Rollup merge of #76983 - ssomers:btree_extra_test, r=Mark-Simulacrum

BTreeMap: extra testing & fixed comments

r? @Mark-Simulacrum

Author: RalfJung

library/alloc/src/collections/btree/map/tests.rs

@@ -88,6 +88,11 @@ impl<'a, K: 'a, V: 'a> BTreeMap<K, V> {
                     let min_len = if is_root { 1 } else { node::MIN_LEN };
                     assert!(node.len() >= min_len, "{} < {}", node.len(), min_len);
 
+                    for idx in 0..=node.len() {
+                        let edge = unsafe { node::Handle::new_edge(node, idx) };
+                        assert!(edge.descend().ascend().ok().unwrap() == edge);
+                    }
+
                     internal_length += node.len();
                 }
                 Position::InternalKV(kv) => {
@@ -1846,3 +1851,17 @@ fn test_into_values() {
     assert!(values.contains(&'b'));
     assert!(values.contains(&'c'));
 }
+
+#[test]
+fn test_insert_remove_intertwined() {
+    let loops = if cfg!(miri) { 100 } else { 1_000_000 };
+    let mut map = BTreeMap::new();
+    let mut i = 1;
+    for _ in 0..loops {
+        i = (i + 421) & 0xFF;
+        map.insert(i, i);
+        map.remove(&(0xFF - i));
+    }
+
+    map.check();
+}

library/alloc/src/collections/btree/node.rs

@@ -613,8 +613,8 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
 }
 
 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
-    /// Adds a key/value pair and an edge to go to the right of that pair to
-    /// the end of the node.
+    /// Adds a key/value pair, and an edge to go to the right of that pair,
+    /// to the end of the node.
     pub fn push(&mut self, key: K, val: V, edge: Root<K, V>) {
         assert!(edge.height == self.height - 1);
 
@@ -630,8 +630,8 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
         }
     }
 
-    /// Adds a key/value pair and an edge to go to the left of that pair to
-    /// the beginning of the node.
+    /// Adds a key/value pair, and an edge to go to the left of that pair,
+    /// to the beginning of the node.
     pub fn push_front(&mut self, key: K, val: V, edge: Root<K, V>) {
         assert!(edge.height == self.height - 1);
         assert!(self.len() < CAPACITY);
@@ -1152,7 +1152,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
     ///
     /// - The node is truncated to only contain the key/value pairs to the right of
     ///   this handle.
-    /// - The key and value pointed to by this handle and extracted.
+    /// - The key and value pointed to by this handle are extracted.
     /// - All the key/value pairs to the right of this handle are put into a newly
     ///   allocated node.
     pub fn split(mut self) -> (NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, K, V, Root<K, V>) {
@@ -1196,7 +1196,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
     ///
     /// - The node is truncated to only contain the edges and key/value pairs to the
     ///   right of this handle.
-    /// - The key and value pointed to by this handle and extracted.
+    /// - The key and value pointed to by this handle are extracted.
     /// - All the edges and key/value pairs to the right of this handle are put into
     ///   a newly allocated node.
     pub fn split(mut self) -> (NodeRef<marker::Mut<'a>, K, V, marker::Internal>, K, V, Root<K, V>) {