Fix bug that assumed frozen-dict keys were strings.

flax/core/frozen_dict.py

@@ -322,7 +322,7 @@ def _frozen_dict_state_dict(xs):
 
 
 def _restore_frozen_dict(xs, states):
-  diff = set(map(str, xs.keys())).difference(states.keys())
+  diff = set(map(str, xs.keys())).difference(map(str, states.keys()))
   if diff:
     raise ValueError(
       'The target dict keys and state dict keys do not match, target dict'

tests/linen/linen_module_test.py

@@ -17,6 +17,7 @@
 import contextlib
 import copy
 import dataclasses
+import enum
 import functools
 import gc
 import inspect
@@ -3037,6 +3038,17 @@ def __call__(self, x):
     self.assertIn('next_layer_1', variables['params'])
     self.assertNotIn('child_template', variables['params'])
 
+  def test_nonstring_keys_in_dict_on_module(self):
+    class MyEnum(str, enum.Enum):
+      a = 'a'
+      b = 'b'
+    class MyModule(nn.Module):
+      config: dict[MyEnum, int]
+      def __call__(self, inputs):
+        return inputs
+    module = MyModule(config={MyEnum.a: 1, MyEnum.b: 2})
+    variables = module.init(jax.random.key(0), jnp.zeros([0]))
+
 
 class FrozenDictTests(absltest.TestCase):
   def test_frozendict_flag(self):