Fix generic dataclasses with bound parameters.

This alters the way in which mappable dataclasses are created in order to fix a
crash when a mappable, frozen generic dataclass is instantiated with a bound
type parameter.

PiperOrigin-RevId: 521409933

chex/_src/dataclass.py

@@ -27,32 +27,56 @@
 _RESERVED_DCLS_FIELD_NAMES = frozenset(("from_tuple", "replace", "to_tuple"))
 
 
-def mappable_dataclass(cls):
-  """Exposes dataclass as ``collections.abc.Mapping`` descendent.
+def _make_mappable(cls):
+  """Create type that implements and inherits from ``collections.abc.Mapping``.
 
+  Note that this does not require the class to be a dataclass, as it is supposed
+  to be applied before creating the dataclass.
+  
   Allows to traverse dataclasses in methods from `dm-tree` library.
 
-  NOTE: changes dataclasses constructor to dict-type
-  (i.e. positional args aren't supported; however can use generators/iterables).
-
   Args:
-    cls: A dataclass to mutate.
+    cls: A class to use as a base for the new type.
 
   Returns:
-    Mutated dataclass implementing ``collections.abc.Mapping`` interface.
+    Class implementing  and inheriting from ``collections.abc.Mapping``.
   """
-  if not dataclasses.is_dataclass(cls):
-    raise ValueError(f"Expected dataclass, got {cls} (change wrappers order?).")
-
   # Define methods for compatibility with `collections.abc.Mapping`.
   setattr(cls, "__getitem__", lambda self, x: self.__dict__[x])
   setattr(cls, "__len__", lambda self: len(self.__dict__))
   setattr(cls, "__iter__", lambda self: iter(self.__dict__))
 
-  # Update constructor.
-  orig_init = cls.__init__
-  all_fields = set(f.name for f in cls.__dataclass_fields__.values())
-  init_fields = [f.name for f in cls.__dataclass_fields__.values() if f.init]
+  # Update base class to derive from Mapping
+  dct = dict(cls.__dict__)
+  if "__dict__" in dct:
+    dct.pop("__dict__")  # Avoid self-references.
+
+  # Remove object from the sequence of base classes. Deriving from both Mapping
+  # and object will cause a failure to create a MRO for the updated class
+  bases = tuple(b for b in cls.__bases__ if b != object)
+  return type(cls.__name__, bases + (collections.abc.Mapping,), dct)
+
+
+def _make_kw_only_dataclass_init(dcls):
+  """Create wrapped dataclass initializer that requires keyword-only arguments.
+  
+  This should be equivalent to passing `kw_only=True` when creating the
+  dataclass in Python <= 3.10.
+  
+  Args:
+    dcls: the dataclass to take the constructor from.
+  
+  Returns:
+    Initializer wrapping the original initializer but which requires
+    keyword-only arguments.
+  
+  Throws:
+    ValueError: if all required arguments are not provided as keyword-only.
+  
+  """
+  orig_init = dcls.__init__
+  all_fields = set(f.name for f in dcls.__dataclass_fields__.values())
+  init_fields = [f.name for f in dcls.__dataclass_fields__.values() if f.init]
 
   @functools.wraps(orig_init)
   def new_init(self, *orig_args, **orig_kwargs):
@@ -69,17 +93,28 @@ def new_init(self, *orig_args, **orig_kwargs):
     valid_kwargs = {k: v for k, v in all_kwargs.items() if k in init_fields}
     orig_init(self, **valid_kwargs)
 
-  cls.__init__ = new_init
+  return new_init
 
-  # Update base class to derive from Mapping
-  dct = dict(cls.__dict__)
-  if "__dict__" in dct:
-    dct.pop("__dict__")  # Avoid self-references.
 
