Clang disregards deleted copy constructor

[tomboehmer]

https://godbolt.org/z/e6MPqErrh

#include <concepts>

struct Outcome;

struct Fn {
	Fn(Fn const&) = delete;

	template<typename F>
		requires (not std::same_as<Fn, std::remove_reference_t<F>>)
		     and std::invocable<F>
	Fn(F&& f);

	Outcome operator()() const;
};

struct Work {
	Fn fn;
};

int main() {
}

While declaring the implicit copy constructor for Work clang considers the templated constructor of Fn even though Fn declares a deleted copy constructor.

Using libc++ this becomes apparent evaluating std::invocable<const Fn&> when Outcome is used before it is defined, triggering a compilation error.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[royjacobson]

I think I understand what happens. If I understand correctly the standard, we perform direct-initialization for each member of Work, in this case Fn fn. To perform direct-initialization we have to perform overload resolution for Fn's constructors which checks the constraints of the templated constructor and fails there before we find out that the deleted constructor is a better candidate.

So this looks to me like another case of 'SFINAE should make the concept unsatisfied, not invalid' from #48857

[cor3ntin]

Fixed in trunk https://godbolt.org/z/4815b981W