fixes based on review

Author: hmottestad

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/iterator/GroupIterator.java

@@ -8,6 +8,7 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  *******************************************************************************/
+// Some portions generated by Codex
 package org.eclipse.rdf4j.query.algebra.evaluation.iterator;
 
 import java.util.ArrayList;
@@ -332,7 +333,7 @@ private List<Entry> emptySolutionSpecialCase(List<AggregatePredicateCollectorSup
 						// Even in the case that the Count is of a constant value.
 						predicates.add(ALWAYS_FALSE_VALUE);
 					} else {
-						predicates.add(ALWAYS_TRUE_VALUE);
+						predicates.add(ag.makePotentialDistinctTest.get());
 					}
 				}
 				final Entry entry = new Entry(null, collectors, predicates);

core/queryalgebra/evaluation/src/test/java/org/eclipse/rdf4j/query/algebra/evaluation/iterator/GroupIteratorTest.java

@@ -8,6 +8,7 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  *******************************************************************************/
+// Some portions generated by Codex
 package org.eclipse.rdf4j.query.algebra.evaluation.iterator;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -315,6 +316,23 @@ public void testCustomNAryAggregateFunction_Empty() throws QueryEvaluationExcept
 		}
 	}
 
+	@Test
+	public void testCustomNAryAggregateFunction_Empty_DistinctTuplePredicateInvoked() throws QueryEvaluationException {
+		AggregateNAryFunctionFactory nAryFactory = new DistinctTupleTouchingAggregateNAryFunctionFactory();
+		CustomAggregateNAryFunctionRegistry.getInstance().add(nAryFactory);
+		try {
+			Group group = new Group(EMPTY_ASSIGNMENT);
+			group.addGroupElement(new GroupElem("naryDistinct",
+					new AggregateFunctionCall(List.of(Var.of("a"), Var.of("b")), nAryFactory.getIri(), false)));
+			try (GroupIterator gi = new GroupIterator(EVALUATOR, group, EmptyBindingSet.getInstance(), CONTEXT)) {
+				assertThat(gi.next().getBinding("naryDistinct").getValue())
+						.isEqualTo(VF.createLiteral("0", XSD.INTEGER));
+			}
+		} finally {
+			CustomAggregateNAryFunctionRegistry.getInstance().remove(nAryFactory);
+		}
+	}
+
 	@Test
 	public void testCustomNAryAggregateFunction_WrongIri() throws QueryEvaluationException {
 		Group group = new Group(EMPTY_ASSIGNMENT);
@@ -475,6 +493,35 @@ public SumCollector getCollector() {
 		}
 	}
 
+	private static final class DistinctTupleTouchingAggregateNAryFunctionFactory
+			implements AggregateNAryFunctionFactory {
+		@Override
+		public String getIri() {
+			return "https://www.rdf4j.org/aggregate#nary-distinct-touching";
+		}
+
+		@Override
+		public AggregateNAryFunction<SumCollector, Value> buildFunction(
+				BiFunction<Integer, BindingSet, Value> evaluationStepByIndex) {
+			return new AggregateNAryFunction<>(evaluationStepByIndex) {
+
+				@Override
+				public void processAggregate(BindingSet bindingSet, Predicate<List<Value>> distinctValue,
+						SumCollector sumCollector) throws QueryEvaluationException {
+					List<Value> tuple = new ArrayList<>(2);
+					tuple.add(evaluate(0, bindingSet));
+					tuple.add(evaluate(1, bindingSet));
+					distinctValue.test(tuple);
+				}
+			};
+		}
+
+		@Override
+		public SumCollector getCollector() {
+			return new SumCollector();
+		}
+	}
+
 	/**
 	 * Dummy collector to verify custom aggregate functions
 	 */

core/queryalgebra/model/src/main/java/org/eclipse/rdf4j/query/algebra/AggregateFunctionCall.java

@@ -8,6 +8,7 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  ******************************************************************************/
+// Some portions generated by Codex
 
 package org.eclipse.rdf4j.query.algebra;
 
@@ -33,7 +34,7 @@ public AggregateFunctionCall(String iri, boolean distinct) {
 	}
 
 	public AggregateFunctionCall(List<ValueExpr> args, String iri, boolean distinct) {
-		super(args, distinct);
+		super(args instanceof ArrayList ? args : new ArrayList<>(args), distinct);
 		this.iri = iri;
 	}
 

core/queryalgebra/model/src/main/java/org/eclipse/rdf4j/query/algebra/NAryValueOperator.java

@@ -51,6 +51,9 @@ protected NAryValueOperator(List<ValueExpr> args) {
 
 	public void setArguments(List<ValueExpr> args) {
 		this.args = args;
+		for (ValueExpr arg : args) {
+			arg.setParentNode(this);
+		}
 	}
 
 	public List<ValueExpr> getArguments() {

core/queryalgebra/model/src/test/java/org/eclipse/rdf4j/query/algebra/AggregateFunctionCallTest.java

@@ -0,0 +1,41 @@
+/*******************************************************************************
+ * Copyright (c) 2026 Eclipse RDF4J contributors.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Distribution License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *******************************************************************************/
+// Some portions generated by Codex
+package org.eclipse.rdf4j.query.algebra;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+
+import org.eclipse.rdf4j.model.impl.SimpleValueFactory;
+import org.junit.jupiter.api.Test;
+
+class AggregateFunctionCallTest {
+
+	@Test
+	void constructorSetsParentForEachArgument() {
+		Var argument = Var.of("a");
+		AggregateFunctionCall aggregateFunctionCall = new AggregateFunctionCall(List.of(argument), "urn:test", false);
+
+		assertThat(argument.getParentNode()).isSameAs(aggregateFunctionCall);
+	}
+
+	@Test
+	void constructorCopiesArgumentsIntoMutableList() {
+		Var argument = Var.of("a");
+		AggregateFunctionCall aggregateFunctionCall = new AggregateFunctionCall(List.of(argument), "urn:test", false);
+		ValueConstant replacement = new ValueConstant(SimpleValueFactory.getInstance().createLiteral(1));
+
+		aggregateFunctionCall.replaceChildNode(argument, replacement);
+
+		assertThat(aggregateFunctionCall.getArguments()).containsExactly(replacement);
+	}
+}