https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110122
--- Comment #5 from waffl3x <waffl3x at protonmail dot com> --- (In reply to Patrick Palka from comment #4) > > Yes, it seems the original testcase is exhibiting two bugs (one of which a > GCC 13 regression), whereas the second testcase exhibits one > (non-regression) bug. > > In your original testcase Bar's copy constructor shouldn't be needed since > the template parameter V isn't being copied anywhere, but we're somehow end > up with an illegitimate use of the constructor (bug #1) and then we're also > failing to synthesize it (bug #2). > > In the second testcase Bar's copy constructor is legitimately needed since > we're arguably making a copy of V when writing the specialization > Doppelganger<V>, but we fail to synthesize the constructor (bug #2). > Ah okay got it, bug #1 is pretty harmless then isn't it, because there should never be a situation where the illegitimate use of the constructor will be an error, it only popped up because bug #2 happened. On the other hand, this makes me wonder about what's going on during class template instantiation, at worst it's probably an inefficiency rather than anything potentially harmful though. > > Ah, does it work for you to give Bar an explicitly defaulted copy and > default ctor? Yes actually, that does seem to do the trick. https://godbolt.org/z/x7eYzY6dz
