fix: Cypher -> allReduce(...) may evaluate true cases as false

Fixed issue #4043

The predicate is now only evaluated inside each iteration where the iterator variable is bound. Empty lists yield vacuous true, matching Neo4j/Cypher 25 semantics.

Author: lvca

engine/src/main/java/com/arcadedb/query/opencypher/ast/AllReduceExpression.java

@@ -82,13 +82,9 @@ else if (listValue.getClass().isArray())
     else
       throw new IllegalArgumentException("allReduce() requires a list, got: " + listValue.getClass().getSimpleName());
 
-    // Check initial accumulator against predicate
-    final ResultInternal initResult = createIterationResult(result, null, accumulator);
-    final Object initCheck = OpenCypherQueryEngine.getExpressionEvaluator().evaluate(predicateExpression, initResult, context);
-    if (!Boolean.TRUE.equals(initCheck))
-      return false;
-
-    // Iterate over each element, updating the accumulator and checking the predicate
+    // Iterate over each element, updating the accumulator and checking the predicate.
+    // The predicate is only evaluated within each iteration where the iterator variable is bound;
+    // an empty list yields vacuous truth (true). Matches Neo4j/Cypher 25 semantics.
     for (final Object item : iterable) {
       final ResultInternal iterResult = createIterationResult(result, item, accumulator);
 

engine/src/test/java/com/arcadedb/query/opencypher/CypherBuiltInFunctionsTest.java

@@ -1385,6 +1385,33 @@ void allReducePredicateFails() {
     });
   }
 
+  @Test
+  void issue4043_allReducePredicateOnIteratorVariable() {
+    // Issue #4043: predicate referencing the iterator variable returned false even
+    // when every element satisfied it. Neo4j returns true for all three queries below.
+    database.transaction(() -> {
+      ResultSet rs = database.query("opencypher",
+          "RETURN allReduce(acc = 0, x IN [1, 2, 3] | acc + x, x > 0) AS result");
+      assertThat(rs.hasNext()).isTrue();
+      assertThat((boolean) rs.next().getProperty("result")).isTrue();
+
+      rs = database.query("opencypher",
+          "RETURN allReduce(acc = 0, x IN [1, 2, 3] | acc + x, x > 10) AS result");
+      assertThat(rs.hasNext()).isTrue();
+      assertThat((boolean) rs.next().getProperty("result")).isFalse();
+
+      rs = database.query("opencypher",
+          "RETURN allReduce(acc = 0, x IN [] | acc + x, x > 0) AS result");
+      assertThat(rs.hasNext()).isTrue();
+      assertThat((boolean) rs.next().getProperty("result")).isTrue();
+
+      rs = database.query("opencypher",
+          "RETURN allReduce(acc = 0, x IN [1, 2, 3] | acc + x, acc >= 0) AS result");
+      assertThat(rs.hasNext()).isTrue();
+      assertThat((boolean) rs.next().getProperty("result")).isTrue();
+    });
+  }
+
   // Note: Integration tests for Cypher queries with built-in functions
   // should be placed in a test class that has access to the Cypher query engine.
   // The tests above verify the function implementations directly.