[nnx] disallow Array leaves

Numpy and JAX Array's are no longer consider state leaves. This makes the structure of the State completely determined by Variables, which apart from being more predictable it produces structural stability invariant to leaf type changes which let to issues such as #4142.

```python
class Foo(nnx.Module):
  def __init__(self):
    self.a = jnp.array(1) # no longer allowed, instead...
    self.b = nnx.Param(jnp.array(1)) # just use Variables
```

Also migrates all remaining tests from pytest to absl to ensure they are tested correctly internally.

PiperOrigin-RevId: 671372717

flax/nnx/nnx/graph.py

@@ -50,17 +50,18 @@
 Leaf = tp.TypeVar('Leaf')
 AuxData = tp.TypeVar('AuxData')
 
-StateLeaf = tp.Union[VariableState[tp.Any], np.ndarray, jax.Array]
+StateLeaf = VariableState[tp.Any]
+NodeLeaf = VariableState[tp.Any]
 GraphState = State[Key, StateLeaf]
 GraphFlatState = FlatState[StateLeaf]
 
 
 def is_state_leaf(x: tp.Any) -> tpe.TypeGuard[StateLeaf]:
-  return isinstance(x, (VariableState, np.ndarray, jax.Array))
+  return isinstance(x, VariableState)
 
 
-def is_node_leaf(x: tp.Any) -> tpe.TypeGuard[StateLeaf]:
-  return isinstance(x, (Variable, np.ndarray, jax.Array))
+def is_node_leaf(x: tp.Any) -> tpe.TypeGuard[NodeLeaf]:
+  return isinstance(x, Variable)
 
 
 class _HashById(tp.Hashable, tp.Generic[A]):
@@ -416,6 +417,11 @@ def _graph_flatten(
       flat_state[(*path, key)] = value
       leaves.append((key, None))
     else:
+      if isinstance(value, (jax.Array, np.ndarray)):
+        path_str = '/'.join(map(str, (*path, key)))
+        raise ValueError(
+            f'Arrays leaves are not supported, at {path_str!r}: {value}'
+        )
       static_fields.append((key, value))
 
   nodedef = NodeDef.create(

flax/nnx/nnx/training/optimizer.py

@@ -133,7 +133,7 @@ def __init__(
     self.step = OptState(jnp.array(0, dtype=jnp.uint32))
     self.model = model
     self.tx = tx
-    self.opt_state = tx.init(nnx.state(model, wrt))
+    self.opt_state = OptState(tx.init(nnx.state(model, wrt)))
     self.wrt = wrt
 
   def split(self, *filters: filterlib.Filter):
@@ -198,10 +198,10 @@ def update(self, grads):
     """
     state = nnx.state(self.model, self.wrt)
 
-    updates, new_opt_state = self.tx.update(grads, self.opt_state, state)
+    updates, new_opt_state = self.tx.update(grads, self.opt_state.value, state)
     new_params = optax.apply_updates(state, updates)
     assert isinstance(new_params, nnx.State)
 
     self.step.value += 1
     nnx.update(self.model, new_params)
-    self.opt_state = new_opt_state
+    self.opt_state.value = new_opt_state

flax/nnx/tests/deprecated_transforms_test.py

@@ -368,3 +368,6 @@ def __call__(self, x: jax.Array) -> jax.Array:
     y = module(x)
 
     assert y.shape == (1, 5, 3)
+
+if __name__ == '__main__':
+  absltest.main()

flax/nnx/tests/filters_test.py

@@ -12,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-
 from absl.testing import absltest
 
 from flax import nnx
@@ -30,4 +29,7 @@ def __init__(self, rngs):
     head_state = nnx.state(model, nnx.PathContains('head'))
 
     self.assertIn('head', head_state)
-    self.assertNotIn('backbone', head_state)
+    self.assertNotIn('backbone', head_state)
+
+if __name__ == '__main__':
+  absltest.main()

flax/nnx/tests/graph_utils_test.py

@@ -12,16 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from collections.abc import Callable
 import dataclasses
 from functools import partial
 from threading import Thread
 from typing import Any
 
-from absl.testing import absltest
+from absl.testing import absltest, parameterized
 from flax import linen, nnx, struct
 import jax
 import jax.numpy as jnp
-import pytest
 
 
 class StatefulLinear(nnx.Module):
@@ -77,7 +77,7 @@ def test_unflatten_empty(self):
 
     graphdef, state = nnx.split(g)
 
-    with pytest.raises(ValueError, match='Expected key'):
+    with self.assertRaisesRegex(ValueError, 'Expected key'):
       nnx.graph.unflatten(graphdef, nnx.State({}))
 
   def test_update_dynamic(self):
@@ -109,8 +109,8 @@ def test_update_static_inconsistent_types(self):
     g = [a, 3, a, nnx.Param(4)]
     g2 = [a, a, 3, nnx.Param(4)]
 
-    with pytest.raises(
-      ValueError, match='Trying to update a node with a different type'
+    with self.assertRaisesRegex(
+      ValueError, 'Trying to update a node with a different type'
     ):
       nnx.graph.graph_update_static(g, g2)
 
@@ -130,7 +130,7 @@ def test_update_static_add_shared_error(self):
     g = nnx.List([a, 3, a, nnx.Param(4)])
     g2 = nnx.List([a, 3, a, nnx.Param(4), a])
 
