2 Checks whether variables used within while loop condition
3 can be (and are) mutated in the body.
6 If the condition is unchanged, entering the body of the loop
7 will lead to an infinite loop.
10 If the `while`-loop is in a closure, the check for mutation of the
11 condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
12 in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
18 println!("let me loop forever!");