LUCENE-9953: Make FacetResult#value accurate for LongValueFacetCounts multi-value doc cases (#131)

Co-authored-by: Greg Miller <gmiller@amazon.com>

Author: gsmiller

lucene/CHANGES.txt

@@ -390,6 +390,10 @@ Bug Fixes
 
 * LUCENE-9958: Fixed performance regression for boolean queries that configure a
   minimum number of matching clauses. (Adrien Grand, Matt Weber)
+  
+* LUCENE-9953: LongValueFacetCounts should count each document at most once when determining
+  the total count for a dimension. Prior to this fix, multi-value docs could contribute a > 1
+  count to the dimension count. (Greg Miller)
 
 Other
 ---------------------

lucene/facet/src/java/org/apache/lucene/facet/FacetResult.java

@@ -28,9 +28,12 @@ public final class FacetResult {
   public final String[] path;
 
   /**
-   * Total value for this path (sum of all child counts, or sum of all child values), even those not
-   * included in the topN.
+   * Total number of documents containing a value for this path, even those not included in the
+   * topN. If a document contains multiple values for the same path, it will only be counted once in
+   * this value.
    */
+  // TODO: This may not hold true for SSDV faceting, where docs can be counted more than
+  // once. We should fix this. See LUCENE-9952
   public final Number value;
 
   /** How many child labels were encountered. */

lucene/facet/src/java/org/apache/lucene/facet/LongValueFacetCounts.java

@@ -160,7 +160,9 @@ private void count(String field, List<MatchingDocs> matchingDocs) throws IOExcep
 
         for (int doc = it.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = it.nextDoc()) {
           int limit = multiValues.docValueCount();
-          totCount += limit;
+          if (limit > 0) {
+            totCount++;
+          }
           for (int i = 0; i < limit; i++) {
             increment(multiValues.nextValue());
           }
@@ -204,7 +206,9 @@ private void countAll(IndexReader reader, String field) throws IOException {
 
         while (multiValues.nextDoc() != DocIdSetIterator.NO_MORE_DOCS) {
           int limit = multiValues.docValueCount();
-          totCount += limit;
+          if (limit > 0) {
+            totCount++;
+          }
           for (int i = 0; i < limit; i++) {
             increment(multiValues.nextValue());
           }

lucene/facet/src/test/org/apache/lucene/facet/TestLongValueFacetCounts.java

@@ -429,15 +429,15 @@ public void testRandomMultiValued() throws Exception {
       int expectedChildCount = 0;
       int expectedTotalCount = 0;
       for (int i = 0; i < valueCount; i++) {
-        if (values[i] != null) {
+        if (values[i] != null && values[i].length > 0) {
+          expectedTotalCount++;
           for (long value : values[i]) {
             Integer curCount = expected.get(value);
             if (curCount == null) {
               curCount = 0;
               expectedChildCount++;
             }
             expected.put(value, curCount + 1);
-            expectedTotalCount++;
           }
         }
       }
@@ -520,9 +520,9 @@ public void testRandomMultiValued() throws Exception {
       expectedChildCount = 0;
       int totCount = 0;
       for (int i = minId; i <= maxId; i++) {
-        if (values[i] != null) {
+        if (values[i] != null && values[i].length > 0) {
+          totCount++;
           for (long value : values[i]) {
-            totCount++;
             Integer curCount = expected.get(value);
             if (curCount == null) {
               expectedChildCount++;