Adding classu alias for class_<U, std::unique_ptr<U>>.

include/pybind11/smart_holder.h

@@ -19,4 +19,12 @@ public:
     using class_<type_, smart_holder, options...>::class_;
 };
 
+// Similar in idea to `py::classh`, but for `std::unique_ptr<U>` holder, to support
+// an easier transition to `py::smart_holder` as default holder.
+template <typename type_, typename... options>
+class classu : public class_<type_, std::unique_ptr<type_>, options...> {
+public:
+    using class_<type_, std::unique_ptr<type_>, options...>::class_;
+};
+
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

tests/test_class_sh_unique_ptr_member.cpp

@@ -50,7 +50,8 @@ TEST_SUBMODULE(class_sh_unique_ptr_member, m) {
 
     m.def("make_unique_pointee", make_unique_pointee);
 
-    py::class_<ptr_owner>(m, "ptr_owner")
+    // Could also be class_, but can conveniently be used for testing classu.
+    py::classu<ptr_owner>(m, "ptr_owner")
         .def(py::init<std::unique_ptr<pointee>>(), py::arg("ptr"))
         .def("is_owner", &ptr_owner::is_owner)
         .def("give_up_ownership_via_unique_ptr", &ptr_owner::give_up_ownership_via_unique_ptr)