I agree. The problem with eager diagnostics and templates is that the program could define a `Base<int>` specialization that has a working copy constructor lat

I agree. The problem with eager diagnostics and templates is that the program could define a `Base<int>` specialization that has a working copy constructor later. [0] I think if you define an explicit instantiation definition, it should type check at that point and error. [1] I find myself sometimes defining explicit instantiations to make clangd useful (can also help avoid repeated instantiations if you use explicit declarations in other TUs). [0] https://en.cppreference.com/w/cpp/language/template_specialization.html https://en.cppreference.com/w/cpp/language/template_speciali... [1] https://en.cppreference.com/w/cpp/language/class_template.html https://en.cppreference.com/w/cpp/language/class_template.ht...