Revert sorting of symbolic tags (#476)

* Revert sorting of symbolic tags

Sorting fails when symbolic tags contain bare classes (which can not be
compared most of the time).

The attached test case fails without this PR.

* undo doc

pytato/distributed/__init__.py

@@ -23,7 +23,7 @@
 .. class:: CommTagType
 
     A type representing a communication tag. Communication tags must be
-    hashable and totally ordered (and hence comparable).
+    hashable.
 
 .. class:: ShapeType
 

pytato/distributed/tags.py

@@ -62,10 +62,6 @@ def number_distributed_tags(
 
         This is a potentially heavyweight MPI-collective operation on
         *mpi_communicator*.
-
-    .. note::
-
-        This function requires that symbolic tags are comparable.
     """
     tags = frozenset({
             recv.comm_tag
@@ -106,7 +102,7 @@ def set_union(
         next_tag = base_tag
         assert isinstance(all_tags, frozenset)
 
-        for sym_tag in sorted(all_tags):
+        for sym_tag in all_tags:
             sym_tag_to_int_tag[sym_tag] = next_tag
             next_tag += 1
 

test/test_distributed.py

@@ -844,6 +844,48 @@ def _do_verify_distributed_partition(ctx_factory):
 # }}}
 
 
+# {{{ test symbolic tag numbering with bare classes
+
+class FooTag1:
+    pass
+
+
+class FooTag2:
+    pass
+
+
+def test_number_symbolic_tags_bare_classes(ctx_factory):
+    from mpi4py import MPI  # pylint: disable=import-error
+    comm = MPI.COMM_WORLD
+    from pytato.distributed.nodes import (staple_distributed_send,
+                make_distributed_recv)
+
+    rank = 0
+    size = 2
+
+    x = pt.make_placeholder("x", (4, 4), int)
+    y = pt.make_placeholder("y", (4, 4), int)
+
+    r1 = staple_distributed_send(x, dest_rank=(rank-1) % size,
+            comm_tag=FooTag1, stapled_to=make_distributed_recv(
+                src_rank=(rank+1) % size, comm_tag=FooTag1, shape=(4, 4),
+                dtype=int))
+
+    r2 = staple_distributed_send(y, dest_rank=(rank-1) % size,
+            comm_tag=FooTag2, stapled_to=make_distributed_recv(
+                src_rank=(rank+1) % size, comm_tag=FooTag2, shape=(4, 4),
+                dtype=int))
+
+    res = r1 + r2
+
+    outputs = pt.make_dict_of_named_arrays({"out": res})
+    partition = pt.find_distributed_partition(comm, outputs)
+
+    pt.number_distributed_tags(comm, partition, base_tag=4242)
+
+# }}}
+
+
 if __name__ == "__main__":
     if "RUN_WITHIN_MPI" in os.environ:
         run_test_with_mpi_inner()