fix(deallocate_middle): skip to next in try_insert_after

If the next hole node is still lower than the hole to be added, skip the
list.

For this to trigger, this patch modifies the `deallocate_middle()` test.
It requires two holes in the list before the one to be deallocated.

Signed-off-by: Harald Hoyer <harald@profian.com>

Author: haraldh

src/hole.rs

@@ -435,6 +435,11 @@ impl Cursor {
 
             // If we have a next, does the node overlap next?
             if let Some(next) = self.current().next.as_ref() {
+                if next < &node {
+                    // advance the list more
+                    return Err(());
+                }
+
                 let node_u8 = node_u8 as *const u8;
                 assert!(
                     node_u8.wrapping_add(node_size) <= next.as_ptr().cast::<u8>(),

src/test.rs

@@ -151,9 +151,10 @@ fn deallocate_middle() {
         heap.deallocate(z, layout.clone());
         assert_eq!((*(x.as_ptr() as *const Hole)).size, size);
         assert_eq!((*(z.as_ptr() as *const Hole)).size, size);
-        heap.deallocate(y, layout.clone());
-        assert_eq!((*(x.as_ptr() as *const Hole)).size, size * 3);
         heap.deallocate(a, layout.clone());
+        assert_eq!((*(x.as_ptr() as *const Hole)).size, size);
+        assert_eq!((*(z.as_ptr() as *const Hole)).size, heap.size - 2 * size);
+        heap.deallocate(y, layout.clone());
         assert_eq!((*(x.as_ptr() as *const Hole)).size, heap.size);
     }
 }