Rust's memory safety guarantees do not insure the absence of leaks. However, Rust's design does offer significant protection against leaks (relative to languages like C where all heap allocations must be explicitly freed).
The fact that any felt it nessasary to add a "leak" function to the standard library should tell you something about how easy it is to accidentally leak memory.
The fact that any felt it nessasary to add a "leak" function to the standard library should tell you something about how easy it is to accidentally leak memory.