problem with procedure pointers

[npenigaud]

Procedure pointers are used in recent versions of the semi-implicit. However, the following leads to a bug in Loki :
spcmnew_pb.F90:

SUBROUTINE SPCMNEW(YDGEOMETRY)

USE SPSI_MODNEW, ONLY : SPNSI
IMPLICIT NONE
PROCEDURE(SPNSI), POINTER :: SPNSIPTR
END SUBROUTINE SPCMNEW

launch.py:

from loki import Sourcefile,fgen
source=Sourcefile.from_file('spcmnew_pb.F90',preprocess=True)
spcmnew=source['spcmnew']
print(fgen(spcmnew.spec))

(SPNSI is an abstract interface for a subroutine, included in spsi_modnew.F90).

[reuterbal]

Thanks for reporting this, I can reproduce the problem:

from loki import Sourcefile
fcode = """
SUBROUTINE SPCMNEW
USE SPSI_MODNEW, ONLY : SPNSI
IMPLICIT NONE
PROCEDURE(SPNSI), POINTER :: SPNSIPTR
END SUBROUTINE SPCMNEW
"""
source = Sourcefile.from_source(fcode)
print(source.to_fortran())

This fails with an assertion in the fgen backend because the type information for SPNSI is missing:

File "/.../main/loki/backend/fgen.py", line 406, in visit_ProcedureDeclaration
    assert all(isinstance(t.dtype, ProcedureType) for t in types)

It works correctly if the type definition is provided to Loki, as in the following example:

fcode_module = """
MODULE SPSI_MODNEW
IMPLICIT NONE
INTERFACE
  SUBROUTINE SPNSI
  END SUBROUTINE SPNSI
END INTERFACE
END MODULE SPSI_MODNEW
"""
fcode = "..."
module = Sourcefile.from_source(fcode_module)
source = Sourcefile.from_source(fcode, definitions=module.definitions)
print(source.to_fortran())

This produces the correct output:

SUBROUTINE SPCMNEW ()
  USE SPSI_MODNEW, ONLY: SPNSI
  IMPLICIT NONE
  PROCEDURE(SPNSI), POINTER :: SPNSIPTR
END SUBROUTINE SPCMNEW

The fix is to allow also deferred type information for the procedure interface, for which the following seems to suffice:

diff --git a/loki/backend/fgen.py b/loki/backend/fgen.py
index 5ca129cf..090e3c3b 100644
--- a/loki/backend/fgen.py
+++ b/loki/backend/fgen.py
@@ -403,12 +403,15 @@ class FortranCodegen(Stringifier):
         # TODO: We can't fully compare procedure types, yet, but we can make at least sure
         # names match and other declared attributes are compatible
         ignore = ['dtype', 'shape', 'dimensions', 'symbols', 'source', 'initial']
-        assert all(isinstance(t.dtype, ProcedureType) for t in types)
+        assert all(isinstance(t.dtype, ProcedureType) or t.dtype == BasicType.DEFERRED for t in types)
         assert all(t.compare(types[0], ignore=ignore) for t in types)
         if isinstance(o.interface, DataType):
             assert all(t.dtype.return_type.dtype == o.interface for t in types)
         elif o.interface is not None:
-            assert all(t.dtype.name == o.interface for t in types)
+            if types[0].dtype == BasicType.DEFERRED:
+                assert all(t.dtype == BasicType.DEFERRED for t in types)
+            else:
+                assert all(t.dtype.name == o.interface for t in types)

         if o.external:
             # This is an EXTERNAL statement (i.e., a kind of forward declaration)

@npenigaud Can you please confirm that the fix works for you? Then I will file a PR with these changes later.

[npenigaud]

Yes, the fix works for me, thanks. Regards, N. Penigaud