[nh2]

Disclosure: This is the outcome of me debugging an assertion failure (I encountered from 1.5.5 to 1.7.1) with the Claude Opus 4.6 LLM.

As far as I can tell, the minimal repro it generated for me makes sense.

I am not 100% confident about the fix to the assertion, so please do review that with extra scrutiny @yzabalotski and @jlblancoc (from #250).

LLM output below.

---

The assertion assert(left < obj.dataset_.kdtree_get_point_count()) added in commit

549a5e32 - Fix middleSplit_ for same points

(PR #250, released in v1.6.2) incorrectly fires when using KDTreeSingleIndexDynamicAdaptor with repeated removePoint/addPoints cycles on the same point indices.

Root cause: addPoints increments the internal pointCount_ unconditionally, even when re-adding a previously removed point. This causes sub-tree vAcc_ vectors to accumulate more entries than dataset_.kdtree_get_point_count(). When buildIndex() is called on such a sub-tree, it sets size_ = vAcc_.size() and calls divideTree(*this, 0, size_, ...). In recursive calls, left (an offset into vAcc_) can exceed kdtree_get_point_count(), triggering the assertion.

However, the actual point indices stored in vAcc_ are always valid (they are always < N). The assertion conflates the array offset with the dataset size, which is only a valid invariant for the static adaptor where vAcc_ is a permutation of [0, N).

Fix: Change the assertion to check what actually matters -- that the point index at vAcc_[left] is within bounds of the dataset.

Add a repro test that exercises repeated removePoint/addPoints cycles. That fails without the fix.

LLM: Found, repro'd, and fixed using Claude Opus 4.6, human review.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.29%. Comparing base (ba47cfc) to head (e18f366).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #283      +/-   ##
==========================================
+ Coverage   83.85%   84.29%   +0.44%     
==========================================
  Files           1        1              
  Lines         675      675              
  Branches      127      128       +1     
==========================================
+ Hits          566      569       +3     
+ Misses        109      106       -3     

Files with missing lines	Coverage Δ
include/nanoflann.hpp	84.29% <100.00%> (+0.44%)	⬆️

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