https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96926
--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> --- So, for the second example, the compiler's process is test() initializes the tuple member looks for tuple(Test) ctor considers tuple(tuple&&) looks for conversion from Test to tuple considers _ImplicitCtor instantiates __is_implicitly_constructible instantiates is_constructible<DependsOnT<Test>, const DependsOnT<Test>&> considers DependsOnT(Test&) tries to convert to Test lazily declares Test copy ctor looks for tuple(tuple) ctor considers _ExplicitCtor instantiates __is_explicitly_constructible instantiates is_constructible<DependsOnT<Test>, const DependsOnT<Test>&> fails So, another problem with trying unsuitable candidates when declaring a copy constructor. I wonder what rule other compilers are using to break this recursive dependency. I'm going to try something that zygoloid suggested GCC already did: if we see a non-template perfect match, don't consider any templates.
