HSEARCH-4173 Assume no value in the Elasticsearch geo_distance sort i…

…f the target field doesn't exist in one of the targeted indexes

Signed-off-by: Yoann Rodière <yoann@hibernate.org>

backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/lowlevel/syntax/search/impl/Elasticsearch60SearchSyntax.java

@@ -28,4 +28,12 @@ public void requestDocValues(JsonObject requestBody, JsonPrimitive fieldName) {
 		// So we just don't specify a format.
 		DOCVALUE_FIELDS_ACCESSOR.addElementIfAbsent( requestBody, fieldName );
 	}
+
+	@Override
+	public void requestGeoDistanceSortIgnoreUnmapped(JsonObject innerObject) {
+		// Support for ignore_unmapped in geo_distance sorts added in 6.4:
+		// https://github.com/elastic/elasticsearch/pull/31153
+		// In 6.3 and below, we just can't ignore unmapped fields,
+		// which means sorts will fail when the geo_point field is not present in all indexes.
+	}
 }

backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/lowlevel/syntax/search/impl/Elasticsearch7SearchSyntax.java

@@ -26,6 +26,8 @@ public class Elasticsearch7SearchSyntax implements ElasticsearchSearchSyntax {
 	private static final JsonAccessor<JsonElement> NESTED_ACCESSOR = JsonAccessor.root().property( "nested" );
 	private static final JsonAccessor<JsonElement> PATH_ACCESSOR = JsonAccessor.root().property( "path" );
 	private static final JsonAccessor<JsonElement> FILTER_ACCESSOR = JsonAccessor.root().property( "filter" );
+	private static final JsonAccessor<Boolean> IGNORE_UNMAPPED_ACCESSOR =
+			JsonAccessor.root().property( "ignore_unmapped" ).asBoolean();
 
 	@Override
 	public String getTermAggregationOrderByTermToken() {
@@ -55,4 +57,9 @@ public void requestNestedSort(List<String> nestedPathHierarchy, JsonObject inner
 			nextNestedObjectTarget = nestedObject;
 		}
 	}
+
+	@Override
+	public void requestGeoDistanceSortIgnoreUnmapped(JsonObject innerObject) {
+		IGNORE_UNMAPPED_ACCESSOR.set( innerObject, true );
+	}
 }

backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/lowlevel/syntax/search/impl/ElasticsearchSearchSyntax.java

@@ -19,4 +19,6 @@ public interface ElasticsearchSearchSyntax {
 
 	void requestNestedSort(List<String> nestedPathHierarchy, JsonObject innerObject, JsonObject filterOrNull);
 
+	void requestGeoDistanceSortIgnoreUnmapped(JsonObject innerObject);
+
 }

backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/types/sort/impl/AbstractElasticsearchDocumentValueSort.java

@@ -40,7 +40,7 @@ abstract class AbstractElasticsearchDocumentValueSort extends AbstractElasticsea
 
 	protected final String absoluteFieldPath;
 	protected final List<String> nestedPathHierarchy;
-	private final ElasticsearchSearchSyntax searchSyntax;
+	protected final ElasticsearchSearchSyntax searchSyntax;
 
 	private final JsonPrimitive mode;
 	private final ElasticsearchSearchPredicate filter;

backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/types/sort/impl/ElasticsearchDistanceSort.java

@@ -41,6 +41,11 @@ private ElasticsearchDistanceSort(Builder builder) {
 	@Override
 	protected void doToJsonSorts(ElasticsearchSearchSortCollector collector, JsonObject innerObject) {
 		innerObject.add( absoluteFieldPath, ElasticsearchGeoPointFieldCodec.INSTANCE.encode( center ) );
+		if ( indexNames.size() > 1 ) {
+			// There are multiple target indexes; some of them may not declare the field.
+			// Instruct ES to behave as if the field had no value in that case.
+			searchSyntax.requestGeoDistanceSortIgnoreUnmapped( innerObject );
+		}
 
 		JsonObject outerObject = new JsonObject();
 		GEO_DISTANCE_ACCESSOR.add( outerObject, innerObject );