> do these languages let programmers explicitly assert that a certain, relevant property holds at runtime?
Yes, but the programmer has to do the really, really, really hard work of proving that's the case. Otherwise, the compiler says: you haven't proved to me that it's true, so I won't let you make this assertion. Put another way: the compiler checks your proof, but it doesn't write it for you.
The only programs for which all interesting assertions have been proven in this, or a similar, way have not only been small (up to ~10KLOC), but the size of such programs relative to that of the average program has been falling for several decades.
Yes, but the programmer has to do the really, really, really hard work of proving that's the case. Otherwise, the compiler says: you haven't proved to me that it's true, so I won't let you make this assertion. Put another way: the compiler checks your proof, but it doesn't write it for you.
The only programs for which all interesting assertions have been proven in this, or a similar, way have not only been small (up to ~10KLOC), but the size of such programs relative to that of the average program has been falling for several decades.