added default params rng to .apply

flax/core/scope.py

@@ -1074,9 +1074,19 @@ def apply(
   def wrapper(
     variables: VariableDict,
     *args,
-    rngs: Optional[RNGSequences] = None,
+    rngs: Optional[Union[PRNGKey, RNGSequences]] = None,
     **kwargs,
   ) -> Union[Any, Tuple[Any, Union[VariableDict, Dict[str, Any]]]]:
+    if rngs is not None:
+      if not _is_valid_rng(rngs) and not _is_valid_rngs(rngs):
+        raise ValueError(
+          'The ``rngs`` argument passed to an apply function should be a '
+          '``jax.PRNGKey`` or a dictionary mapping strings to '
+          '``jax.PRNGKey``.'
+        )
+      if not isinstance(rngs, (dict, FrozenDict)):
+        rngs = {'params': rngs}
+
     # Try to detect if user accidentally passed {'params': {'params': ...}.
     if (
       'params' in variables
@@ -1118,10 +1128,10 @@ def wrapper(rngs, *args, **kwargs) -> Tuple[Any, VariableDict]:
     if not _is_valid_rng(rngs) and not _is_valid_rngs(rngs):
       raise ValueError(
         'First argument passed to an init function should be a '
-        '`jax.PRNGKey` or a dictionary mapping strings to '
-        '`jax.PRNGKey`.'
+        '``jax.PRNGKey`` or a dictionary mapping strings to '
+        '``jax.PRNGKey``.'
       )
-    if not isinstance(rngs, dict):
+    if not isinstance(rngs, (dict, FrozenDict)):
       rngs = {'params': rngs}
     init_flags = {**(flags if flags is not None else {}), 'initializing': True}
     return apply(fn, mutable=mutable, flags=init_flags)(
@@ -1217,7 +1227,7 @@ def _is_valid_rng(rng: Array):
   return True
 
 
-def _is_valid_rngs(rngs: RNGSequences):
+def _is_valid_rngs(rngs: Union[PRNGKey, RNGSequences]):
   if not isinstance(rngs, (FrozenDict, dict)):
     return False
   for key, val in rngs.items():

flax/linen/module.py

@@ -2041,7 +2041,7 @@ def apply(
     self,
     variables: VariableDict,
     *args,
-    rngs: Optional[RNGSequences] = None,
+    rngs: Optional[Union[PRNGKey, RNGSequences]] = None,
     method: Union[Callable[..., Any], str, None] = None,
     mutable: CollectionFilter = False,
     capture_intermediates: Union[bool, Callable[['Module', str], bool]] = False,
@@ -2115,6 +2115,14 @@ def apply(
     """
     Module._module_checks(self)
 
+    if rngs is not None and not isinstance(rngs, dict):
+      if not core.scope._is_valid_rng(rngs):
+        raise errors.InvalidRngError(
+          'RNGs should be of shape (2,) or PRNGKey in Module '
+          f'{self.__class__.__name__}, but rngs are: {rngs}'
+        )
+      rngs = {'params': rngs}
+
     if isinstance(method, str):
       attribute_name = method
       method = getattr(self, attribute_name)

tests/linen/linen_module_test.py

@@ -815,6 +815,43 @@ def __call__(self, x):
     trace = mlp.apply(variables, x)
     self.assertEqual(trace, expected_trace)
 
+  def test_default_params_rng_equivalence(self):
+    class Model(nn.Module):
+      @nn.compact
+      def __call__(self, x, add_dropout=False, add_noise=False):
+        x = nn.Dense(16)(x)
+        x = nn.Dropout(0.5)(x, deterministic=not add_dropout)
+        if add_noise:
+          x += jax.random.normal(self.make_rng('params'))
+        return x
+
+    model = Model()
+    key0, key1, key2 = jax.random.split(jax.random.key(0), 3)
+    x = jax.random.normal(key0, (10, 8))
+
+    with self.assertRaisesRegex(ValueError, 'First argument passed to an init function should be a ``jax.PRNGKey``'):
+      model.init({'params': 'test'}, x)
+    with self.assertRaisesRegex(errors.InvalidRngError, 'RNGs should be of shape \\(2,\\) or PRNGKey in Module Model, but rngs are: test'):
+      model.init('test', x)
+    with self.assertRaisesRegex(errors.InvalidRngError, 'Dropout_0 needs PRNG for "dropout"'):
+      model.init(key1, x, add_dropout=True)
+
+    v = model.init({'params': key1}, x)
+    v2 = model.init(key1, x)
+    jax.tree_map(np.testing.assert_allclose, v, v2)
+
+    out = model.apply(v, x, add_noise=True, rngs={'params': key2})
+    out2 = model.apply(v, x, add_noise=True, rngs=key2)
+    np.testing.assert_allclose(out, out2)
+
+    with self.assertRaisesRegex(ValueError, 'The ``rngs`` argument passed to an apply function should be a ``jax.PRNGKey``'):
+      model.apply(v, x, rngs={'params': 'test'})
+    with self.assertRaisesRegex(errors.InvalidRngError, 'RNGs should be of shape \\(2,\\) or PRNGKey in Module Model, but rngs are: test'):
+      model.apply(v, x, rngs='test')
+    with self.assertRaisesRegex(errors.InvalidRngError, 'Dropout_0 needs PRNG for "dropout"'):
+      model.apply(v, x, add_dropout=True, rngs=key2)
+
+
   def test_module_apply_method(self):
     class Foo(nn.Module):
       not_callable: int = 1