Bug 103054 - [f18] Gfortran accepts invalid and rejects valid co_reduce argument keyword name

[Damian Rouson]

In TS 18508, the second summy argument of co_reduce was named
"operator."  In the Fortran 2018 standard, the corresponding argument
has the name "operation."  GFortran accepts the non-standard keyword
argument name "operator" and rejects the standard name "operation."

% cat co_reduce.f90
  implicit none
  logical :: co_all= .true.
  call co_reduce(co_all, operator=both)
  call co_reduce(co_all, operation=both)
contains
  logical pure function both(lhs,rhs)
    logical, intent(in) :: lhs, rhs
    both = lhs .and. rhs
  end function
end

% gfortran -fcoarray=single co_reduce.f90
co_reduce.f90:4:40:

    4 |   call co_reduce(co_all, operation=both)
      |                                        1
Error: Cannot find keyword named 'operation' in call to 'co_reduce' at (1)
% gfortran --version
GNU Fortran (Homebrew GCC 11.2.0) 11.2.0