-    with pytest.raises(ValueError, match='Trying to add a new node at path'):
+    with self.assertRaisesRegex(ValueError, 'Trying to add a new node at path'):
       nnx.graph.graph_update_static(g, g2)
 
   def test_module_list(self):
@@ -428,10 +428,10 @@ def f_pure(graphdef: nnx.graph.GraphDef[Foo], state):
   def test_call_jit_update(self):
     class Counter(nnx.Module):
       def __init__(self):
-        self.count = jnp.zeros(())
+        self.count = nnx.Param(jnp.zeros(()))
 
       def inc(self):
-        self.count += 1
+        self.count.value += 1
         return 1
 
     graph_state = nnx.split(Counter())
@@ -447,7 +447,7 @@ def update(graph_state: nnx.PureState[Counter]):
 
     counter = nnx.merge(*graph_state)
 
-    self.assertEqual(counter.count, 2)
+    self.assertEqual(counter.count.value, 2)
 
   def test_stateful_linear(self):
     linear = StatefulLinear(3, 2, nnx.Rngs(0))
@@ -714,7 +714,7 @@ def test_to_tree_consistent_prefix(self):
     pure_tree = nnx.to_tree(impure_tree, prefix=prefix)
 
     prefix = (0, None, 1)
-    with pytest.raises(ValueError, match='Inconsistent aliasing detected'):
+    with self.assertRaisesRegex(ValueError, 'Inconsistent aliasing detected'):
       nnx.to_tree(impure_tree, prefix=prefix)
 
   def test_simple_vmap(self):
@@ -798,12 +798,24 @@ class SimplePyTreeModule(nnx.Module, experimental_pytree=True):
   pass
 
 
-@pytest.mark.parametrize(['x'], [(SimpleModule(),), (SimplePyTreeModule(),)])
-def test_threading(x: nnx.Module):
-  class MyThread(Thread):
-    def run(self) -> None:
-      nnx.graph.split(x)
+class TestThreading(parameterized.TestCase):
 
-  thread = MyThread()
-  thread.start()
-  thread.join()
+  @parameterized.parameters(
+      (SimpleModule,),
+      (SimplePyTreeModule,),
+  )
+  def test_threading(self, module_fn: Callable[[], nnx.Module]):
+    x = module_fn()
+
+    class MyThread(Thread):
+
+      def run(self) -> None:
+        nnx.graph.split(x)
+
+    thread = MyThread()
+    thread.start()
+    thread.join()
+
+
+if __name__ == '__main__':
+  absltest.main()

flax/nnx/tests/module_test.py

@@ -12,21 +12,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import dataclasses
 from copy import deepcopy
+import dataclasses
 from typing import Any, TypeVar
 
+from absl.testing import absltest
+from flax import nnx
 import jax
 import jax.numpy as jnp
 import numpy as np
-import pytest
-
-from flax import nnx
 
 A = TypeVar('A')
 
 
-class TestModule:
+class TestModule(absltest.TestCase):
   def test_has_module_state(self):
     class Foo(nnx.Module): ...
 
@@ -39,9 +38,9 @@ def test_trace_level(self):
 
     @jax.jit
     def f():
-      with pytest.raises(
-        nnx.errors.TraceContextError,
-        match="Cannot mutate 'Dict' from different trace level",
+      with self.assertRaisesRegex(
+          nnx.errors.TraceContextError,
+          "Cannot mutate 'Dict' from different trace level",
       ):
         m.a = 2
 
@@ -265,7 +264,7 @@ def __call__(self, x):
 
     m = Foo()
 
-    with pytest.raises(ValueError, match='to be a Variable, got'):
+    with self.assertRaisesRegex(ValueError, 'to be a Variable, got'):
       m(2)
 
   def test_sow_wrong_collection(self):
@@ -280,7 +279,7 @@ def __call__(self, x):
 
     m = Foo()
 
-    with pytest.raises(ValueError, match='to be of type'):
+    with self.assertRaisesRegex(ValueError, 'to be of type'):
       m(2)
 
   def test_update_static_state_submodules(self):
@@ -466,9 +465,12 @@ def __init__(self, din, dout, *, rngs: nnx.Rngs):
 
     block = Block(2, 5, rngs=nnx.Rngs(0))
 
-    with pytest.raises(
-      ValueError,
-      match="Could not find at least one instance of the following attributes: {'unknown'}",
+    with self.assertRaisesRegex(
+        ValueError,
+        (
+            'Could not find at least one instance of the following attributes:'
+            " {'unknown'}"
+        ),
     ):
       block.set_attributes(
         deterministic=True, use_running_average=True, unknown=True
@@ -662,26 +664,10 @@ def __init__(self, *, rngs: nnx.Rngs):
     assert modules[1][0] == 'linear'
     assert isinstance(modules[1][1], nnx.Linear)
 
-  def test_array_in_module(self):
-    class Foo(nnx.Module):
-      def __init__(self):
-        self.a = jnp.array(1.0)
-
-    foo = Foo()
-
-    graphdef, state = nnx.split(foo)
-
-    assert isinstance(state, nnx.State)
-    assert isinstance(state.a, jax.Array)
-
-    foo2 = nnx.merge(graphdef, state)
-
-    assert isinstance(foo2.a, jax.Array)
-
   def test_state_in_module(self):
     class Foo(nnx.Module):
       def __init__(self):
-        self.a = nnx.State({'b': jnp.array(1.0)})
+        self.a = nnx.State({'b': nnx.Param(jnp.array(1.0))})
 
     foo = Foo()
 
@@ -693,3 +679,6 @@ def __init__(self):
     foo2 = nnx.merge(graphdef, state)
 
     assert isinstance(foo2.a, nnx.State)
+
+if __name__ == '__main__':
+  absltest.main()