From c9a56ac21bd830304df990d8d9667cd7e3b53f90 Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Tue, 25 Jul 2023 16:15:39 -0700
Subject: [PATCH] Equivalent of
 https://github.com/google/clif/commit/5718e4d0807fd3b6a8187dde140069120b81ecef

---
 tests/CMakeLists.txt                       |  1 +
 tests/test_python_multiple_inheritance.cpp | 45 ++++++++++++++++++++++
 tests/test_python_multiple_inheritance.py  | 39 +++++++++++++++++++
 3 files changed, 85 insertions(+)
 create mode 100644 tests/test_python_multiple_inheritance.cpp
 create mode 100644 tests/test_python_multiple_inheritance.py

diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 80ee9c1f1..d68067df6 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -144,6 +144,7 @@ set(PYBIND11_TEST_FILES
     test_opaque_types
     test_operator_overloading
     test_pickling
+    test_python_multiple_inheritance
     test_pytypes
     test_sequences_and_iterators
     test_smart_ptr
diff --git a/tests/test_python_multiple_inheritance.cpp b/tests/test_python_multiple_inheritance.cpp
new file mode 100644
index 000000000..e3a66fb84
--- /dev/null
+++ b/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 {
+    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 {
+    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);
+}
diff --git a/tests/test_python_multiple_inheritance.py b/tests/test_python_multiple_inheritance.py
new file mode 100644
index 000000000..57c196030
--- /dev/null
+++ b/tests/test_python_multiple_inheritance.py
@@ -0,0 +1,39 @@
+# 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 PPCCInit(PC, m.CppDrvd):
+    def __init__(self, value):
+        PC.__init__(self, value)
+        m.CppDrvd.__init__(self, value + 1)
+
+
+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_PPCCInit():
+    d = PPCCInit(11)
+    assert d.get_drvd_value() == 36
+    d.reset_drvd_value(55)
+    assert d.get_drvd_value() == 55
+
+    # CppBase is initialized and used when CppBase methods are called, but
+    # CppDrvd is used when CppDrvd methods are called.
+    assert d.get_base_value() == 11
+    assert d.get_base_value_from_drvd() == 12
+    d.reset_base_value(20)
+    assert d.get_base_value() == 20
+    assert d.get_base_value_from_drvd() == 12
+    d.reset_base_value_from_drvd(30)
+    assert d.get_base_value() == 20
+    assert d.get_base_value_from_drvd() == 30