Fix __post_init__ detection in Module

equinox/_module.py

@@ -250,11 +250,12 @@ def __new__(
             else:
                 assert name == "Module"
                 has_dataclass_init = True  # eqx.Module itself
+        has_dataclass_post_init = "__post_init__" in cls.__dict__
 
         # Check for a common error. (Check for `_Initable` to avoid duplicate warnings.)
         if (
             not has_dataclass_init
-            and hasattr(cls, "__post_init__")
+            and has_dataclass_post_init
             and not issubclass(cls, _Initable)
         ):
             warnings.warn(
@@ -284,7 +285,7 @@ def __new__(
 
         # Add support for `eqx.field(converter=...)` when using `__post_init__`.
         # (Scenario (c) above. Scenarios (a) and (b) are handled later.)
-        if has_dataclass_init and hasattr(cls, "__post_init__"):
+        if has_dataclass_init and has_dataclass_post_init:
             post_init = cls.__post_init__
 
             @ft.wraps(post_init)  # pyright: ignore

tests/test_module.py

@@ -1169,3 +1169,39 @@ class InvalidArr(eqx.Module):
         match="A JAX array is being set as static!",
     ):
         InvalidArr((), jnp.ones(10))
+
+
+def test_multiple_inheritance():
+    class A(eqx.Module):
+        def __post_init__(self) -> None:
+            if hasattr(super(), "__post_init__"):
+                super().__post_init__()  # pyright: ignore
+
+    class B(A):
+        x: jax.Array = eqx.field(init=False)
+
+        def __post_init__(self) -> None:
+            super().__post_init__()
+            self.x = jnp.zeros(())
+
+    class C(A):
+        pass
+
+    class D(C, A):
+        def __post_init__(self) -> None:
+            super().__post_init__()
+
+    class E(D, B):
+        pass
+
+    E()
+
+
+def test_init_despite_post_init_in_super():
+    class A(eqx.Module):
+        def __post_init__(self) -> None:
+            pass
+
+    class B(A):
+        def __init__(self) -> None:
+            pass