Double-free in id-map

The clone_from implementation for IdMap drops the values present in the map and then begins cloning values from the other map. If a .clone() call pancics, then the afformentioned dropped elements can be freed again.
get_or_insert

get_or_insert reserves space for a value, before calling the user provided insertion function f. If the function f panics then uninitialized or previously freed memory can be dropped.
remove_set

When removing a set of elements, ptr::drop_in_place is called on each of the element to be removed. If the Drop impl of one of these elements panics then the previously dropped elements can be dropped again.