MutexGuard's Debug implementation is unuseful

[m-ou-se]

MutexGuard's Debug implementation just forwards to the Mutex's Debug implementation, which will simply print <locked>, because the Mutex was locked (by that very same MutexGuard).

Effectively, this means that the current Debug implementation of MutexGuard is equivalent to:

f.write_str("MutexGuard { lock: Mutex { data: <locked> } }")

Instead, it should not try to lock the mutex, but use its own Deref implementation to print the contents of the mutex.