Fortran mpi module: remove interface names

Fortran is a deceptively complicated language.  It turns out that it
is permissable to pass arrays of many sizes and shapes to subroutines
that expect 1-dimensional array parameters.  For example, a C
programmer might look at the following subroutine declaration and
assume that it means that the ARRAY_OF_REQUESTS parameter is a
1-dimensional array of any length:

```
MPI_WAITALL(COUNT, ARRAY_OF_REQUESTS, ARRAY_OF_STATUSES, IERROR)
    INTEGER COUNT, ARRAY_OF_REQUESTS(*),
              ARRAY_OF_STATUSES(MPI_STATUS_SIZE, *), IERROR
```

However, rules of the Fortran language allow the compiler to
effectively morph non-1-dimensional array source parameters to match,
for example, the 1-dimensional ARRAY_OF_REQUESTS dummy parameter.
Sometimes this will be done by copy-in-copy-out; other times, the
compiler can just swizzle the types to match because the source array
data is already contiguous in memory.

Regardless, there are several rules about when this type swizzling can
happen, and there are differences in the rules between when the target
subroutine in question is in a named interface such as:

```
INTERFACE FOO
  SUBROUTINE FOO(arg)
    INTEGER ARG(*)
  END SUBROUTINE FOO
END INTERFACE
```

versus when the subroutine is in an unnamed interface such as:

```
INTERFACE
  SUBROUTINE FOO(arg)
    INTEGER ARG(*)
  END SUBROUTINE FOO
END INTERFACE
```

I will not pretend to be a Fortran language expert and won't quote the
language rules here.  The short version is that unnamed interfaces
allow more flexible type swizzling.  For example, a user can pass a
2-dimensional INTEGER array to MPI_WAITALL's ARRAY_OF_REQUESTS
argument, and -- assuming that the 2D array is contiguous in memory --
the compiler will make the 2D array type match the 1D
ARRAY_OF_REQUESTS argument.  Open MPI will get a contiguous chunk of
memory of integers, so it doesn't know/care.

The MPI standard does not address this issue at all.  I.e., it doesn't
say whether passing N-dimensional parameters to subroutines like
MPI_WAITALL are permissable or not.  It also does not specify whether
interfaces need to be used, or if interfaces are used, whether they
need to be named or unnamed -- these are all implementation decisions.
However, there has been a lot of discussion about this in the Fortran
group at the MPI Forum over the last week; there will almost certainly
be an errata to MPI-4.0 and/or some text changes in MPI-4.1 to clarify
the situation.  I'm not going to speculate on the final language that
will get accepted by the Forum, but it seems like since Open MPI's
implentation decision to use named interfaces is perhaps the most
restrictive in terms of compiler swizzling functionality, we should
probably ease those restrictions so as not to violate the Law of Least
Astonishment from the user's perspective (who would expect that the
Fortran compiler will be able to swizzle array sizes and shapes).

As such, this commit removes all interface names from the Fortran
"mpi" bindings module where there's only a single subroutine in the
interface, and that subroutine name exactly matches the interface
name.  Note that this specifically excludes the following routines,
which have multiple subroutines in the interface (for two different
types of Fortran pointers):

* MPI_Alloc_mem
* MPI_Win_allocate
* MPI_Win_allocate_shared
* MPI_Win_shared_query

Deleting the interface names *may* cause ABI implications in some
compilers.  I have not exhaustively tested Fortran compilers to know
if this is an issue or not.  The safest thing to do is to implement
this change for Open MPI v5.0.0 where we're breaking lots of ABI
things as compared to prior versions of Open MPI.

Note that this issue does *not* affect the mpi_f08 module.  Using
named interfaces were distinctly specified in the MPI standard.

Also, this doesn't affect mpif.h, because Open MPI doesn't declare
most interfaces/subroutines in mpif.h.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

Author: jsquyres

ompi/mpi/fortran/use-mpi-ignore-tkr/mpi-ignore-tkr-file-interfaces.h.in

@@ -1,6 +1,6 @@
 ! -*- fortran -*-
 !
-! Copyright (c) 2006-2012 Cisco Systems, Inc.  All rights reserved.
+! Copyright (c) 2006-2021 Cisco Systems, Inc.  All rights reserved
 ! Copyright (c) 2007      Los Alamos National Security, LLC.  All rights
 !                         reserved.
 ! Copyright (c) 2012      The University of Tennessee and The University
@@ -17,7 +17,7 @@
 !
 ! $HEADER$
 
-interface MPI_Address
+interface
 
 subroutine MPI_Address(location, address, ierror)
   @OMPI_FORTRAN_IGNORE_TKR_PREDECL@ location
@@ -28,7 +28,7 @@ end subroutine MPI_Address
 
 end interface
 
-interface MPI_Attr_delete
+interface
 
 subroutine MPI_Attr_delete(comm, keyval, ierror)
   integer, intent(in) :: comm
@@ -38,7 +38,7 @@ end subroutine MPI_Attr_delete
 
 end interface
 
-interface MPI_Attr_get
+interface
 
 subroutine MPI_Attr_get(comm, keyval, attribute_val, flag, ierror)
   integer, intent(in) :: comm
@@ -50,7 +50,7 @@ end subroutine MPI_Attr_get
 
 end interface
 
-interface MPI_Attr_put
+interface
 
 subroutine MPI_Attr_put(comm, keyval, attribute_val, ierror)
   integer, intent(in) :: comm
@@ -61,7 +61,7 @@ end subroutine MPI_Attr_put
 
