When seastar/core/shared_ptr_incomplete.hh is included in a header
then it causes problems with all declarations of shared_ptr<T> with
incomplete type T that end up in the same compilation unit.
The problem happens when we have a compilation unit that includes
two headers a.hh and b.hh such that a.hh includes
seastar/core/shared_ptr_incomplete.hh and b.hh declares
shared_ptr<T> with incomplete type T. On the same time this
compilation unit does not use declared shared_ptr<T> so it should
compile and work but it does not because shared_ptr_incomplete.hh
is included and it forces instantiation of:
template <typename T>
T*
lw_shared_ptr_accessors<T,
void_t<decltype(lw_shared_ptr_deleter<T>{})>>::to_value(lw_shared_ptr_counter_base*
counter) {
return static_cast<T*>(counter);
}
for each declared shared_ptr<T> with incomplete type T. Even the once
that are never used.
Following commit "Decouple database.hh from types/user.hh"
moves user_types_metadata type out of database.hh and instead
declares shared_ptr<user_types_metadata> in database.hh where
user_types_metadata is incomplete. Without this commit
the compilation of the following one fails with:
In file included from ./sstables/sstables.hh:34,
from ./db/size_estimates_virtual_reader.hh:38,
from db/system_keyspace.cc:77:
seastar/include/seastar/core/shared_ptr_incomplete.hh: In
instantiation of ‘static T*
seastar::internal::lw_shared_ptr_accessors<T,
seastar::internal::void_t<decltype
(seastar::lw_shared_ptr_deleter<T>{})>
>::to_value(seastar::lw_shared_ptr_counter_base*) [with T =
user_types_metadata]’:
seastar/include/seastar/core/shared_ptr.hh:243:51: required from
‘static void seastar::internal::lw_shared_ptr_accessors<T,
seastar::internal::void_t<decltype
(seastar::lw_shared_ptr_deleter<T>{})>
>::dispose(seastar::lw_shared_ptr_counter_base*) [with T =
user_types_metadata]’
seastar/include/seastar/core/shared_ptr.hh:300:31: required from
‘seastar::lw_shared_ptr<T>::~lw_shared_ptr() [with T =
user_types_metadata]’
./database.hh:1004:7: required from ‘static void
seastar::internal::lw_shared_ptr_accessors_no_esft<T>::dispose(seastar::lw_shared_ptr_counter_base*)
[with T = keyspace_metadata]’
seastar/include/seastar/core/shared_ptr.hh:300:31: required from
‘seastar::lw_shared_ptr<T>::~lw_shared_ptr() [with T =
keyspace_metadata]’
./db/size_estimates_virtual_reader.hh:233:67: required from here
seastar/include/seastar/core/shared_ptr_incomplete.hh:38:12: error:
invalid static_cast from type ‘seastar::lw_shared_ptr_counter_base*’
to type ‘user_types_metadata*’
return static_cast<T*>(counter);
^~~~~~~~~~~~~~~~~~~~~~~~
[131/415] CXX build/release/distributed_loader.o
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
316be5c6b5