Interfaces in functions/subroutines should not be extracted, e.g. in

  SUBROUTINE foo(n)
    USE ISO_C_BINDING

    INTEGER, INTENT(out)

    INTERFACE
      FUNCTION c_foo() BIND(C, NAME="foo")
      END FUNCTION
    END INTERFACE

    n = c_foo()
  END SUBROUTINE

the c_foo interface should not be extracted and listed as interface by default (EXTRACT_PRIVATE=NO). It is not globally accessible.

Also, an unnamed interface as

  MODULE iface
    INTERFACE
      SUBROUTINE xyz(a, b, c)
        INTEGER :: a, b, c
      END SUBROUTINE
  END MODULE

has the name XYZ. In fortranscanner.l, line 421 (r749), one finds the comment:

  "// interface without name, must be inside subprog"

which is incorrect. The above example is perfectly valid. The name may be used to facilitate overloading and provide a generic name to different prototypes/interfaces, e.g.

  MODULE iface
    INTERFACE xyz
      SUBROUTINE xyz_sngl(x)
        REAL(4) :: x
      END SUBROUTINE
      SUBROUTINE xyz_dbl(x)
        REAL(8) :: x
      END SUBROUTINE
  END MODULE

Here, XYZ is the generic name of the interface for XYZ_SNGL and XYZ_DBL.