Fix elements exceeding node size for unrolled lists

[dmun]

On coalesce, the left and right nodes' locations and pointers are swapped, but not size, meaning that a node could have 6 elements but have size 4.

If you append this resulting node to an empty list, they don't coalesce and an empty node would remain as the head, while still linking to the other node, causing what you see below:

Before

(define (foo x)
  (append '() (reverse (range 0 x))))

;; 5 to 8 fail
(foo 4) ; => '(3 2 1 0)
(foo 5) ; => '()
(foo 6) ; => '()
(foo 7) ; => '()
(foo 8) ; => '()
(foo 9) ; => '(8 7 6 5 4 3 2 1 0)

;; contradicting length and empty?
(length (foo 6)) ; => 6
(empty? (foo 6)) ; => #true

type SmallRcList<T> = UnrolledList<T, RcPointer, 4, 2>;
let left: SmallRcList<i32> = SmallRcList::new();
let right: SmallRcList<_> = (0..6).collect::<SmallRcList<_>>().reverse();
let left = left.append(right);

left.node_iter().for_each(|node| {
    println!("{}/{}: {:?}", node.index(), node.size(), node.elements());
});

// Output:
// 0/4: []
// 6/4: [0, 1, 2, 3, 4, 5]

After

After adding the size swap + test

(foo 4) ; => '(3 2 1 0)
(foo 5) ; => '(4 3 2 1 0)
(foo 6) ; => '(5 4 3 2 1 0)
(foo 7) ; => '(6 5 4 3 2 1 0)
(foo 8) ; => '(7 6 5 4 3 2 1 0)
(foo 9) ; => '(8 7 6 5 4 3 2 1 0)

(length (foo 6)) ; => 6
(empty? (foo 6)) ; => #false

// same rust code

// Output:
// 6/8: [0, 1, 2, 3, 4, 5]

Notes

Also, seems like asserts_invariants() didn't call assert!, when I added it, more errors appeared. All seem fixed after my change.

failures:
    unrolled::iterator_tests::empty_node_appending_coalescing_works
    unrolled::proptests::vlist::append_non_mut_resulting_length_equivalent
    unrolled::proptests::vlist::append_resulting_length_equivalent
    unrolled::proptests::vlist::append_zero_then_popfront
    unrolled::proptests::vlist::operations_in_order_match
    unrolled::proptests::vlist::test_case_with_pop_front
    unrolled::proptests::vlist::test_case_with_reverse
    unrolled::proptests::vlist_growth_rate_4::append_non_mut_resulting_length_equivalent
    unrolled::proptests::vlist_growth_rate_4::append_resulting_length_equivalent
    unrolled::proptests::vlist_growth_rate_4::cdr_to_append
    unrolled::proptests::vlist_growth_rate_4::larger_test_case
    unrolled::proptests::vlist_growth_rate_4::operations_in_order_match
    unrolled::proptests::vlist_growth_rate_4::test_case_with_pop_front
    unrolled::proptests::vlist_growth_rate_4::test_case_with_reverse

test result: FAILED. 210 passed; 14 failed; 0 ignored; 0 measured; 0 filtered out; finished in 2.25s

test result: ok. 224 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 2.51s

[mattwparas]

Good catch, thank you! I'll publish a new release tonight