Revert "Experiment: effectively undoing all shared_from_this modifications."

This reverts commit d72d54e.

Author: rwgk

include/pybind11/detail/smart_holder_type_casters.h

@@ -26,11 +26,6 @@
 #include <typeinfo>
 #include <utility>
 
-#ifdef JUNK
-#    include <iostream>
-inline void to_cout(std::string msg) { std::cout << msg << std::endl; }
-#endif
-
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 using pybindit::memory::smart_holder;
@@ -278,7 +273,6 @@ struct smart_holder_type_caster_class_hooks : smart_holder_type_caster_base_tag
         return false;
     }
 
-#ifdef JUNK
     template <typename WrappedType, typename AnyBaseOfWrappedType>
     static bool try_initialization_using_shared_from_this(
         holder_type *uninitialized_location,
@@ -292,7 +286,6 @@ struct smart_holder_type_caster_class_hooks : smart_holder_type_caster_base_tag
         new (uninitialized_location) holder_type(holder_type::from_shared_ptr(shd_ptr));
         return true;
     }
-#endif
 
     template <typename WrappedType, typename AliasType>
     static void init_instance_for_type(detail::instance *inst, const void *holder_const_void_ptr) {
@@ -305,26 +298,26 @@ struct smart_holder_type_caster_class_hooks : smart_holder_type_caster_base_tag
             register_instance(inst, v_h.value_ptr(), v_h.type);
             v_h.set_instance_registered();
         }
+        auto uninitialized_location = std::addressof(v_h.holder<holder_type>());
+        auto value_ptr_w_t          = v_h.value_ptr<WrappedType>();
         if (holder_void_ptr) {
             // Note: inst->owned ignored.
             auto holder_ptr = static_cast<holder_type *>(holder_void_ptr);
-            new (std::addressof(v_h.holder<holder_type>())) holder_type(std::move(*holder_ptr));
+            new (uninitialized_location) holder_type(std::move(*holder_ptr));
         } else {
             if (!try_initialization_using_shared_from_this(
-                    std::addressof(v_h.holder<holder_type>()),
-                    v_h.value_ptr<WrappedType>(),
-                    v_h.value_ptr<WrappedType>())) {
+                    uninitialized_location, value_ptr_w_t, value_ptr_w_t)) {
                 if (inst->owned) {
-                    new (std::addressof(v_h.holder<holder_type>())) holder_type(
-                        holder_type::from_raw_ptr_take_ownership(v_h.value_ptr<WrappedType>()));
+                    new (uninitialized_location)
+                        holder_type(holder_type::from_raw_ptr_take_ownership(value_ptr_w_t));
                 } else {
-                    new (std::addressof(v_h.holder<holder_type>())) holder_type(
-                        holder_type::from_raw_ptr_unowned(v_h.value_ptr<WrappedType>()));
+                    new (uninitialized_location)
+                        holder_type(holder_type::from_raw_ptr_unowned(value_ptr_w_t));
                 }
             }
         }
         v_h.holder<holder_type>().pointee_depends_on_holder_owner
-            = dynamic_raw_ptr_cast_if_possible<AliasType>(v_h.value_ptr<WrappedType>()) != nullptr;
+            = dynamic_raw_ptr_cast_if_possible<AliasType>(value_ptr_w_t) != nullptr;
         v_h.set_holder_constructed();
     }
 
@@ -394,20 +387,14 @@ struct smart_holder_type_caster_load {
         auto type_raw_ptr = convert_type(void_raw_ptr);
         if (holder().pointee_depends_on_holder_owner) {
             // Tie lifetime of trampoline Python part to C++ part (PR #2839).
-#ifdef JUNK
-            to_cout("");
-            to_cout("LOOOK " + std::to_string(__LINE__) + " " + __FILE__);
-#endif
             return std::shared_ptr<T>(
                 type_raw_ptr,
                 shared_ptr_dec_ref_deleter{
                     handle((PyObject *) load_impl.loaded_v_h.inst).inc_ref()});
         }
-#ifdef JUNK
         if (holder().vptr_is_using_noop_deleter) {
             throw std::runtime_error("Non-owning holder (loaded_as_shared_ptr).");
         }
-#endif
         std::shared_ptr<void> void_shd_ptr = holder().template as_shared_ptr<void>();
         return std::shared_ptr<T>(void_shd_ptr, type_raw_ptr);
     }