[J3] Matching only arguments that are C interoperable?

[Jeff Hammond]

type(*), dimension(..) matches everything, which means that the C code on the receiving end of this will get things that it cannot process.  This forces libraries like MPI to error at runtime, which is not ideal.

Is there a way to filter out non-C-interoperable types?  For example, if I had a way to write an interface that matches only scalars and arrays of built-in types, and an interface that matches only C interoperable structs, then the other cases will fail to compile or link.

As best I can tell, I write specific interfaces with 16 dimensions (scalar+15D) times 15 (?) built-in types but that still leaves out C interoperable structs.  It also fails miserably in contexts where there is more than one buffer argument, as noted in https://www.researchgate.net/profile/Jeffrey-Squyres/publication/221596873_A_Case_for_New_MPI_Fortran_Bindings/links/00b7d536bbaff31de5000000/A-Case-for-New-MPI-Fortran-Bindings.pdf.

Am I missing something or is there no way to resolve whether I have C interoperable arguments at compile-time?

Thanks,

Jeff

PS if it helps to think about this with code, the following compiles without error, which someone else thought was correct.

module m

    type :: t
        integer :: i
        double precision :: d
        integer :: j(10)
        real :: r(100)
        real, allocatable :: z(:)
    end type t

    interface
        subroutine foo(t) bind(C)
            implicit none
            type(*), dimension(..) :: t
        end subroutine foo
    end interface

end module m

program main
    use m
    implicit none
    type(t) :: x
    call foo(x)
end program main