LUCENE-9565 Fix competitive iteration

PR apache#1351 introduced a sort optimization where documents can be skipped.
But iteration over competitive iterators was not properly organized,
as they were not storing the current docID, and
when competitive iterator was updated the current doc ID was lost.

This patch fixed it.

Relates to apache#1351

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

@@ -204,9 +204,14 @@ public int score(LeafCollector collector, Bits acceptDocs, int min, int max) thr
       collector.setScorer(scorer);
       DocIdSetIterator scorerIterator = twoPhase == null ? iterator : twoPhase.approximation();
       DocIdSetIterator collectorIterator = collector.competitiveIterator();
-      // if possible filter scorerIterator to keep only competitive docs as defined by collector
-      DocIdSetIterator filteredIterator = collectorIterator == null ? scorerIterator :
-          ConjunctionDISI.intersectIterators(Arrays.asList(scorerIterator, collectorIterator));
+      DocIdSetIterator filteredIterator = scorerIterator;
+      if (collectorIterator != null) {
+        if (scorerIterator.docID() != -1) {
+          collectorIterator.advance(scorerIterator.docID());
+        }
+        // filter scorerIterator to keep only competitive docs as defined by collector
+        filteredIterator = ConjunctionDISI.intersectIterators(Arrays.asList(scorerIterator, collectorIterator));
+      }
       if (filteredIterator.docID() == -1 && min == 0 && max == DocIdSetIterator.NO_MORE_DOCS) {
         scoreAll(collector, filteredIterator, twoPhase, acceptDocs);
         return DocIdSetIterator.NO_MORE_DOCS;

lucene/core/src/java/org/apache/lucene/search/comparators/DocComparator.java

@@ -133,14 +133,16 @@ public DocIdSetIterator competitiveIterator() {
                 return null;
             } else {
                 return new DocIdSetIterator() {
+                    private int docID = -1;
+
                     @Override
                     public int nextDoc() throws IOException {
-                        return competitiveIterator.nextDoc();
+                        return advance(docID + 1);
                     }
 
                     @Override
                     public int docID() {
-                        return competitiveIterator.docID();
+                        return docID;
                     }
 
                     @Override
@@ -150,7 +152,7 @@ public long cost() {
 
                     @Override
                     public int advance(int target) throws IOException {
-                        return competitiveIterator.advance(target);
+                        return docID = competitiveIterator.advance(target);
                     }
                 };
             }

lucene/core/src/java/org/apache/lucene/search/comparators/NumericComparator.java

@@ -220,14 +220,16 @@ public PointValues.Relation compare(byte[] minPackedValue, byte[] maxPackedValue
         public DocIdSetIterator competitiveIterator() {
             if (enableSkipping == false) return null;
             return new DocIdSetIterator() {
+                private int docID = -1;
+
                 @Override
                 public int nextDoc() throws IOException {
-                    return competitiveIterator.nextDoc();
+                    return advance(docID + 1);
                 }
 
                 @Override
                 public int docID() {
-                    return competitiveIterator.docID();
+                    return docID;
                 }
 
                 @Override
@@ -237,7 +239,7 @@ public long cost() {
 
                 @Override
                 public int advance(int target) throws IOException {
-                    return competitiveIterator.advance(target);
+                    return docID = competitiveIterator.advance(target);
                 }
             };
         }