I'm experimentally rebuilding rawhide with the not-yet-released GCC 15 to see if anything breaks, and to help write the porting guide.  See https://fedoraproject.org/wiki/User:Dmalcolm/gcc-15

My test build with GCC 15 failed:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed/build/8476032/

whereas my test build with GCC 14 succeeded:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed.checker/build/8477581/

The failing build failed with:

In file included from ../../Sources/API/signals.h:52,
                 from ../../Sources/Core/precomp.h:46,
                 from core_iostream.cpp:30:
../../Sources/API/Signals/signal_v3.h: In copy constructor ‘CL_Signal_v3<PARAM1, PARAM2, PARAM3>::CL_Signal_v3(const CL_Signal_v3<PARAM1, PARAM2, PARAM3>&)’:
../../Sources/API/Signals/signal_v3.h:93:52: error: ‘class CL_Signal_v3<PARAM1, PARAM2, PARAM3>’ has no member named ‘owner’ [-Wtemplate-body]
   93 |                         slot->add_signal_ref(this->owner);
      |                                                    ^~~~~
In file included from ../../Sources/API/signals.h:52,
                 from ../../Sources/Core/precomp.h:46,
                 from precomp.cpp:30:
../../Sources/API/Signals/signal_v3.h: In copy constructor ‘CL_Signal_v3<PARAM1, PARAM2, PARAM3>::CL_Signal_v3(const CL_Signal_v3<PARAM1, PARAM2, PARAM3>&)’:
../../Sources/API/Signals/signal_v3.h:93:52: error: ‘class CL_Signal_v3<PARAM1, PARAM2, PARAM3>’ has no member named ‘owner’ [-Wtemplate-body]
   93 |                         slot->add_signal_ref(this->owner);
      |                                                    ^~~~~

which FWIW doesn't match any of the other failures I've seen with GCC 15.

Reproducible: Always