From 17c0354050ad377eef38cbe57453e24a79989c3f Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Wed, 3 Jul 2024 10:30:14 -0700
Subject: [PATCH] `copyable_holder_caster<type, std::shared_ptr<type>>`: split
 `load_value_shared_ptr()`, `load_value_smart_holder()` (the latter just
 throws right now)

---
 include/pybind11/cast.h | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index aca6ce8b1..34d7178a3 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -867,13 +867,9 @@ public:
 
 protected:
     friend class type_caster_generic;
-    void check_holder_compat() {
-        if (typeinfo->default_holder) {
-            throw cast_error("Unable to load a custom holder type from a default-holder instance");
-        }
-    }
+    void check_holder_compat() {}
 
-    bool load_value(value_and_holder &&v_h) {
+    bool load_value_shared_ptr(value_and_holder &&v_h) {
         if (v_h.holder_constructed()) {
             value = v_h.value_ptr();
             holder = v_h.template holder<std::shared_ptr<type>>();
@@ -889,6 +885,17 @@ protected:
 #endif
     }
 
+    bool load_value_smart_holder(value_and_holder && /*v_h*/) {
+        throw std::runtime_error("BAKEIN_WIP load_value_smart_holder");
+    }
+
+    bool load_value(value_and_holder &&v_h) {
+        if (typeinfo->default_holder) {
+            return load_value_smart_holder(std::move(v_h));
+        }
+        return load_value_shared_ptr(std::move(v_h));
+    }
+
     template <typename T = std::shared_ptr<type>,
               detail::enable_if_t<!std::is_constructible<T, const T &, type *>::value, int> = 0>
     bool try_implicit_casts(handle, bool) {