//@ When analyzing the code of `rust_foo`, Rust has to assign a lifetime to `first`. It will choose the scope
//@ where `first` is valid, which is the entire rest of the function. Because `head` ties the lifetime of its
//@ argument and return value together, this means that `&v` also has to borrow `v` for the entire duration of
//@ When analyzing the code of `rust_foo`, Rust has to assign a lifetime to `first`. It will choose the scope
//@ where `first` is valid, which is the entire rest of the function. Because `head` ties the lifetime of its
//@ argument and return value together, this means that `&v` also has to borrow `v` for the entire duration of