[Bug fortran/64138] gfortran interface issue

[sgk at troutmask dot apl.washington.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64138

--- Comment #6 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Tue, Dec 02, 2014 at 03:37:19PM +0000, wong.david-c at epa dot gov wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64138
> 
>    What is your fix?
> 

I meant I fixed the code you posted.  It was missing a CONTAINS
statement before c_sub_cc, and there is an extra 'j' on the
end of one of the 'end function c_sub_??' lines.

>    In the original code, c_sub_cr and c_sub_rc are distinct because the
> sequence of argument type are different. Other compilers have no problem to
> distinguish them. Please advise.

You can get the code to compile if you change the dummy
argument names in c_sub_cr and c_sub_rc to unique entities.
For example, (and yes I changed the function and variable
names while debugging)

      type(complex_number) function f2(z1, num)
         type (complex_number), intent(in) :: z1
         real(kind=dp), intent(in) :: num
         f2%re = z1%re - num
         f2%im = z1%im
       end function f2

      type(complex_number) function f3(num, z2)
         type (complex_number), intent(in) :: z2
         real(kind=dp), intent(in) :: num
         f3%re = num - z2%re
         f3%im = - z2%im
      end function f3

The only problem with this workaround is that you cannot
use keyword argument association.  For example,

   type(complex_number) :: z=complex_number(1.,2.)
   real x = 3. 
   z = c_sub(num=x, z)

The above is ambiguous because the reduced argument list for
f2 and f3 are identical, so the generic c_sub can be mapped
to either.  Fortunately, gfortran tries to help in this 
situation

% gfortran -o z -fmax-errors=1 a.f90
a.f90:53.18:

  b = c_sub(num=x, a);    print '(A,2F5.1)', '(x-a)? = ', b%re, b%im
                  1
Error: Missing keyword name in actual argument list at (1)
Fatal Error: Error count reached limit of 1.

Note, however, AFAIK, a keyword is not necessary and is not required.
IHMO, issuing this error message could in fact be considered a bug.
In fact, if you change the order of arguments to

  b = c_sub(a, num=x);    print '(A,2F5.1)', '(x-a)? = ', b%re, b%im

This will compile without error.  If the former line producing an
error about a missing keyword shouldn't the latter?