LinkedList leaks Node memory when dropped about rust

[siriak]

@imp2002 could you verify if this is the case, please?

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[imp2002]

@Kylebrown9
Hello, why NonNull never dropped? Impl LinkedList in rust-lang doc with NonNull too. Can you explain where is wrong? I checked, but not found. Thanks.

[esoterra]

The LinkedList in the docs you referenced provides a Drop implementation (line 993) that performs the required freeing. Dropping NonNull itself does not free the referenced memory.

[imp2002]

Use Box::from_raw() free the referenced memory. After calling this function, the raw pointer is owned by the resulting Box. Specifically, the Box destructor will call the destructor of Node<T> and free the allocated memory.

fn pop_back_node(&mut self) -> Option<Box<Node<T>>> {
        self.tail.map(|node| unsafe {
            let node = Box::from_raw(node.as_ptr());
            self.tail = node.prev;

            match self.tail {
                None => self.head = None,
                Some(tail) => (*tail.as_ptr()).next = None,
            }

            self.len -= 1;
            node
        })
    }

[esoterra]

Something like that could work.

Until Drop is implemented for LinkedList such that all nodes are freed, LinkedList will leaks node memory when dropped.
The drop implementation could use Box::from_raw(...) as you say or ptr::drop_in_place(...).

This is a big issue with the example and should be fixed ASAP to avoid misleading readers on the use of NonNull.