Fortran interface allowing rank-1 arrays and scalars

Question

Background: GCC 10 removed support for calling subroutines with different typed arguments. My aim is to write an interface that respects both integer, dimension(:) and integer.

(Which means I can't use other options such as embedding the scalar in an array. I have to change the interface)

According to GCC docs:

It is possible to provide standard-conforming code which allows different types of arguments by using an explicit interface and TYPE(*).

and:

Note, however, that TYPE(*) only accepts scalar arguments, unless the DIMENSION is explicitly specified. As DIMENSION(*) only supports array (including array elements) but no scalars, it is not a full replacement for C_LOC. On the other hand, assumed-type assumed-rank dummy arguments (TYPE(*), DIMENSION(..)) allow for both scalars and arrays, but require special code on the callee side to handle the array descriptor.

In the interface below I have type(*), dimension(:) :: data. How can I change it according to the text I've emphasized above?

module z
    interface
        subroutine a(data)
            type(*), dimension(:) :: data
        end subroutine a
    end interface
contains
    subroutine b(data)
        integer :: data
        call a(data)
    end subroutine
    subroutine c(data)
        integer, dimension(:) :: data
        call a(data)
    end subroutine
end module

Godbolt playground

Answer 1

I am not aware of GCC 10 removing anything (what is your source for that?) but exactly for the reasons you mention, GCC also introduced the directive

!GCC$ attributes no_arg_check::A 

(see Procedure for any type of array in Fortran )

which was already used in other compilers that enables the procedure to be called with any arguments, scalars or arrays of any rank, mainly for routines that accept buffers of any type, particularly in MPI libraries.

The new DIMENSION(..) is not really suited for use within Fortran, it requires special code that understands the standard Fortran array descriptor and it is mainly expected that it will be written in C. However, according to the very page you linked https://gcc.gnu.org/onlinedocs/gfortran/Further-Interoperability-of-Fortran-with-C.html#Further-Interoperability-of-Fortran-with-C gfortran does not yet support the standard array descriptor.