From 6ff547e18a4b2347802db4f4117db8393603daea Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Mon, 1 Jul 2024 12:39:45 -0700
Subject: [PATCH] Introduce type_caster_base<>::unique_ptr_to_python()

---
 include/pybind11/cast.h                    |  3 +--
 include/pybind11/detail/type_caster_base.h | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index 88ad045c7..d19a6c15e 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -932,8 +932,7 @@ struct move_only_holder_caster<type, std::unique_ptr<type, deleter>> {
                   "Holder classes are only supported for custom types");
 
     static handle cast(std::unique_ptr<type, deleter> &&src, return_value_policy, handle) {
-        auto *ptr = src.get();
-        return type_caster_base<type>::cast_holder(ptr, std::addressof(src));
+        return type_caster_base<type>::unique_ptr_to_python(std::move(src));
     }
     static constexpr auto name = type_caster_base<type>::name;
 };
diff --git a/include/pybind11/detail/type_caster_base.h b/include/pybind11/detail/type_caster_base.h
index fd8c81b9a..1630c16fb 100644
--- a/include/pybind11/detail/type_caster_base.h
+++ b/include/pybind11/detail/type_caster_base.h
@@ -1160,6 +1160,22 @@ public:
                                          holder);
     }
 
+    template <typename T, typename D>
+    static handle unique_ptr_to_python(std::unique_ptr<T, D> &&unq_ptr) {
+        auto *src = unq_ptr.get();
+        auto st = src_and_type(src);
+        if (st.second->default_holder) {
+            throw std::runtime_error("BAKEIN_WIP");
+        }
+        return type_caster_generic::cast(st.first,
+                                         return_value_policy::take_ownership,
+                                         {},
+                                         st.second,
+                                         nullptr,
+                                         nullptr,
+                                         std::addressof(unq_ptr));
+    }
+
     template <typename T>
     using cast_op_type = detail::cast_op_type<T>;