LUCENE-9668: Deprecate MinShouldMatchSumScorer with WANDScorer (#2205)

Author: zacharymorn

lucene/core/src/java/org/apache/lucene/search/Boolean2ScorerSupplier.java

@@ -231,10 +231,15 @@ private Scorer opt(
         optionalScorers.add(scorer.get(leadCost));
       }
 
-      if (scoreMode == ScoreMode.TOP_SCORES) {
-        return new WANDScorer(weight, optionalScorers, minShouldMatch);
-      } else if (minShouldMatch > 1) {
-        return new MinShouldMatchSumScorer(weight, optionalScorers, minShouldMatch);
+      // Technically speaking, WANDScorer should be able to handle the following 3 conditions now
+      // 1. Any ScoreMode (with scoring or not)
+      // 2. Any minCompetitiveScore ( >= 0 )
+      // 3. Any minShouldMatch ( >= 0 )
+      //
+      // However, as WANDScorer uses more complex algorithm and data structure, we would like to
+      // still use DisjunctionSumScorer to handle exhaustive pure disjunctions, which may be faster
+      if (scoreMode == ScoreMode.TOP_SCORES || minShouldMatch > 1) {
+        return new WANDScorer(weight, optionalScorers, minShouldMatch, scoreMode);
       } else {
         return new DisjunctionSumScorer(weight, optionalScorers, scoreMode);
       }

lucene/core/src/java/org/apache/lucene/search/BooleanScorer.java

@@ -61,7 +61,7 @@ void score(LeafCollector collector, Bits acceptDocs, int min, int max) throws IO
     }
   }
 
-  // See MinShouldMatchSumScorer for an explanation
+  // See WANDScorer for an explanation
   private static long cost(Collection<BulkScorer> scorers, int minShouldMatch) {
     final PriorityQueue<BulkScorer> pq =
         new PriorityQueue<BulkScorer>(scorers.size() - minShouldMatch + 1) {