Fix and test for issue #4117

include/pybind11/cast.h

@@ -1178,11 +1178,13 @@ template <typename T>
 enable_if_t<cast_is_temporary_value_reference<T>::value, T> cast_safe(object &&) {
     pybind11_fail("Internal error: cast_safe fallback invoked");
 }
+
 template <typename T>
-enable_if_t<std::is_same<void, intrinsic_t<T>>::value, void> cast_safe(object &&) {}
+enable_if_t<std::is_same<void, remove_cvref_t<T>>::value, void> cast_safe(object &&) {}
+
 template <typename T>
 enable_if_t<detail::none_of<cast_is_temporary_value_reference<T>,
-                            std::is_same<void, intrinsic_t<T>>>::value,
+                            std::is_same<void, remove_cvref_t<T>>>::value,
             T>
 cast_safe(object &&o) {
     return pybind11::cast<T>(std::move(o));

tests/test_virtual_functions.cpp

@@ -230,6 +230,35 @@ inline int test_override_cache(std::shared_ptr<test_override_cache_helper> const
 // are rather long).
 void initialize_inherited_virtuals(py::module_ &m);
 
+namespace issue_4117 { // Broken by PR #3861
+
+class Animal {
+public:
+    virtual ~Animal() {}
+    virtual void *go() = 0;
+};
+
+class PyAnimal : public Animal {
+public:
+    /* Inherit the constructors */
+    using Animal::Animal;
+    /* Trampoline (need one for each virtual function) */
+    void *go() override {
+        PYBIND11_OVERRIDE_PURE(void *, /* Return type */
+                               Animal, /* Parent class */
+                               go,     /* Name of function in C++ (must match Python name) */
+        );
+    }
+};
+
+void bindings(py::module_ m) {
+    py::class_<Animal, PyAnimal /* <--- trampoline*/>(m, "Issue4117Animal")
+        .def(py::init<>())
+        .def("go", &Animal::go);
+}
+
+} // namespace issue_4117
+
 TEST_SUBMODULE(virtual_functions, m) {
     // test_override
     py::class_<ExampleVirt, PyExampleVirt>(m, "ExampleVirt")
@@ -410,6 +439,8 @@ TEST_SUBMODULE(virtual_functions, m) {
         .def("func", &test_override_cache_helper::func);
 
     m.def("test_override_cache", test_override_cache);
+
+    issue_4117::bindings(m);
 }
 
 // Inheriting virtual methods.  We do two versions here: the repeat-everything version and the

tests/test_virtual_functions.py

@@ -457,3 +457,12 @@ class Test(m.test_override_cache_helper):
     for _ in range(1500):
         assert m.test_override_cache(func()) == 42
         assert m.test_override_cache(func2()) == 0
+
+
+def test_issue_4117():
+    class Lynx(m.Issue4117Animal):
+        def go(self):
+            return self
+
+    obj = Lynx()
+    assert obj.go() is obj