Convert MSQTerminalStageSpecFactory into an interface (apache#16996)

* Convert MSQTerminalStageSpecFactory into an interface

* Rename class and remove useless constructor

extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/guice/MSQSqlModule.java

@@ -54,7 +54,7 @@ public void configure(Binder binder)
     // We want this module to bring InputSourceModule along for the ride.
     binder.install(new InputSourceModule());
 
-    binder.bind(MSQTerminalStageSpecFactory.class).toInstance(new MSQTerminalStageSpecFactory());
+    binder.bind(MSQTerminalStageSpecFactory.class).to(SegmentGenerationTerminalStageSpecFactory.class).in(LazySingleton.class);
 
     binder.bind(MSQTaskSqlEngine.class).in(LazySingleton.class);
 

extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/guice/MSQTerminalStageSpecFactory.java

@@ -19,19 +19,14 @@
 
 package org.apache.druid.msq.guice;
 
-import org.apache.druid.msq.indexing.destination.SegmentGenerationStageSpec;
 import org.apache.druid.msq.indexing.destination.TerminalStageSpec;
 import org.apache.druid.sql.calcite.planner.PlannerContext;
 import org.apache.druid.sql.calcite.rel.DruidQuery;
 
-public class MSQTerminalStageSpecFactory
+public interface MSQTerminalStageSpecFactory
 {
   /**
-   * Creates a {@link TerminalStageSpec} which determines the final of a query. Currently, always returns a segment
-   * generation spec, but this can be used to configure a wide range of behaviours.
+   * Creates a {@link TerminalStageSpec} which determines the final of a query.
    */
-  public TerminalStageSpec createTerminalStageSpec(DruidQuery druidQuery, PlannerContext plannerContext)
-  {
-    return SegmentGenerationStageSpec.instance();
-  }
+  TerminalStageSpec createTerminalStageSpec(DruidQuery druidQuery, PlannerContext plannerContext);
 }

extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/guice/SegmentGenerationTerminalStageSpecFactory.java

@@ -0,0 +1,37 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.msq.guice;
+
+import org.apache.druid.msq.indexing.destination.SegmentGenerationStageSpec;
+import org.apache.druid.msq.indexing.destination.TerminalStageSpec;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.rel.DruidQuery;
+
+/**
+ * Configures ingestion queries to create new segments with the results in all cases.
+ */
+public class SegmentGenerationTerminalStageSpecFactory implements MSQTerminalStageSpecFactory
+{
+  @Override
+  public TerminalStageSpec createTerminalStageSpec(DruidQuery druidQuery, PlannerContext plannerContext)
+  {
+    return SegmentGenerationStageSpec.instance();
+  }
+}

extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/sql/MSQTaskSqlEngine.java

@@ -20,7 +20,6 @@
 package org.apache.druid.msq.sql;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
-import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.inject.Inject;
@@ -90,12 +89,6 @@ public class MSQTaskSqlEngine implements SqlEngine
   private final MSQTerminalStageSpecFactory terminalStageSpecFactory;
 
   @Inject
-  public MSQTaskSqlEngine(final OverlordClient overlordClient, final ObjectMapper jsonMapper)
-  {
-    this(overlordClient, jsonMapper, new MSQTerminalStageSpecFactory());
-  }
-
-  @VisibleForTesting
   public MSQTaskSqlEngine(
       final OverlordClient overlordClient,
       final ObjectMapper jsonMapper,

extensions-core/multi-stage-query/src/test/java/org/apache/druid/msq/exec/TestMSQSqlModule.java

@@ -26,6 +26,7 @@
 import org.apache.druid.guice.LazySingleton;
 import org.apache.druid.initialization.ServerInjectorBuilderTest.TestDruidModule;
 import org.apache.druid.msq.guice.MultiStageQuery;
+import org.apache.druid.msq.guice.SegmentGenerationTerminalStageSpecFactory;
 import org.apache.druid.msq.sql.MSQTaskSqlEngine;
 import org.apache.druid.msq.test.MSQTestBase;
 import org.apache.druid.msq.test.MSQTestOverlordServiceClient;
@@ -53,7 +54,7 @@ public MSQTaskSqlEngine createEngine(
       ObjectMapper queryJsonMapper,
       MSQTestOverlordServiceClient indexingServiceClient)
   {
-    return new MSQTaskSqlEngine(indexingServiceClient, queryJsonMapper);
+    return new MSQTaskSqlEngine(indexingServiceClient, queryJsonMapper, new SegmentGenerationTerminalStageSpecFactory());
   }
 
   @Provides

extensions-core/multi-stage-query/src/test/java/org/apache/druid/msq/test/MSQTestBase.java

@@ -91,8 +91,8 @@
 import org.apache.druid.msq.guice.MSQExternalDataSourceModule;
 import org.apache.druid.msq.guice.MSQIndexingModule;
 import org.apache.druid.msq.guice.MSQSqlModule;
-import org.apache.druid.msq.guice.MSQTerminalStageSpecFactory;
 import org.apache.druid.msq.guice.MultiStageQuery;
+import org.apache.druid.msq.guice.SegmentGenerationTerminalStageSpecFactory;
 import org.apache.druid.msq.indexing.InputChannelFactory;
 import org.apache.druid.msq.indexing.MSQControllerTask;
 import org.apache.druid.msq.indexing.MSQSpec;
@@ -551,7 +551,7 @@ public String getFormatString()
     final SqlEngine engine = new MSQTaskSqlEngine(
         indexingServiceClient,
         qf.queryJsonMapper().copy().registerModules(new MSQSqlModule().getJacksonModules()),
-        new MSQTerminalStageSpecFactory()
+        new SegmentGenerationTerminalStageSpecFactory()
     );
 
     PlannerFactory plannerFactory = new PlannerFactory(