Convert increment_dat_version to abstract on DataCarrier

The inheritance chain for Dat and Global puts VecAccessMixin
(rightly) behind DataCarrier. This means that by MRO, the
increment_dat_version method provided on DataCarrier will be used,
which is a null operation. I think this makes sense, given that not all
classes use this. However, because we're providing
increment_dat_version as an override through VecAccessMixin, we need to
explicitly refer to it in the inheriting classes.

firedrake/preconditioners/patch.py

@@ -127,6 +127,9 @@ def _wrapper_cache_key_(self):
     def __call__(self, access, map_=None):
         return LocalDatLegacyArg(self, map_, access)
 
+    def increment_dat_version(self):
+        pass
+
 
 register_petsc_function("MatSetValues")
 

pyop2/types/dat.py

@@ -725,6 +725,9 @@ def __init__(self, dat, index):
                                       dtype=dat.dtype,
                                       name="view[%s](%s)" % (index, dat.name))
 
+    def increment_dat_version(self):
+        pass
+
     @utils.cached_property
     def _kernel_args_(self):
         return self._parent._kernel_args_
@@ -841,6 +844,9 @@ def vec_context(self, access):
         if access is not Access.READ:
             self.halo_valid = False
 
+    def increment_dat_version(self):
+        VecAccessMixin.increment_dat_version(self)
+
 
 class MixedDat(AbstractDat, VecAccessMixin):
     r"""A container for a bag of :class:`Dat`\s.

pyop2/types/data_carrier.py

@@ -44,6 +44,7 @@ def cdim(self):
         the product of the dim tuple."""
         return self._cdim
 
+    @abc.abstractmethod
     def increment_dat_version(self):
         pass
 

pyop2/types/glob.py

@@ -399,6 +399,9 @@ def vec_context(self, access):
             data = self._data
             self.comm.Bcast(data, 0)
 
+    def increment_dat_version(self):
+        VecAccessMixin.increment_dat_version(self)
+
 
 # has no comm, can only be READ
 class Constant(SetFreeDataCarrier):
@@ -464,3 +467,6 @@ def duplicate(self):
             dtype=self.dtype,
             name=self.name
         )
+
+    def increment_dat_version(self):
+        pass

pyop2/types/mat.py

@@ -550,6 +550,9 @@ def __repr__(self):
         return "Mat(%r, %r, %r)" \
                % (self._sparsity, self._datatype, self._name)
 
+    def increment_dat_version(self):
+        pass
+
 
 class Mat(AbstractMat):
     """OP2 matrix data. A Mat is defined on a sparsity pattern and holds a value