-  # Remove object from the sequence of base classes. Deriving from both Mapping
-  # and object will cause a failure to create a MRO for the updated class
-  bases = tuple(b for b in cls.__bases__ if b != object)
-  cls = type(cls.__name__, bases + (collections.abc.Mapping,), dct)
+def mappable_dataclass(cls):
+  """Exposes dataclass as ``collections.abc.Mapping`` descendent.
+
+  Allows to traverse dataclasses in methods from `dm-tree` library.
+
+  NOTE: changes dataclasses constructor to dict-type
+  (i.e. positional args aren't supported; however can use generators/iterables).
+
+  Args:
+    cls: A dataclass to mutate.
+
+  Returns:
+    Mutated dataclass implementing ``collections.abc.Mapping`` interface.
+  """
+  if not dataclasses.is_dataclass(cls):
+    raise ValueError(f"Expected dataclass, got {cls} (change wrappers order?).")
+
+  cls = _make_mappable(cls)
+  cls.__init__ = _make_kw_only_dataclass_init(cls)
   return cls
 
 
@@ -159,6 +194,14 @@ def __init__(
   def __call__(self, cls):
     """Forwards class to dataclasses's wrapper and registers it with JAX."""
 
+    if self.mappable_dataclass:
+      cls = _make_mappable(cls)
+      # We remove `collection.abc.Mapping` mixin methods here to allow
+      # fields with these names.
+      for attr in ("values", "keys", "get", "items"):
+        setattr(cls, attr, None)  # redefine
+        delattr(cls, attr)        # delete
+
     # Remove once https://github.com/python/cpython/pull/24484 is merged.
     for base in cls.__bases__:
       if (dataclasses.is_dataclass(base) and
@@ -172,6 +215,7 @@ def __call__(self, cls):
         repr=self.repr,
         eq=self.eq,
         order=self.order,
+        kw_only=self.mappable_dataclass,
         unsafe_hash=self.unsafe_hash,
         frozen=self.frozen)
     # pytype: enable=wrong-keyword-args
@@ -182,14 +226,6 @@ def __call__(self, cls):
       raise ValueError(f"The following dataclass fields are disallowed: "
                        f"{invalid_fields} ({dcls}).")
 
-    if self.mappable_dataclass:
-      dcls = mappable_dataclass(dcls)
-      # We remove `collection.abc.Mapping` mixin methods here to allow
-      # fields with these names.
-      for attr in ("values", "keys", "get", "items"):
-        setattr(dcls, attr, None)  # redefine
-        delattr(dcls, attr)        # delete
-
     def _from_tuple(args):
       return dcls(zip(dcls.__dataclass_fields__.keys(), args))
 
@@ -212,6 +248,9 @@ def _setstate(self, state):
       self.__dict__.update(state)
 
     orig_init = dcls.__init__
+    is_mappable_dataclass = self.mappable_dataclass
+    if self.mappable_dataclass:
+      kw_only_init = _make_kw_only_dataclass_init(dcls)
 
     # Patch object's __init__ such that the class is registered on creation if
     # it is not registered on deserialization.
@@ -220,7 +259,11 @@ def _init(self, *args, **kwargs):
       if not class_self.registered:
         register_dataclass_type_with_jax_tree_util(dcls)
         class_self.registered = True
-      return orig_init(self, *args, **kwargs)
+
+      if is_mappable_dataclass:
+        return kw_only_init(self, *args, **kwargs)
+      else:
+        return orig_init(self, *args, **kwargs)
 
     setattr(dcls, "from_tuple", _from_tuple)
     setattr(dcls, "to_tuple", _to_tuple)

chex/_src/dataclass_test.py

@@ -539,19 +539,24 @@ class Bar:
     self.assertLen(jax.tree_util.tree_flatten(Bar())[0], 2)
 
   @parameterized.named_parameters(
-      ('mappable', True),
-      ('not_mappable', False),
+      ('mappable_frozen', True, True),
+      ('not_mappable_frozen', False, True),
+      ('mappable_not_frozen', True, False),
+      ('not_mappable_not_frozen', False, False),
   )
-  def test_generic_dataclass(self, mappable):
+  def test_generic_dataclass(self, mappable, frozen):
     T = TypeVar('T')
 
-    @chex_dataclass(mappable_dataclass=mappable)
+    @chex_dataclass(mappable_dataclass=mappable, frozen=frozen)
     class GenericDataclass(Generic[T]):
       a: T  # pytype: disable=invalid-annotation  # enable-bare-annotations
 
     obj = GenericDataclass(a=np.array([1.0, 1.0]))
     asserts.assert_tree_all_close(obj.a, 1.0)
 
+    obj = GenericDataclass[np.array](a=np.array([1.0, 1.0]))
+    asserts.assert_tree_all_close(obj.a, 1.0)
+
   def test_mappable_eq_override(self):
 
     @chex_dataclass(mappable_dataclass=True)