GH-4769 Variables that are not in scope should be hidden from filters.

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/impl/DefaultEvaluationStrategy.java

@@ -11,8 +11,10 @@
 package org.eclipse.rdf4j.query.algebra.evaluation.impl;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
+import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 import java.util.function.BiFunction;
@@ -165,7 +167,9 @@
 import org.eclipse.rdf4j.query.algebra.evaluation.util.QueryEvaluationUtility;
 import org.eclipse.rdf4j.query.algebra.evaluation.util.ValueComparator;
 import org.eclipse.rdf4j.query.algebra.evaluation.util.XMLDatatypeMathUtil;
+import org.eclipse.rdf4j.query.algebra.helpers.AbstractQueryModelVisitor;
 import org.eclipse.rdf4j.query.impl.EmptyBindingSet;
+import org.eclipse.rdf4j.query.parser.sparql.ast.VisitorException;
 import org.eclipse.rdf4j.util.UUIDable;
 
 import com.google.common.base.Stopwatch;
@@ -621,20 +625,25 @@ protected QueryEvaluationStep prepare(Service service, QueryEvaluationContext co
 
 	protected QueryEvaluationStep prepare(Filter node, QueryEvaluationContext context) throws QueryEvaluationException {
 
-		QueryEvaluationStep arg = precompile(node.getArg(), context);
+		final FilterIterator.RetainedVariableFilteredQueryEvaluationContext context2 = new FilterIterator.RetainedVariableFilteredQueryEvaluationContext(
+				node, context);
+		QueryEvaluationStep arg = precompile(node.getArg(), context2);
 		QueryValueEvaluationStep ves;
 		try {
-			ves = precompile(node.getCondition(), context);
-		} catch (QueryEvaluationException e) {
-			// If we have a failed compilation we always return false.
-			// Which means empty. so let's short circuit that.
-//			ves = new QueryValueEvaluationStep.ConstantQueryValueEvaluationStep(BooleanLiteral.FALSE);
-			return new QueryEvaluationStep() {
+			var ves2 = precompile(node.getCondition(), context2);
+			ves = new QueryValueEvaluationStep() {
+
 				@Override
-				public CloseableIteration<BindingSet, QueryEvaluationException> evaluate(BindingSet bs) {
-					return new EmptyIteration<>();
+				public Value evaluate(BindingSet bindings) throws QueryEvaluationException {
+					assert (node != null);
+					return ves2.evaluate(bindings);
 				}
+
 			};
+		} catch (QueryEvaluationException e) {
+			// If we have a failed compilation we always return false.
+			// Which means empty. so let's short circuit that.
+			return QueryEvaluationStep.EMPTY;
 		}
 		return new QueryEvaluationStep() {
 

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

@@ -10,6 +10,8 @@
  *******************************************************************************/
 package org.eclipse.rdf4j.query.algebra.evaluation.iterator;
 
+import java.util.HashSet;
+import java.util.Set;
 import java.util.function.BiConsumer;
 import java.util.function.Predicate;
 
@@ -22,13 +24,17 @@
 import org.eclipse.rdf4j.query.Dataset;
 import org.eclipse.rdf4j.query.MutableBindingSet;
 import org.eclipse.rdf4j.query.QueryEvaluationException;
+import org.eclipse.rdf4j.query.algebra.BindingSetAssignment;
 import org.eclipse.rdf4j.query.algebra.Filter;
 import org.eclipse.rdf4j.query.algebra.QueryModelNode;
 import org.eclipse.rdf4j.query.algebra.SubQueryValueOperator;
+import org.eclipse.rdf4j.query.algebra.Var;
 import org.eclipse.rdf4j.query.algebra.evaluation.EvaluationStrategy;
 import org.eclipse.rdf4j.query.algebra.evaluation.QueryValueEvaluationStep;
 import org.eclipse.rdf4j.query.algebra.evaluation.ValueExprEvaluationException;
 import org.eclipse.rdf4j.query.algebra.evaluation.impl.QueryEvaluationContext;
+import org.eclipse.rdf4j.query.algebra.helpers.AbstractQueryModelVisitor;
+import org.eclipse.rdf4j.query.algebra.helpers.collectors.VarNameCollector;
 
 @Deprecated(since = "4.1.0")
 public class FilterIterator extends FilterIteration<BindingSet, QueryEvaluationException> {
@@ -72,17 +78,49 @@ public static boolean isPartOfSubQuery(QueryModelNode node) {
 		}
 	}
 
+	protected static class VarCollector extends AbstractQueryModelVisitor<QueryEvaluationException> {
+
+		private final Set<String> collectedVars = new HashSet<>();
+
+		@Override
+		public void meet(Var var) {
+			if (!var.isAnonymous()) {
+				collectedVars.add(var.getName());
+			}
+		}
+
+		@Override
+		public void meet(BindingSetAssignment node) throws QueryEvaluationException {
+			for (BindingSet bs : node.getBindingSets()) {
+				for (String name : bs.getBindingNames()) {
+					collectedVars.add(name);
+				}
+			}
+			super.meet(node);
+		}
+
+		/**
+		 * @return Returns the collectedVars.
+		 */
+		public Set<String> getCollectedVars() {
+			return collectedVars;
+		}
+
+	}
+
 	/**
 	 * This is used to make sure that no variable is seen by the filter that are not in scope. Historically important in
-	 * subquery cases.
+	 * subquery cases. See also GH-4769
 	 */
 	public static final class RetainedVariableFilteredQueryEvaluationContext implements QueryEvaluationContext {
-		private final Filter node;
 		private final QueryEvaluationContext context;
+		private final Set<String> inScopeVariableNames;
 
 		public RetainedVariableFilteredQueryEvaluationContext(Filter node, QueryEvaluationContext contextToFilter) {
-			this.node = node;
 			this.context = contextToFilter;
+			final VarCollector varCollector = new VarCollector();
+			node.getArg().visit(varCollector);
+			this.inScopeVariableNames = varCollector.getCollectedVars();
 		}
 
 		@Override
@@ -105,7 +143,7 @@ public Predicate<BindingSet> hasBinding(String variableName) {
 		}
 
 		boolean isVariableInScope(String variableName) {
-			return node.getBindingNames().contains(variableName);
+			return inScopeVariableNames.contains(variableName);
 		}
 
 		@Override