While partially using annotations only allows you to eliminate /instances/ of bugs, if you completely apply the annotations then it can allow you to eliminate the entire class of bugs (theoretically). Consider nullabiliy in java.
> I don't see that all of the great masses of Cpp code and libraries would be rewritten or annotated to use these new features.
It's much more likely and tractable that C++ libraries will be annotated than that they'll be rewritten from scratch in Rust.
> I don't see that all of the great masses of Cpp code and libraries would be rewritten or annotated to use these new features.
It's much more likely and tractable that C++ libraries will be annotated than that they'll be rewritten from scratch in Rust.