  ! { dg-error "character PARAMETER" }
  write(VALUE,*)float ! { dg-error "character PARAMETER" }
end program pr89782