It seems like the key_value function has been removed from Cursor in 1.78.0-nightly. I've been using this to get the key/value pair from BTreeMap::upper_bound and BTreeMap::lower_bound.

Does anyone know why this was removed and what a good idiomatic alternative would be?

Edit: In case anyone encounters the same problem and is curious what's going on (the documentation hasn't been updated to reflect the change yet), it was referred to in this issue: 107540 changed in this commit: 8ee9693. Essentially, cursors in BTreeMaps previously pointed to specific nodes in the tree whereas now they point to gaps between the nodes. To get the node values, you need to use prev or next on the cursors returned by upper_bound or lower_bound.