Fix MissingValues for Lucene 10 (opensearch-project#17647)

With the Lucene 10 upgrade, we should not rely on doc values returning
NO_MORE_DOCS once they've run out of ords. Instead, we should return a
correct value for docValueCount().

Signed-off-by: Michael Froh <froh@amazon.com>

Author: msfroh

server/src/main/java/org/opensearch/search/aggregations/support/MissingValues.java

@@ -324,7 +324,8 @@ public boolean advanceExact(int doc) throws IOException {
 
             @Override
             public int docValueCount() {
-                return values.docValueCount();
+                // If we don't have ordinals, then we just have the missing value
+                return hasOrds ? values.docValueCount() : 1;
             }
 
             @Override
@@ -359,7 +360,8 @@ public long getValueCount() {
 
             @Override
             public int docValueCount() {
-                return Math.max(1, values.docValueCount());
+                // If we don't have ordinals, then we just have the missing value
+                return hasOrds ? values.docValueCount() : 1;
             }
 
             @Override

server/src/test/java/org/opensearch/search/aggregations/support/MissingValuesTests.java

@@ -152,7 +152,7 @@ public long nextOrd() {
                 if (i < ords[doc].length) {
                     return ords[doc][i++];
                 } else {
-                    return NO_MORE_DOCS;
+                    throw new IllegalStateException();
                 }
             }
 
@@ -175,13 +175,13 @@ public int docValueCount() {
             for (int i = 0; i < numDocs; ++i) {
                 assertTrue(withMissingReplaced.advanceExact(i));
                 if (ords[i].length > 0) {
+                    assertEquals(ords[i].length, withMissingReplaced.docValueCount());
                     for (int ord : ords[i]) {
                         assertEquals(values[ord], withMissingReplaced.lookupOrd(withMissingReplaced.nextOrd()));
                     }
-                    assertEquals(SortedSetDocValues.NO_MORE_DOCS, withMissingReplaced.nextOrd());
                 } else {
+                    assertEquals(1, withMissingReplaced.docValueCount());
                     assertEquals(missing, withMissingReplaced.lookupOrd(withMissingReplaced.nextOrd()));
-                    assertEquals(SortedSetDocValues.NO_MORE_DOCS, withMissingReplaced.nextOrd());
                 }
             }
         }