Snapshot of pybind/pybind11#4762 applied to pywrapcc

include/pybind11/cast.h

@@ -1618,7 +1618,13 @@ inline namespace literals {
 /** \rst
     String literal version of `arg`
  \endrst */
-constexpr detail::arg_base operator"" _a(const char *name, size_t) {
+constexpr detail::arg_base
+#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ < 5
+operator"" _a // gcc 4.8.5 insists on having a space (hard error).
+#else
+operator""_a // clang 17 generates a deprecation warning if there is a space.
+#endif
+    (const char *name, size_t) {
     return detail::arg_base(name);
 }
 } // namespace literals

include/pybind11/detail/class.h

@@ -180,6 +180,17 @@ extern "C" inline PyObject *pybind11_meta_getattro(PyObject *obj, PyObject *name
     return PyType_Type.tp_getattro(obj, name);
 }
 
+// Band-aid workaround to fix a subtle but serious bug in a minimalistic fashion. See PR #4762.
+inline bool is_redundant_value_and_holder(const std::vector<type_info *> &bases,
+                                          std::size_t ix_base) {
+    for (std::size_t i = 0; i < ix_base; i++) {
+        if (PyType_IsSubtype(bases[i]->type, bases[ix_base]->type) != 0) {
+            return true;
+        }
+    }
+    return false;
+}
+
 /// metaclass `__call__` function that is used to create all pybind11 objects.
 extern "C" inline PyObject *pybind11_meta_call(PyObject *type, PyObject *args, PyObject *kwargs) {
 
@@ -189,18 +200,20 @@ extern "C" inline PyObject *pybind11_meta_call(PyObject *type, PyObject *args, P
         return nullptr;
     }
 
-    // This must be a pybind11 instance
-    auto *instance = reinterpret_cast<detail::instance *>(self);
-
     // Ensure that the base __init__ function(s) were called
-    for (const auto &vh : values_and_holders(instance)) {
-        if (!vh.holder_constructed()) {
+    const auto &bases = all_type_info((PyTypeObject *) type);
+    values_and_holders vhs(reinterpret_cast<detail::instance *>(self));
+    assert(bases.size() == vhs.size());
+    std::size_t ix_base = 0;
+    for (const auto &vh : vhs) {
+        if (!vh.holder_constructed() && !is_redundant_value_and_holder(bases, ix_base)) {
             PyErr_Format(PyExc_TypeError,
                          "%.200s.__init__() must be called when overriding __init__",
                          get_fully_qualified_tp_name(vh.type->type).c_str());
             Py_DECREF(self);
             return nullptr;
         }
+        ix_base++;
     }
 
     return self;

include/pybind11/detail/type_caster_base.h

@@ -102,8 +102,22 @@ class loader_life_support {
 inline std::pair<decltype(internals::registered_types_py)::iterator, bool>
 all_type_info_get_cache(PyTypeObject *type);
 
+// Band-aid workaround to fix a subtle but serious bug in a minimalistic fashion. See PR #4762.
+inline void all_type_info_add_base_most_derived_first(std::vector<type_info *> &bases,
+                                                      type_info *addl_base) {
+    for (auto it = bases.begin(); it != bases.end(); it++) {
+        type_info *existing_base = *it;
+        if (PyType_IsSubtype(addl_base->type, existing_base->type) != 0) {
+            bases.insert(it, addl_base);
+            return;
+        }
+    }
+    bases.push_back(addl_base);
+}
+
 // Populates a just-created cache entry.
 PYBIND11_NOINLINE void all_type_info_populate(PyTypeObject *t, std::vector<type_info *> &bases) {
+    assert(bases.empty());
     std::vector<PyTypeObject *> check;
     for (handle parent : reinterpret_borrow<tuple>(t->tp_bases)) {
         check.push_back((PyTypeObject *) parent.ptr());
@@ -136,7 +150,7 @@ PYBIND11_NOINLINE void all_type_info_populate(PyTypeObject *t, std::vector<type_
                     }
                 }
                 if (!found) {
-                    bases.push_back(tinfo);
+                    all_type_info_add_base_most_derived_first(bases, tinfo);
                 }
             }
         } else if (type->tp_bases) {

include/pybind11/pytypes.h

@@ -1620,7 +1620,15 @@ inline namespace literals {
 /** \rst
     String literal version of `str`
  \endrst */
-inline str operator"" _s(const char *s, size_t size) { return {s, size}; }
+inline str
+#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ < 5
+operator"" _s // gcc 4.8.5 insists on having a space (hard error).
+#else
+operator""_s // clang 17 generates a deprecation warning if there is a space.
+#endif
+    (const char *s, size_t size) {
+    return {s, size};
+}
 } // namespace literals
 
