Add LogicalPlanOptimizer test

Author: alex-spies

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizerTests.java

@@ -41,6 +41,7 @@
 import org.elasticsearch.xpack.esql.core.expression.predicate.logical.Or;
 import org.elasticsearch.xpack.esql.core.expression.predicate.nulls.IsNotNull;
 import org.elasticsearch.xpack.esql.core.expression.predicate.operator.comparison.BinaryComparison;
+import org.elasticsearch.xpack.esql.core.tree.Source;
 import org.elasticsearch.xpack.esql.core.type.DataType;
 import org.elasticsearch.xpack.esql.core.type.EsField;
 import org.elasticsearch.xpack.esql.core.util.Holder;
@@ -113,7 +114,9 @@
 import org.elasticsearch.xpack.esql.plan.logical.UnaryPlan;
 import org.elasticsearch.xpack.esql.plan.logical.join.InlineJoin;
 import org.elasticsearch.xpack.esql.plan.logical.join.Join;
+import org.elasticsearch.xpack.esql.plan.logical.join.JoinConfig;
 import org.elasticsearch.xpack.esql.plan.logical.join.JoinTypes;
+import org.elasticsearch.xpack.esql.plan.logical.join.LookupJoin;
 import org.elasticsearch.xpack.esql.plan.logical.local.EsqlProject;
 import org.elasticsearch.xpack.esql.plan.logical.local.LocalRelation;
 import org.elasticsearch.xpack.esql.plan.logical.local.LocalSupplier;
@@ -139,6 +142,7 @@
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.TWO;
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.as;
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.emptySource;
+import static org.elasticsearch.xpack.esql.EsqlTestUtils.fieldAttribute;
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.getFieldAttribute;
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.loadMapping;
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.localSource;
@@ -1294,6 +1298,29 @@ public void testCombineLimits() {
         );
     }
 
+    public void testPushdownLimitsPastLeftJoin() {
+        var leftChild = emptySource();
+        var rightChild = new LocalRelation(Source.EMPTY, List.of(fieldAttribute()), LocalSupplier.EMPTY);;
+        assertNotEquals(leftChild, rightChild);
+
+        var joinConfig = new JoinConfig(JoinTypes.LEFT, List.of(), List.of(), List.of());
+        var join = switch (randomIntBetween(0, 2)) {
+            case 0 -> new Join(EMPTY, leftChild, rightChild, joinConfig);
+            case 1 -> new LookupJoin(EMPTY, leftChild, rightChild, joinConfig);
+            case 2 -> new InlineJoin(EMPTY, leftChild, rightChild, joinConfig);
+            default -> throw new IllegalArgumentException();
+        };
+
+        var limit = new Limit(EMPTY, L(10), join);
+
+        var optimizedPlan = new PushDownAndCombineLimits().rule(limit);
+
+        assertEquals(
+            join.replaceChildren(limit.replaceChild(join.left()), join.right()),
+            optimizedPlan
+        );
+    }
+
     public void testMultipleCombineLimits() {
         var numberOfLimits = randomIntBetween(3, 10);
         var minimum = randomIntBetween(10, 99);