3 files changed, 23 insertions, 8 deletions
diff --git a/library/alloc/src/collections/btree/dedup_sorted_iter.rs b/library/alloc/src/collections/btree/dedup_sorted_iter.rs
index 60bf83b83..17ee78045 100644
--- a/library/alloc/src/collections/btree/dedup_sorted_iter.rs
+++ b/library/alloc/src/collections/btree/dedup_sorted_iter.rs
@@ -3,7 +3,9 @@ use core::iter::Peekable;
 /// A iterator for deduping the key of a sorted iterator.
 /// When encountering the duplicated key, only the last key-value pair is yielded.
 ///
-/// Used by [`BTreeMap::bulk_build_from_sorted_iter`].
+/// Used by [`BTreeMap::bulk_build_from_sorted_iter`][1].
+///
+/// [1]: crate::collections::BTreeMap::bulk_build_from_sorted_iter
 pub struct DedupSortedIter<K, V, I>
 where
     I: Iterator<Item = (K, V)>,
diff --git a/library/alloc/src/collections/btree/map/entry.rs b/library/alloc/src/collections/btree/map/entry.rs
index b6eecf9b0..cd7cdc192 100644
--- a/library/alloc/src/collections/btree/map/entry.rs
+++ b/library/alloc/src/collections/btree/map/entry.rs
@@ -133,6 +133,17 @@ impl<'a, K: Debug + Ord, V: Debug, A: Allocator + Clone> fmt::Display
     }
 }
 
+#[cfg(not(bootstrap))]
+#[unstable(feature = "map_try_insert", issue = "82766")]
+impl<'a, K: core::fmt::Debug + Ord, V: core::fmt::Debug> core::error::Error
+    for crate::collections::btree_map::OccupiedError<'a, K, V>
+{
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        "key already exists"
+    }
+}
+
 impl<'a, K: Ord, V, A: Allocator + Clone> Entry<'a, K, V, A> {
     /// Ensures a value is in the entry by inserting the default if empty, and returns
     /// a mutable reference to the value in the entry.
diff --git a/library/alloc/src/collections/btree/node.rs b/library/alloc/src/collections/btree/node.rs
index d831161bc..f1d2d3b30 100644
--- a/library/alloc/src/collections/btree/node.rs
+++ b/library/alloc/src/collections/btree/node.rs
@@ -318,7 +318,7 @@ impl<BorrowType: marker::BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type>
     pub fn ascend(
         self,
     ) -> Result<Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>, Self> {
-        assert!(BorrowType::PERMITS_TRAVERSAL);
+        let _ = BorrowType::TRAVERSAL_PERMIT;
         // We need to use raw pointers to nodes because, if BorrowType is marker::ValMut,
         // there might be outstanding mutable references to values that we must not invalidate.
         let leaf_ptr: *const _ = Self::as_leaf_ptr(&self);
@@ -1003,7 +1003,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
     /// both, upon success, do nothing.
     pub fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
-        assert!(BorrowType::PERMITS_TRAVERSAL);
+        let _ = BorrowType::TRAVERSAL_PERMIT;
         // We need to use raw pointers to nodes because, if BorrowType is
         // marker::ValMut, there might be outstanding mutable references to
         // values that we must not invalidate. There's no worry accessing the
@@ -1666,15 +1666,17 @@ pub mod marker {
     pub struct ValMut<'a>(PhantomData<&'a mut ()>);
 
     pub trait BorrowType {
-        // Whether node references of this borrow type allow traversing
-        // to other nodes in the tree.
-        const PERMITS_TRAVERSAL: bool = true;
+        // If node references of this borrow type allow traversing to other
+        // nodes in the tree, this constant can be evaluated. Thus reading it
+        // serves as a compile-time assertion.
+        const TRAVERSAL_PERMIT: () = ();
     }
     impl BorrowType for Owned {
-        // Traversal isn't needed, it happens using the result of `borrow_mut`.
+        // Reject evaluation, because traversal isn't needed. Instead traversal
+        // happens using the result of `borrow_mut`.
         // By disabling traversal, and only creating new references to roots,
         // we know that every reference of the `Owned` type is to a root node.
-        const PERMITS_TRAVERSAL: bool = false;
+        const TRAVERSAL_PERMIT: () = panic!();
     }
     impl BorrowType for Dying {}
     impl<'a> BorrowType for Immut<'a> {}