The let_underscore_drop lint checks for statements which don’t bind
an expression which has a non-trivial Drop implementation to anything,
causing the expression to be dropped immediately instead of at end of
scope.
The let_underscore_drop_guard lint checks for statements which don’t bind
a DropGuard to anything, causing its closure to run immediately instead
of at end of scope, which is typically incorrect.
The let_underscore_lock lint checks for statements which don’t bind
a mutex to anything, causing the lock to be released immediately instead
of at end of scope, which is typically incorrect.