Fixing a double-free of roots after deletions (the root was freed both by handle_merge and by update_root)

Dependencies

• [2] OFINGD26 implementing prev() on cursors (+ some cleanup)
• [3] W26CFMAQ Improving safety of cursors
• [4] OP6SVMOD Resetting history
• [5] QEUTVAZ4 Splitting btree::page
• [6] UUUVNC4D Debugging/cleanup around cursors
• [7] OTWDDJE7 Trait/type cleanup

Change contents

• edit in sanakirja-core/src/btree/del.rs at line 393
  [3.37905]

  [3.2311]
  + debug!(

  + "handle_merge for level {:?}, freed {:?}",

  + cursor.pointer(),

  + freed

  + );
• replacement in sanakirja-core/src/btree/del.rs at line 399
  [3.2361]→[3.446:490](∅→∅)
  − free[cursor.pointer() + 1] = freed;
  [3.2361]

  [3.62825]
  + free[cursor.pointer()] = freed;
• replacement in sanakirja-core/src/btree/del.rs at line 543
  [3.38675]→[3.38675:38716](∅→∅),[3.38716]→[3.491:535](∅→∅),[3.535]→[3.38716:38748](∅→∅),[3.38716]→[3.38716:38748](∅→∅),[3.38748]→[2.10591:10625](∅→∅),[2.10625]→[3.38775:38785](∅→∅),[3.38775]→[3.38775:38785](∅→∅)
  − Put::Ok(Ok { page, freed }) => {

  − debug!("ok freed {:?}", freed);

  − free[0][0] = freed;

  − db.db = page.0.offset

  − }
  [3.38675]

  [3.38785]
  + Put::Ok(Ok { page, .. }) => db.db = page.0.offset,
• replacement in sanakirja-core/src/btree/del.rs at line 549
  [3.38891]→[3.38891:38910](∅→∅)
  − freed,
  [3.38891]

  [3.38910]
  + ..
• edit in sanakirja-core/src/btree/del.rs at line 551
  [3.38925]→[3.536:583](∅→∅),[3.583]→[3.38925:38957](∅→∅),[3.38925]→[3.38925:38957](∅→∅)
  − debug!("split freed {:?}", freed);

  − free[0][0] = freed;