First, the language can't save you from getting the program semantics wrong (e.g. if you never delete an entry from a hashmap even after you're done with it, you're leaking that memory). No language can save you from leaks as a general concept.
Second, Rust makes a very specific promise — freedom from data races. Leaking resources does not actually break that promise, because it doesn't allow you to access that resource any more.
First, the language can't save you from getting the program semantics wrong (e.g. if you never delete an entry from a hashmap even after you're done with it, you're leaking that memory). No language can save you from leaks as a general concept.
Second, Rust makes a very specific promise — freedom from data races. Leaking resources does not actually break that promise, because it doesn't allow you to access that resource any more.