[Bug fortran/47448] New: Accepts invalid ASSIGNMENT(=) which overrides intrinsic assignment

["burnus at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47448

           Summary: Accepts invalid ASSIGNMENT(=) which overrides
                    intrinsic assignment
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid, diagnostic
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: burnus@gcc.gnu.org


bd satish shows at http://gcc.gnu.org/ml/fortran/2011-01/msg00209.html an
example, which is accepted but invalid:


interface assignment(=)
   module procedure return_char_array
end interface

contains

  subroutine return_char_array(outstr,instr)
    character, allocatable, intent(out) ::  outstr(:)
    character(len=*), intent(in) :: instr


The issue is that this interface would override an intrinsic assignment, which
is not allowed. Or in word of the Fortran 2008 standard on "12.4.3.4.3 Defined
assignments":

"The first argument shall have INTENT (OUT) or INTENT (INOUT) and the second
argument shall have INTENT (IN). Either the second argument shall be an array
whose rank diers from that of the first argument, the declared types and kind
type parameters of the arguments shall not conform as specified in Table 7.8,
or the first argument shall be of derived type."


As those constraints do not have a C number, the compiler is not required to
diagnose this, but as quality of implementation it should.

Other compilers:
- g95: Error: Operator interface at (1) conflicts with the intrinsic operation
- PathScale: Error: This specific interface "RETURN_CHAR_ARRAY" conflicts with
the intrinsic use of "=".

NAG shows a completely bogus error and ifort compiles and used the defined
interface.