From d4fc392ebe4f8e59d42831ae3a78b4d8d90b0bbd Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Wed, 3 Jul 2024 14:37:39 -0700
Subject: [PATCH] `move_only_holder_caster<type, std::unique_ptr<T, D>>`:
 inherit from `type_caster_base<T>`

CRUDE INTERMEDIATE STATE, just to see if this builds on all platforms.
---
 include/pybind11/cast.h       | 48 +++++++++++++++++++++++++++++++----
 tests/test_class_sh_basic.cpp |  2 +-
 2 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index 0aa75929e..58a606463 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -855,14 +855,14 @@ public:
 
     explicit operator type *() {
         if (typeinfo->default_holder) {
-            throw std::runtime_error("BAKEIN_WIP: operator type *()");
+            throw std::runtime_error("BAKEIN_WIP: operator type *() shared_ptr");
         }
         return this->value;
     }
 
     explicit operator type &() {
         if (typeinfo->default_holder) {
-            throw std::runtime_error("BAKEIN_WIP: operator type &()");
+            throw std::runtime_error("BAKEIN_WIP: operator type &() shared_ptr");
         }
         // static_cast works around compiler error with MSVC 17 and CUDA 10.2
         // see issue #2180
@@ -971,16 +971,54 @@ struct move_only_holder_caster {
 
 // BAKEIN_WIP
 template <typename type, typename deleter>
-struct move_only_holder_caster<type, std::unique_ptr<type, deleter>> {
-    static_assert(std::is_base_of<type_caster_base<type>, type_caster<type>>::value,
+struct move_only_holder_caster<type, std::unique_ptr<type, deleter>>
+    : public type_caster_base<type> {
+public:
+    using base = type_caster_base<type>;
+    static_assert(std::is_base_of<base, type_caster<type>>::value,
                   "Holder classes are only supported for custom types");
+    using base::base;
+    using base::cast;
+    using base::typeinfo;
+    using base::value;
 
     static handle
     cast(std::unique_ptr<type, deleter> &&src, return_value_policy policy, handle parent) {
         return smart_holder_type_caster_support::unique_ptr_to_python(
             std::move(src), policy, parent);
     }
-    static constexpr auto name = type_caster_base<type>::name;
+
+    bool load(handle src, bool convert) {
+        return base::template load_impl<
+            move_only_holder_caster<type, std::unique_ptr<type, deleter>>>(src, convert);
+    }
+
+    bool load_value(value_and_holder &&v_h) {
+        if (typeinfo->default_holder) {
+            sh_load_helper.loaded_v_h = v_h;
+            return true;
+        }
+        return false; // BAKEIN_WIP: What is the best behavior here?
+    }
+
+    explicit operator type *() {
+        throw std::runtime_error("BAKEIN_WIP: operator type *() unique_ptr");
+    }
+
+    explicit operator type &() {
+        throw std::runtime_error("BAKEIN_WIP: operator type &() unique_ptr");
+    }
+
+    template <typename>
+    using cast_op_type = std::unique_ptr<type, deleter>;
+
+    explicit operator std::unique_ptr<type, deleter>() {
+        throw std::runtime_error("WIP operator std::unique_ptr<type, deleter> ()");
+    }
+
+    static bool try_direct_conversions(handle) { return false; }
+
+    smart_holder_type_caster_support::load_helper<remove_cv_t<type>> sh_load_helper; // Const2Mutbl
 };
 
 template <typename type, typename deleter>
diff --git a/tests/test_class_sh_basic.cpp b/tests/test_class_sh_basic.cpp
index 53b7a0f43..030dc2cf7 100644
--- a/tests/test_class_sh_basic.cpp
+++ b/tests/test_class_sh_basic.cpp
@@ -175,7 +175,7 @@ TEST_SUBMODULE(class_sh_basic, m) {
     m.def("rtrn_uqmp", rtrn_uqmp);
     m.def("rtrn_uqcp", rtrn_uqcp);
 
-    // BAKEIN_BREAK m.def("pass_uqmp", pass_uqmp);
+    m.def("pass_uqmp", pass_uqmp);
     // BAKEIN_BREAK m.def("pass_uqcp", pass_uqcp);
 
     m.def("rtrn_udmp", rtrn_udmp);