No, throwing an exception in these situation is still a precondition violation -> undefined behavior. The unconditional "noexcept" just means no exception will escape, but regardless you still need to play by the rules (i.e. satisfy the preconditions).

https://timsong-cpp.github.io/cppwp/n3337/unique.ptr.single.ctor
Looks like std::unique_ptr<T, D>{} has had UB since C++11 for the right D. Even though it could just have been a call to std::terminate.

079f7d3 added noexcept to certain constructors that had the precondition that some initialization didn't throw.

Is that the right commit ID? It didn't add any noexcept.

I agree that making it UB is bad. We should just rely on the compiler to terminate. We should try to reduce the places where programs have unnecessary undefined behaviour.

But I think this needs an lwg issue.

079f7d3 added noexcept to certain constructors that had the precondition that some initialization didn't throw.

Is that the right commit ID? It didn't add any noexcept.

No.

I agree that making it UB is bad. We should just rely on the compiler to terminate. We should try to reduce the places where programs have unnecessary undefined behaviour.

But I think this needs an lwg issue.

Yes. This seems like a low-hanging fruit compared to other sources of library UB. I'll take a look again and submit a LWG issue.