ESQL: Lock testing to LEFT joins only (#110165)

We only support LEFT joins at the moment and the tests would randomly
fail.

Closes #110158 Closes #110152

x-pack/plugin/esql-core/src/main/java/org/elasticsearch/xpack/esql/core/expression/function/FunctionRegistry.java

@@ -390,7 +390,7 @@ public class FunctionRegistry {
      * Build a {@linkplain FunctionDefinition} for a one-argument function that is configuration aware.
      */
     @SuppressWarnings("overloads")
-    protected static <T extends Function> FunctionDefinition def(
+    public static <T extends Function> FunctionDefinition def(
         Class<T> function,
         UnaryConfigurationAwareBuilder<T> ctorRef,
         String... names
@@ -405,7 +405,7 @@ public class FunctionRegistry {
         return def(function, builder, names);
     }
 
-    protected interface UnaryConfigurationAwareBuilder<T> {
+    public interface UnaryConfigurationAwareBuilder<T> {
         T build(Source source, Expression exp, Configuration configuration);
     }
 

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistryTests.java

@@ -7,6 +7,7 @@
 
 package org.elasticsearch.xpack.esql.expression.function;
 
+import org.elasticsearch.compute.operator.EvalOperator;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.xpack.esql.core.ParsingException;
 import org.elasticsearch.xpack.esql.core.QlIllegalArgumentException;
@@ -15,11 +16,18 @@ import org.elasticsearch.xpack.esql.core.expression.function.FunctionDefinition;
 import org.elasticsearch.xpack.esql.core.expression.function.FunctionRegistry;
 import org.elasticsearch.xpack.esql.core.expression.function.FunctionRegistryTests;
 import org.elasticsearch.xpack.esql.core.expression.function.FunctionResolutionStrategy;
+import org.elasticsearch.xpack.esql.core.expression.function.OptionalArgument;
 import org.elasticsearch.xpack.esql.core.expression.function.UnresolvedFunction;
+import org.elasticsearch.xpack.esql.core.session.Configuration;
+import org.elasticsearch.xpack.esql.core.tree.NodeInfo;
 import org.elasticsearch.xpack.esql.core.tree.Source;
 import org.elasticsearch.xpack.esql.core.tree.SourceTests;
+import org.elasticsearch.xpack.esql.core.type.DataType;
+import org.elasticsearch.xpack.esql.expression.function.scalar.EsqlConfigurationFunction;
 
 import java.util.Arrays;
+import java.util.List;
+import java.util.function.Function;
 
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.randomConfiguration;
 import static org.elasticsearch.xpack.esql.core.expression.function.FunctionRegistry.def;
@@ -78,6 +86,19 @@ public class EsqlFunctionRegistryTests extends ESTestCase {
         assertThat(e.getMessage(), endsWith("expects exactly one argument"));
     }
 
+    public void testConfigurationOptionalFunction() {
+        UnresolvedFunction ur = uf(DEFAULT, mock(Expression.class));
+        FunctionDefinition def;
+        FunctionRegistry r = new EsqlFunctionRegistry(
+            EsqlFunctionRegistry.def(DummyConfigurationOptionalArgumentFunction.class, (Source l, Expression e, Configuration c) -> {
+                assertSame(e, ur.children().get(0));
+                return new DummyConfigurationOptionalArgumentFunction(l, List.of(ur), c);
+            }, "dummy")
+        );
+        def = r.resolveFunction(r.resolveAlias("DUMMY"));
+        assertEquals(ur.source(), ur.buildResolved(randomConfiguration(), def).source());
+    }
+
     private static UnresolvedFunction uf(FunctionResolutionStrategy resolutionStrategy, Expression... children) {
         return new UnresolvedFunction(SourceTests.randomSource(), "dummyFunction", resolutionStrategy, Arrays.asList(children));
     }
@@ -104,4 +125,33 @@ public class EsqlFunctionRegistryTests extends ESTestCase {
         }
         return output.toString();
     }
+
+    public static class DummyConfigurationOptionalArgumentFunction extends EsqlConfigurationFunction implements OptionalArgument {
+
+        public DummyConfigurationOptionalArgumentFunction(Source source, List<Expression> fields, Configuration configuration) {
+            super(source, fields, configuration);
+        }
+
+        @Override
+        public DataType dataType() {
+            return null;
+        }
+
+        @Override
+        public Expression replaceChildren(List<Expression> newChildren) {
+            return new DummyConfigurationOptionalArgumentFunction(source(), newChildren, configuration());
+        }
+
+        @Override
+        protected NodeInfo<? extends Expression> info() {
+            return NodeInfo.create(this, DummyConfigurationOptionalArgumentFunction::new, children(), configuration());
+        }
+
+        @Override
+        public EvalOperator.ExpressionEvaluator.Factory toEvaluator(
+            Function<Expression, EvalOperator.ExpressionEvaluator.Factory> toEvaluator
+        ) {
+            return null;
+        }
+    }
 }

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/tree/EsqlNodeSubclassTests.java

@@ -88,7 +88,7 @@ public class EsqlNodeSubclassTests<T extends B, B extends Node<B>> extends NodeS
             return randomInt();
         } else if (argClass == JoinConfig.class) {
             return new JoinConfig(
-                randomFrom(JoinType.values()),
+                JoinType.LEFT,
                 randomList(0, 10, () -> (Attribute) makeArg(Attribute.class)),
                 randomList(0, 10, () -> (Expression) makeArg(Expression.class))
             );