 end interface
 
-interface MPI_Errhandler_create
+interface
 
 subroutine MPI_Errhandler_create(function, errhandler, ierror)
   external :: function
@@ -71,7 +71,7 @@ end subroutine MPI_Errhandler_create
 
 end interface
 
-interface MPI_Errhandler_get
+interface
 
 subroutine MPI_Errhandler_get(comm, errhandler, ierror)
   integer, intent(in) :: comm
@@ -81,7 +81,7 @@ end subroutine MPI_Errhandler_get
 
 end interface
 
-interface MPI_Errhandler_set
+interface
 
 subroutine MPI_Errhandler_set(comm, errhandler, ierror)
   integer, intent(in) :: comm
@@ -91,7 +91,7 @@ end subroutine MPI_Errhandler_set
 
 end interface
 
-interface MPI_Keyval_create
+interface
 
 subroutine MPI_Keyval_create(copy_fn, delete_fn, keyval, extra_state, ierror)
   external :: copy_fn
@@ -103,7 +103,7 @@ end subroutine MPI_Keyval_create
 
 end interface
 
-interface MPI_Keyval_free
+interface
 
 subroutine MPI_Keyval_free(keyval, ierror)
   integer, intent(inout) :: keyval
@@ -112,7 +112,7 @@ end subroutine MPI_Keyval_free
 
 end interface
 
-interface MPI_Type_extent
+interface
 
 subroutine MPI_Type_extent(datatype, extent, ierror)
   integer, intent(in) :: datatype
@@ -122,7 +122,7 @@ end subroutine MPI_Type_extent
 
 end interface
 
-interface MPI_Type_hindexed
+interface
 
 subroutine MPI_Type_hindexed(count, array_of_blocklengths, array_of_displacements, oldtype, newtype&
         , ierror)
@@ -136,7 +136,7 @@ end subroutine MPI_Type_hindexed
 
 end interface
 
-interface MPI_Type_hvector
+interface
 
 subroutine MPI_Type_hvector(count, blocklength, stride, oldtype, newtype&
         , ierror)
@@ -150,7 +150,7 @@ end subroutine MPI_Type_hvector
 
 end interface
 
-interface MPI_Type_lb
+interface
 
 subroutine MPI_Type_lb(datatype, lb, ierror)
   integer, intent(in) :: datatype
@@ -160,7 +160,7 @@ end subroutine MPI_Type_lb
 
 end interface
 
-interface MPI_Type_struct
+interface
 
 subroutine MPI_Type_struct(count, array_of_blocklengths, array_of_displacements, array_of_types, newtype&
         , ierror)
@@ -174,7 +174,7 @@ end subroutine MPI_Type_struct
 
 end interface
 
-interface MPI_Type_ub
+interface
 
 subroutine MPI_Type_ub(datatype, ub, ierror)
   integer, intent(in) :: datatype

ompi/mpi/fortran/use-mpi-ignore-tkr/mpi-ignore-tkr-interfaces.h.in

@@ -2,14 +2,15 @@
 !
 ! Copyright (c) 2020      Research Organization for Information Science
 !                         and Technology (RIST).  All rights reserved.
+! Copyright (c) 2021      Cisco Systems, Inc.  All rights reserved
 ! $COPYRIGHT$
 !
 ! Additional copyrights may follow
 !
 ! $HEADER$
 
 
-interface MPI_Status_f082f
+interface
 
 subroutine MPI_Status_f082f(f08_status, f_status, ierror)
   use mpi_types
@@ -22,7 +23,7 @@ end subroutine MPI_Status_f082f
 end interface
 
 
-interface MPI_Status_f2f08
+interface
 
 subroutine MPI_Status_f2f08(f_status, f08_status, ierror)
   use mpi_types
@@ -35,7 +36,7 @@ end subroutine MPI_Status_f2f08
 end interface
 
 
-interface PMPI_Status_f082f
+interface
 
 subroutine PMPI_Status_f082f(f08_status, f_status, ierror)
   use mpi_types
@@ -48,7 +49,7 @@ end subroutine PMPI_Status_f082f
 end interface
 
 
-interface PMPI_Status_f2f08
+interface
 
 subroutine PMPI_Status_f2f08(f_status, f08_status, ierror)
   use mpi_types

ompi/mpi/fortran/use-mpi-ignore-tkr/mpi-ignore-tkr-removed-interfaces.h.in

@@ -1,6 +1,6 @@
 ! -*- fortran -*-
 !
-! Copyright (c) 2014 Cisco Systems, Inc.  All rights reserved.
+! Copyright (c) 2014-2021 Cisco Systems, Inc.  All rights reserved
 ! $COPYRIGHT$
 !
 ! Additional copyrights may follow
@@ -17,6 +17,7 @@
 ! below.
 !
 
+! This interface requires a name because there are multiple subroutines.
 interface MPI_Win_allocate
 
 subroutine MPI_Win_allocate(size, disp_unit, info, comm, &
@@ -46,6 +47,7 @@ end subroutine MPI_Win_allocate_cptr
 end interface
 
 
+! This interface requires a name because there are multiple subroutines.
 interface MPI_Win_allocate_shared
 
 subroutine MPI_Win_allocate_shared(size, disp_unit, info, comm, &
@@ -75,6 +77,7 @@ end subroutine MPI_Win_allocate_shared_cptr
 end interface
 
 
+! This interface requires a name because there are multiple subroutines.
 interface MPI_Win_shared_query
 
 subroutine MPI_Win_shared_query(win, rank, size, disp_unit, baseptr,&