A temporary quick fix for dataclass serialization (#500)

This quick fix will be removed when proper dataclass serialization 
support is added to dill. This is just here to allow for better support, 
at least for now. dataclasses pickled with this PR will be unpicklable 
by future versions of dill, but the future versions of dill will be able 
to be automatically use the newer features in dataclasses.py that were 
not available in older versions of Python. That forward compatibility 
features is not present in this PR.

dill/_dill.py

@@ -277,6 +277,10 @@ def get_file_type(*args, **kwargs):
 from collections import OrderedDict
 
 import inspect
+import dataclasses
+
+from pickle import GLOBAL
+
 
 ### Shims for different versions of Python and dill
 class Sentinel(object):
@@ -2258,6 +2262,33 @@ def save_capsule(pickler, obj):
 else:
     _testcapsule = None
 
+
+#############################
+# A quick fix for issue #500
+# This should be removed when a better solution is found.
+
+if hasattr(dataclasses, "_HAS_DEFAULT_FACTORY_CLASS"):
+    @register(dataclasses._HAS_DEFAULT_FACTORY_CLASS)
+    def save_dataclasses_HAS_DEFAULT_FACTORY_CLASS(pickler, obj):
+        pickler.write(GLOBAL + b"dataclasses\n_HAS_DEFAULT_FACTORY\n")
+
+if hasattr(dataclasses, "MISSING"):
+    @register(type(dataclasses.MISSING))
+    def save_dataclasses_MISSING_TYPE(pickler, obj):
+        pickler.write(GLOBAL + b"dataclasses\nMISSING\n")
+
+if hasattr(dataclasses, "KW_ONLY"):
+    @register(type(dataclasses.KW_ONLY))
+    def save_dataclasses_KW_ONLY_TYPE(pickler, obj):
+        pickler.write(GLOBAL + b"dataclasses\nKW_ONLY\n")
+
+if hasattr(dataclasses, "_FIELD_BASE"):
+    @register(dataclasses._FIELD_BASE)
+    def save_dataclasses_FIELD_BASE(pickler, obj):
+        pickler.write(GLOBAL + b"dataclasses\n" + obj.name.encode() + b"\n")
+
+#############################
+
 # quick sanity checking
 def pickles(obj,exact=False,safe=False,**kwds):
     """

tests/test_dataclasses.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python
+#
+# Author: Mike McKerns (mmckerns @caltech and @uqfoundation)
+# Author: Anirudh Vegesana (avegesan@cs.stanford.edu)
+# Copyright (c) 2022 The Uncertainty Quantification Foundation.
+# License: 3-clause BSD.  The full license text is available at:
+#  - https://github.com/uqfoundation/dill/blob/master/LICENSE
+"""
+test pickling a dataclass
+"""
+
+import dill
+import dataclasses
+
+def test_dataclasses():
+    # Issue #500
+    @dataclasses.dataclass
+    class A:
+        x: int
+        y: str
+
+    @dataclasses.dataclass
+    class B:
+        a: A
+
+    a = A(1, "test")
+    before = B(a)
+    save = dill.dumps(before)
+    after = dill.loads(save)
+    assert before != after # classes don't match
+    assert before == B(A(**dataclasses.asdict(after.a)))
+    assert dataclasses.asdict(before) == dataclasses.asdict(after)
+
+if __name__ == '__main__':
+    test_dataclasses()