Part of the kernel crate, a ScopeGuard is a wrapper around a function pointer which calls said function whenever the ScopeGuard instance stops being referenced.

It's useful for example to handle cleanups when a function has more complicated cleanup than just freeing memory or unlocking locks.
The user can call disarm on the ScopeGuard instance to prevent it from firing:

// Create an anonymous function to perform cleanup
let guard = ScopeGuard::new(|| {
  ... // Cleanup code
});

// --snip--

if some_condition() {
  return; // guard goes out of scope, runs cleanup code
}

// --snip--

// When the function exits normally, the guard can be disarmed
guard.disarm();
return;

It's similar to defer in other languages, with the addition of being able to skip the defer closure execution if needed.

There's also a standalone scopeguard crate which accomplishes a similar behavior.

Source:

• [1] https://lwn.net/Articles/990489/