HSEARCH-5334 Better handle advancing to the same parent doc

Author: marko-bekhta

backend/lucene/src/main/java/org/hibernate/search/backend/lucene/lowlevel/docvalues/impl/DoubleMultiValuesToSingleValuesSource.java

@@ -138,6 +138,7 @@ protected NumericDoubleValues select(SortedNumericDoubleDocValues values, ChildD
 
 			int lastSeenParentDoc = -1;
 			double lastEmittedValue = -1;
+			boolean result = false;
 
 			@Override
 			public double doubleValue() {
@@ -148,16 +149,18 @@ public double doubleValue() {
 			public boolean advanceExact(int parentDoc) throws IOException {
 				assert parentDoc >= lastSeenParentDoc : "can only evaluate current and upcoming parent docs";
 				if ( parentDoc == lastSeenParentDoc ) {
-					return true;
+					return result;
 				}
 
+				lastSeenParentDoc = parentDoc;
 				if ( !childDocsWithValues.advanceExactParent( parentDoc ) ) {
 					// No child of this parent has a value
+					result = false;
 					return false;
 				}
 
-				lastSeenParentDoc = parentDoc;
 				lastEmittedValue = mode.pick( values, childDocsWithValues );
+				result = true;
 				return true;
 			}
 

backend/lucene/src/main/java/org/hibernate/search/backend/lucene/lowlevel/docvalues/impl/LongMultiValuesToSingleValuesSource.java

@@ -160,6 +160,7 @@ protected LongValues select(SortedNumericDocValues values, ChildDocIds childDocs
 		return new LongValues() {
 			int lastSeenParentDoc = -1;
 			long lastEmittedValue = -1;
+			boolean result = false;
 
 			@Override
 			public long longValue() {
@@ -170,16 +171,18 @@ public long longValue() {
 			public boolean advanceExact(int parentDoc) throws IOException {
 				assert parentDoc >= lastSeenParentDoc : "can only evaluate current and upcoming parent docs";
 				if ( parentDoc == lastSeenParentDoc ) {
-					return true;
+					return result;
 				}
 
+				lastSeenParentDoc = parentDoc;
 				if ( !childDocsWithValues.advanceExactParent( parentDoc ) ) {
 					// No child of this parent has a value
+					result = false;
 					return false;
 				}
 
-				lastSeenParentDoc = parentDoc;
 				lastEmittedValue = mode.pick( values, childDocsWithValues );
+				result = true;
 				return true;
 			}
 		};

backend/lucene/src/main/java/org/hibernate/search/backend/lucene/lowlevel/docvalues/impl/TextMultiValuesToSingleValuesSource.java

@@ -120,6 +120,7 @@ protected SortedDocValues select(SortedSetDocValues values, ChildDocIds childDoc
 		return new SortedSetDocValuesToSortedDocValuesWrapper( values ) {
 			int lastSeenParentDoc = -1;
 			int lastEmittedOrd = -1;
+			boolean result = false;
 
 			@Override
 			public int ordValue() {
@@ -135,16 +136,18 @@ public int docID() {
 			public boolean advanceExact(int parentDoc) throws IOException {
 				assert parentDoc >= lastSeenParentDoc : "can only evaluate current and upcoming parent docs";
 				if ( parentDoc == lastSeenParentDoc ) {
-					return true;
+					return result;
 				}
+				lastSeenParentDoc = parentDoc;
 
 				if ( !childDocsWithValues.advanceExactParent( parentDoc ) ) {
 					// No child of this parent has a value
+					result = false;
 					return false;
 				}
 
-				lastSeenParentDoc = parentDoc;
 				lastEmittedOrd = (int) mode.pick( values, childDocsWithValues );
+				result = true;
 				return true;
 			}
 		};

integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/sort/FieldSortBaseIT.java

@@ -9,6 +9,7 @@
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.hibernate.search.util.impl.integrationtest.common.assertion.SearchHitsAssert.assertThatHits;
 import static org.hibernate.search.util.impl.integrationtest.common.assertion.SearchResultAssert.assertThatQuery;
+import static org.hibernate.search.util.impl.integrationtest.common.assertion.SearchResultAssert.assertThatResult;
 import static org.hibernate.search.util.impl.integrationtest.mapper.stub.StubMapperUtils.documentProvider;
 import static org.junit.Assume.assumeFalse;
 import static org.junit.Assume.assumeTrue;
@@ -528,6 +529,22 @@ public void missingValue_multipleOptionsSameTime() {
 						dataSet.emptyDoc1Id );
 	}
 
+	@Test
+	public void missingValue_singleElement() {
+		assumeTestParametersWork();
+
+		DataSet<F> dataSet;
+		SearchQuery<DocumentReference> query;
+
+		String fieldPath = getFieldPath();
+
+		// Explicit order with missing().last()
+		dataSet = dataSetForAsc;
+		query = matchNonEmptyAndEmpty1Query( dataSet, f -> f.field( fieldPath ).asc().missing().lowest() );
+		assertThatResult( query.fetch( 0, 1 ) )
+				.hasDocRefHitsExactOrder( index.typeName(), dataSet.emptyDoc1Id );
+	}
+
 	private SearchQuery<DocumentReference> matchNonEmptyQuery(DataSet<F> dataSet,
 			Function<? super SearchSortFactory, ? extends FieldSortOptionsStep<?, ?>> sortContributor) {
 		return matchNonEmptyQuery( dataSet, sortContributor, index.createScope() );