Merge branch 'main' into changelogs-08-04

Author: lcawl

muted-tests.yml

@@ -592,9 +592,6 @@ tests:
 - class: org.elasticsearch.xpack.esql.qa.single_node.EsqlSpecApproximationBucketIncludeEmptyBucketsIT
   method: test {csv-spec:bucket_include_empty_buckets.Large number of buckets doesn't OOM - stats}
   issue: https://github.com/elastic/elasticsearch/issues/155921
-- class: org.elasticsearch.index.codec.vectors.cluster.FloatHierarchicalKMeansTests
-  method: testSoarAssignmentsValidAfterEmptyClusterRemoval
-  issue: https://github.com/elastic/elasticsearch/issues/155931
 - class: org.elasticsearch.test.rest.ClientYamlTestSuiteIT
   method: test {yaml=search.highlight/70_number_of_fragments/number_of_fragments at the maximum should SUCCEED}
   issue: https://github.com/elastic/elasticsearch/issues/155969

server/src/main/java/org/elasticsearch/index/codec/vectors/cluster/Soar.java

@@ -202,6 +202,10 @@ private static <V> int computeSoarAssignment(
         float[] distances,
         CentroidOps<V> ops
     ) {
+        if (centroidCount <= 0) {
+            // no other centroid available to spill to (e.g. an empty neighborhood after empty-cluster removal)
+            return NO_SOAR_ASSIGNMENT;
+        }
         V currentCentroid = centroids[currAssignment];
         float vectorCentroidDist = ops.squareDistance(vector, currentCentroid);
         if (vectorCentroidDist <= SOAR_MIN_DISTANCE) {