 /// \addtogroup pytypes

tests/CMakeLists.txt

@@ -166,6 +166,7 @@ set(PYBIND11_TEST_FILES
     test_opaque_types
     test_operator_overloading
     test_pickling
+    test_python_multiple_inheritance
     test_pytypes
     test_return_value_policy_override
     test_return_value_policy_pack

tests/test_python_multiple_inheritance.cpp

@@ -0,0 +1,45 @@
+#include "pybind11_tests.h"
+
+namespace test_python_multiple_inheritance {
+
+// Copied from:
+// https://github.com/google/clif/blob/5718e4d0807fd3b6a8187dde140069120b81ecef/clif/testing/python_multiple_inheritance.h
+
+struct CppBase {
+    explicit CppBase(int value) : base_value(value) {}
+    int get_base_value() const { return base_value; }
+    void reset_base_value(int new_value) { base_value = new_value; }
+
+private:
+    int base_value;
+};
+
+struct CppDrvd : CppBase {
+    explicit CppDrvd(int value) : CppBase(value), drvd_value(value * 3) {}
+    int get_drvd_value() const { return drvd_value; }
+    void reset_drvd_value(int new_value) { drvd_value = new_value; }
+
+    int get_base_value_from_drvd() const { return get_base_value(); }
+    void reset_base_value_from_drvd(int new_value) { reset_base_value(new_value); }
+
+private:
+    int drvd_value;
+};
+
+} // namespace test_python_multiple_inheritance
+
+TEST_SUBMODULE(python_multiple_inheritance, m) {
+    using namespace test_python_multiple_inheritance;
+
+    py::class_<CppBase>(m, "CppBase")
+        .def(py::init<int>())
+        .def("get_base_value", &CppBase::get_base_value)
+        .def("reset_base_value", &CppBase::reset_base_value);
+
+    py::class_<CppDrvd, CppBase>(m, "CppDrvd")
+        .def(py::init<int>())
+        .def("get_drvd_value", &CppDrvd::get_drvd_value)
+        .def("reset_drvd_value", &CppDrvd::reset_drvd_value)
+        .def("get_base_value_from_drvd", &CppDrvd::get_base_value_from_drvd)
+        .def("reset_base_value_from_drvd", &CppDrvd::reset_base_value_from_drvd);
+}

tests/test_python_multiple_inheritance.py

@@ -0,0 +1,35 @@
+# Adapted from:
+# https://github.com/google/clif/blob/5718e4d0807fd3b6a8187dde140069120b81ecef/clif/testing/python/python_multiple_inheritance_test.py
+
+from pybind11_tests import python_multiple_inheritance as m
+
+
+class PC(m.CppBase):
+    pass
+
+
+class PPCC(PC, m.CppDrvd):
+    pass
+
+
+def test_PC():
+    d = PC(11)
+    assert d.get_base_value() == 11
+    d.reset_base_value(13)
+    assert d.get_base_value() == 13
+
+
+def test_PPCC():
+    d = PPCC(11)
+    assert d.get_drvd_value() == 33
+    d.reset_drvd_value(55)
+    assert d.get_drvd_value() == 55
+
+    assert d.get_base_value() == 11
+    assert d.get_base_value_from_drvd() == 11
+    d.reset_base_value(20)
+    assert d.get_base_value() == 20
+    assert d.get_base_value_from_drvd() == 20
+    d.reset_base_value_from_drvd(30)
+    assert d.get_base_value() == 30
+    assert d.get_base_value_from_drvd() == 30