fix: catch missing self argument in overloads constructor (#2914)

Author: rhaschke

include/pybind11/pybind11.h

@@ -555,8 +555,8 @@ class cpp_function : public function {
 
         auto self_value_and_holder = value_and_holder();
         if (overloads->is_constructor) {
-            if (!PyObject_TypeCheck(parent.ptr(), (PyTypeObject *) overloads->scope.ptr())) {
-                PyErr_SetString(PyExc_TypeError, "__init__(self, ...) called with invalid `self` argument");
+            if (!parent || !PyObject_TypeCheck(parent.ptr(), (PyTypeObject *) overloads->scope.ptr())) {
+                PyErr_SetString(PyExc_TypeError, "__init__(self, ...) called with invalid or missing `self` argument");
                 return nullptr;
             }
 

tests/test_factory_constructors.py

@@ -486,7 +486,9 @@ def __init__(self, bad):
     # Same as above, but for a class with an alias:
     class BrokenTF6(m.TestFactory6):
         def __init__(self, bad):
-            if bad == 1:
+            if bad == 0:
+                m.TestFactory6.__init__()
+            elif bad == 1:
                 a = m.TestFactory2(tag.pointer, 1)
                 m.TestFactory6.__init__(a, tag.base, 1)
             elif bad == 2:
@@ -506,13 +508,13 @@ def __init__(self, bad):
             BrokenTF1(arg)
         assert (
             str(excinfo.value)
-            == "__init__(self, ...) called with invalid `self` argument"
+            == "__init__(self, ...) called with invalid or missing `self` argument"
         )
 
-    for arg in (1, 2, 3, 4):
+    for arg in (0, 1, 2, 3, 4):
         with pytest.raises(TypeError) as excinfo:
             BrokenTF6(arg)
         assert (
             str(excinfo.value)
-            == "__init__(self, ...) called with invalid `self` argument"
+            == "__init__(self, ...) called with invalid or missing `self` argument"
         )