The name of the module procedure conflicts with a name in the encompassing scoping unit

Question

I'm learning Fortran submodule, this is my code

module name1
    implicit none
    interface
        module subroutine test2(x)
            integer,intent(in) :: x
        end subroutine test2
    end interface
    contains
        subroutine test1(x)
            integer :: x
            call test2(x)
        end
end module name1


module name2
    use name1
    implicit none
    integer :: z = 22
end module name2


submodule(name1) new
    use name2
    contains
        subroutine test2(x)
            integer,intent(in):: x
            integer:: y 
            y = 2
            print *, x+y+z ,'from test2'
        end  
end submodule



program name
    use name2
    implicit none
    call test1(5)
end program name

But while compiling with ifort (IFORT) 2021.3.0 20210609 it shows the following error

test.f90(26): error #6645: The name of the module procedure conflicts with a name in the encompassing scoping unit.   [TEST2]
        subroutine test2(x)
-------------------^
compilation aborted for test.f90 (code 1)

I can't understand what I'm doing wrong. Is it not a valid Fortran submodule use?

Answer 1

When defining the implementation of a procedure in a submodule (a separate module procedure), you need the keyword module.

The relevant bits of your code would become:

module name1
  implicit none
  interface
    module subroutine test2(x)
      integer,intent(in) :: x
    end subroutine
  end interface
end module

submodule(name1) test
  module subroutine test2(x) ! Note the keyword `module`
    integer,intent(in):: x
    integer:: y 
    y = 2
    print *, x+y+z ,'from test2'
  end subroutine
end submodule

You can also reduce the amount of duplicated code using module procedure, as

module name1
  implicit none
  interface
    module subroutine test2(x)
      integer,intent(in) :: x
    end subroutine
  end interface
end module

submodule(name1) test
  module procedure test2
    integer:: y 
    y = 2
    print *, x+y+z ,'from test2'
  end procedure
end submodule

Using module procedure means you don't have to duplicate the arguments of the procedure (x) or their declarations integer,intent(in):: x.