Throw TypeError when subclasses forget to call __init__

- Based on pybind/pybind11#2152
- Fixes #1210

Author: virtuald

src/nb_type.cpp

@@ -1032,6 +1032,14 @@ static PyObject *nb_type_vectorcall(PyObject *self, PyObject *const *args_in,
             return nullptr;
         }
 
+        if (((nb_inst *)self)->state == nb_inst::state_uninitialized) {
+            PyErr_Format(PyExc_TypeError,
+                        "%.200s.__init__() must be called when overriding __init__",
+                        td->name);
+            Py_DECREF(self);
+            return nullptr;
+        }
+
         // __init__ constructor: 'rv' is None
         Py_DECREF(rv);
         return self;

tests/test_classes.py

@@ -256,13 +256,9 @@ def name(self):
         def what(self):
             return "b"
 
-    with pytest.warns(
-        RuntimeWarning,
-        match="nanobind: attempted to access an uninitialized instance of type",
-    ):
-        with pytest.raises(TypeError) as excinfo:
-            t.go(Incomplete2())
-    assert "incompatible function arguments" in str(excinfo.value)
+    with pytest.raises(TypeError) as excinfo:
+        Incomplete2()
+    assert "__init__() must be called when overriding __init__" in str(excinfo.value)
 
 
 def test12_large_pointers():