Ah, thanks for the historical take. I learned Rust recently. I like it. I never fought the borrow checker. I was sometimes happily protected by the borrow checker. I never understood what people were talking about.

Right, in early Rust, years ago, it's not even legal to do this:

    fn main() {
        let mut x = 5;
        let y = &x;
        let z = &mut x;
    }

But today's borrowck just goes duh, the reference y goes away right before the variable z is created and everything is cool.

These are called "Non-lexical lifetimes" because the lifetime is no longer strictly tied to a lexical scope - the curly braces in the program - but can have any necessary extent to make things correct.

Further improving the ability of the borrowck to see that what you're doing is fine is an ongoing piece of work for Rust and always will be†, but NLL was the lowest hanging fruit, most of the software I write would need tweaks to account for a strict lexical lifetime and it'd be very annoying when I know I am correct.

† Rice's theorem tells us we can either have a compiler where sometimes illegal borrows are allowed or a compiler where sometimes borrows that should be legal are forbidden (or both, which seems useless), but we cannot have one which is always right, so, Rust chooses the safe option and that means we're always going to be working to make it just a bit better.