HSEARCH-4577 Some cleanups

Author: marko-bekhta

backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/logging/impl/Log.java

@@ -602,7 +602,7 @@ SearchException invalidFieldValueType(@FormatWith(ClassFormatter.class) Class<?>
 	@Message(id = ID_OFFSET + 113,
 			value = "Invalid cardinality for projection on field '%1$s': the projection is single-valued,"
 					+ " but this field is multi-valued."
-					+ " Make sure to call '.multi()' when you create the projection.")
+					+ " Make sure to call '.accumulator(...)' when you create the projection.")
 	SearchException invalidSingleValuedProjectionOnMultiValuedField(String absolutePath, @Param EventContext context);
 
 	@Message(id = ID_OFFSET + 117,

backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/query/dsl/impl/ElasticsearchSearchQuerySelectStepImpl.java

@@ -83,7 +83,7 @@ public <P> ElasticsearchSearchQueryWhereStep<P, LOS> select(SearchProjection<P>
 	public ElasticsearchSearchQueryWhereStep<List<?>, LOS> select(SearchProjection<?>... projections) {
 		return select( scope.projectionBuilders().composite()
 				.build( projections, ProjectionCompositor.fromList( projections.length ),
-						ProjectionAccumulator.single() ) );
+						ProjectionAccumulator.nullable() ) );
 	}
 
 	@Override

backend/lucene/src/main/java/org/hibernate/search/backend/lucene/logging/impl/Log.java

@@ -537,7 +537,7 @@ SearchException invalidFieldValueType(@FormatWith(ClassFormatter.class) Class<?>
 	@Message(id = ID_OFFSET + 131,
 			value = "Invalid cardinality for projection on field '%1$s': the projection is single-valued,"
 					+ " but this field is multi-valued."
-					+ " Make sure to call '.multi()' when you create the projection.")
+					+ " Make sure to call '.accumulator(...)' when you create the projection.")
 	SearchException invalidSingleValuedProjectionOnMultiValuedField(String absolutePath, @Param EventContext context);
 
 	@Message(id = ID_OFFSET + 135,
@@ -600,9 +600,9 @@ SearchException invalidContextForProjectionOnField(String absolutePath,
 			value = "Invalid cardinality for projection on field '%1$s': the projection is single-valued,"
 					+ " but this field is effectively multi-valued in this context,"
 					+ " because parent object field '%2$s' is multi-valued."
-					+ " Either call '.multi()' when you create the projection on field '%1$s',"
+					+ " Either call '.accumulator(...)' when you create the projection on field '%1$s',"
 					+ " or wrap that projection in an object projection like this:"
-					+ " 'f.object(\"%2$s\").from(<the projection on field %1$s>).as(...).multi()'.")
+					+ " 'f.object(\"%2$s\").from(<the projection on field %1$s>).as(...).accumulator(...)'.")
 	SearchException invalidSingleValuedProjectionOnValueFieldInMultiValuedObjectField(String absolutePath,
 			String objectFieldAbsolutePath);
 

backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/query/dsl/impl/LuceneSearchQuerySelectStepImpl.java

@@ -81,7 +81,7 @@ public <P> LuceneSearchQueryWhereStep<P, LOS> select(SearchProjection<P> project
 	public LuceneSearchQueryWhereStep<List<?>, LOS> select(SearchProjection<?>... projections) {
 		return select( scope.projectionBuilders().composite()
 				.build( projections, ProjectionCompositor.fromList( projections.length ),
-						ProjectionAccumulator.single() ) );
+						ProjectionAccumulator.nullable() ) );
 	}
 
 	@Override

engine/src/main/java/org/hibernate/search/engine/search/projection/ProjectionAccumulator.java

@@ -39,8 +39,8 @@
  */
 public interface ProjectionAccumulator<E, V, A, R> {
 
-	static <V> ProjectionAccumulator.Provider<V, V> single() {
-		return BuiltInProjectionAccumulators.single();
+	static <V> ProjectionAccumulator.Provider<V, V> nullable() {
+		return BuiltInProjectionAccumulators.nullable();
 	}
 
 	static <V> Provider<V, List<V>> list() {

engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/ConstantProjectionDefinition.java

@@ -54,7 +54,7 @@ public static <T> BeanHolder<ConstantProjectionDefinition<List<T>>> emptyList()
 	public static <T> BeanHolder<ConstantProjectionDefinition<T>> empty(ProjectionAccumulator.Provider<?, T> accumulator) {
 		T empty = accumulator.get().empty();
 
-		if ( ProjectionAccumulator.single().equals( accumulator ) ) {
+		if ( ProjectionAccumulator.nullable().equals( accumulator ) ) {
 			return nullValue();
 		}
 		if ( ProjectionAccumulator.optional().equals( accumulator ) ) {

engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/CompositeProjectionValueStep.java

@@ -37,7 +37,9 @@ public interface CompositeProjectionValueStep<N extends CompositeProjectionOptio
 	 * @deprecated Use {@link #accumulator(ProjectionAccumulator.Provider)} instead.
 	 */
 	@Deprecated(since = "8.0")
-	CompositeProjectionOptionsStep<?, List<T>> multi();
+	default CompositeProjectionOptionsStep<?, List<T>> multi() {
+		return accumulator( ProjectionAccumulator.list() );
+	}
 
 	/**
 	 * Defines how to accumulate composite projection values.

engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/DistanceToFieldProjectionValueStep.java

@@ -34,7 +34,9 @@ public interface DistanceToFieldProjectionValueStep<N extends DistanceToFieldPro
 	 * @deprecated Use {@link #accumulator(ProjectionAccumulator.Provider)} instead.
 	 */
 	@Deprecated(since = "8.0")
-	DistanceToFieldProjectionOptionsStep<?, List<T>> multi();
+	default DistanceToFieldProjectionOptionsStep<?, List<T>> multi() {
+		return accumulator( ProjectionAccumulator.list() );
+	}
 
 	/**
 	 * Defines how to accumulate distance projection values.

engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/FieldProjectionValueStep.java

@@ -34,7 +34,9 @@ public interface FieldProjectionValueStep<N extends FieldProjectionOptionsStep<?
 	 * @deprecated Use {@link #accumulator(ProjectionAccumulator.Provider)} instead.
 	 */
 	@Deprecated(since = "8.0")
-	FieldProjectionOptionsStep<?, List<T>> multi();
+	default FieldProjectionOptionsStep<?, List<T>> multi() {
+		return accumulator( ProjectionAccumulator.list() );
+	}
 
 	/**
 	 * Defines how to accumulate field projection values.

engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/CompositeProjectionValueStepImpl.java

@@ -4,8 +4,6 @@
  */
 package org.hibernate.search.engine.search.projection.dsl.impl;
 
-import java.util.List;
-
 import org.hibernate.search.engine.search.projection.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.CompositeProjectionOptionsStep;
@@ -19,12 +17,7 @@ public class CompositeProjectionValueStepImpl<T>
 
 	public CompositeProjectionValueStepImpl(CompositeProjectionBuilder builder,
 			SearchProjection<?>[] inners, ProjectionCompositor<?, T> compositor) {
-		super( builder, inners, compositor, ProjectionAccumulator.single() );
-	}
-
-	@Override
-	public CompositeProjectionOptionsStep<?, List<T>> multi() {
-		return accumulator( ProjectionAccumulator.list() );
+		super( builder, inners, compositor, ProjectionAccumulator.nullable() );
 	}
 
 	@Override