bors c7ce69faf2 Auto merge of #92962 - frank-king:btree_entry_no_insert, r=Amanieu
BTreeMap::entry: Avoid allocating if no insertion

This PR allows the `VacantEntry` to borrow from an empty tree with no root, and to lazily allocate a new root node when the user calls `.insert(value)`.
2022-03-20 11:20:26 +00:00
..