Cursor::set_last was panicking on empty pages

Dependencies

• [2] LSQ6V7M6 Cleanup + docs
• [3] OP6SVMOD Resetting history
• [4] ESUI5EUZ Making as_page() unsafe
• [5] OTWDDJE7 Trait/type cleanup
• [6] HN6Z5DU4 Cleanup
• [7] WS4ZQM4R Debugging, tests, etc.
• [8] OFINGD26 implementing prev() on cursors (+ some cleanup)

Change contents

• replacement in sanakirja-core/src/btree/cursor.rs at line 214
  [3.68135]→[2.19851:19950](∅→∅),[3.11688]→[3.68404:68443](∅→∅),[2.19950]→[3.68404:68443](∅→∅),[3.35118]→[3.68404:68443](∅→∅),[3.8621]→[3.68404:68443](∅→∅),[3.25312]→[3.68404:68443](∅→∅),[3.68404]→[3.68404:68443](∅→∅),[3.11744]→[3.68443:68466](∅→∅),[3.68443]→[3.68443:68466](∅→∅),[3.68466]→[3.11745:11830](∅→∅),[3.11830]→[3.15584:15635](∅→∅),[3.15635]→[3.11830:11856](∅→∅),[3.11830]→[3.11830:11856](∅→∅),[3.11916]→[3.68653:68672](∅→∅),[3.68653]→[3.68653:68672](∅→∅)
  − let (k, v, r) = P::current(txn, current.page.as_page(), &mut current.cursor).unwrap();

  − last_match = Some((k, v));

  − if r > 0 {

  − let page = txn.load_page(r)?;

  − self.push(PageCursor {

  − cursor: P::cursor_last(&page),

  − page,

  − })
  [3.68135]

  [3.68672]
  + if let Some((k, v, r)) = P::current(txn, current.page.as_page(), &mut current.cursor) {

  + last_match = Some((k, v));

  + if r > 0 {

  + let page = txn.load_page(r)?;

  + self.push(PageCursor {

  + cursor: P::cursor_last(&page),

  + page,

  + })

  + } else {

  + break;

  + }
• replacement in sanakirja-core/src/btree/cursor.rs at line 226
  [3.68693]→[3.68693:68716](∅→∅)
  − break;
  [3.68693]

  [3.68716]
  + // The page is empty, meaning there's no right or left child.

  + debug_assert!(P::is_init(&current.cursor));

  + // Assert we're looking at the root.

  + debug_assert_eq!(self.len, 1);

  + // And the root has no child.

  + debug_assert_eq!(P::right_child(current.page.as_page(), &current.cursor), 0);

  + return Ok(None);