Scripting: Add default implementation of close() for ScriptEngine (#24851)

Since groovy was removed, we no longer have any ScriptEngines with
resources to release. We may want to keep the option open for a script
engine to close resources, but this would not be common. This commit
adds a default implementation to ScriptEngine for `close()` to reduce
the boiler plate that must be added for a ScriptEngine implementation.

core/src/main/java/org/elasticsearch/script/ScriptEngine.java

@@ -23,6 +23,7 @@ import org.elasticsearch.common.Nullable;
 import org.elasticsearch.search.lookup.SearchLookup;
 
 import java.io.Closeable;
+import java.io.IOException;
 import java.util.Map;
 
 /**
@@ -47,4 +48,7 @@ public interface ScriptEngine extends Closeable {
     ExecutableScript executable(CompiledScript compiledScript, @Nullable Map<String, Object> vars);
 
     SearchScript search(CompiledScript compiledScript, SearchLookup lookup, @Nullable Map<String, Object> vars);
+
+    @Override
+    default void close() throws IOException {}
 }

core/src/test/java/org/elasticsearch/script/ScriptServiceTests.java

@@ -69,7 +69,6 @@ public class ScriptServiceTests extends ESTestCase {
         }
         scripts.put("script", p -> null);
         scriptEngine = new MockScriptEngine(Script.DEFAULT_SCRIPT_LANG, scripts);
-
         //prevent duplicates using map
         contexts = new HashMap<>(ScriptContext.BUILTINS);
         engines = new HashMap<>();
@@ -316,5 +315,4 @@ public class ScriptServiceTests extends ESTestCase {
                 notNullValue()
         );
     }
-
 }

core/src/test/java/org/elasticsearch/search/functionscore/ExplainableScriptIT.java

@@ -101,9 +101,6 @@ public class ExplainableScriptIT extends ESIntegTestCase {
                         }
                     };
                 }
-
-                @Override
-                public void close() {}
             };
         }
     }

core/src/test/java/org/elasticsearch/search/suggest/SuggestSearchIT.java

@@ -1021,10 +1021,6 @@ public class SuggestSearchIT extends ESIntegTestCase {
         // which makes the collate code thinks mustache is evaluating the query.
         public static final String NAME = "mustache";
 
-        @Override
-        public void close() throws IOException {
-        }
-
         @Override
         public String getType() {
             return NAME;

modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionScriptEngine.java

@@ -252,7 +252,4 @@ public class ExpressionScriptEngine extends AbstractComponent implements ScriptE
     public ExecutableScript executable(CompiledScript compiledScript, Map<String, Object> vars) {
         return new ExpressionExecutableScript(compiledScript, vars);
     }
-
-    @Override
-    public void close() {}
 }

modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/MustacheScriptEngine.java

@@ -97,11 +97,6 @@ public final class MustacheScriptEngine implements ScriptEngine {
         throw new UnsupportedOperationException();
     }
 
-    @Override
-    public void close() {
-        // Nothing to do here
-    }
-
     /**
      * Used at query execution time by script service in order to execute a query template.
      * */

modules/lang-painless/src/main/java/org/elasticsearch/painless/PainlessScriptEngine.java

@@ -211,14 +211,6 @@ public final class PainlessScriptEngine extends AbstractComponent implements Scr
         };
     }
 
-    /**
-     * Action taken when the engine is closed.
-     */
-    @Override
-    public void close() {
-        // Nothing to do.
-    }
-
     private ScriptException convertToScriptException(String scriptName, String scriptSource, Throwable t) {
         // create a script stack: this is just the script portion
         List<String> scriptStack = new ArrayList<>();

modules/lang-painless/src/test/java/org/elasticsearch/painless/NeedsScoreTests.java

@@ -60,7 +60,6 @@ public class NeedsScoreTests extends ESSingleNodeTestCase {
         ss = service.search(new CompiledScript(ScriptType.INLINE, "randomName", "painless", compiled),
                             lookup, Collections.<String, Object>emptyMap());
         assertTrue(ss.needsScores());
-        service.close();
     }
 
 }

plugins/examples/script-expert-scoring/src/main/java/org/elasticsearch/example/expertscript/ExpertScriptPlugin.java

@@ -134,7 +134,9 @@ public class ExpertScriptPlugin extends Plugin implements ScriptPlugin {
         }
 
         @Override
-        public void close() {}
+        public void close() {
+            // optionally close resources
+        }
     }
     // end::expert_engine
 }

test/framework/src/main/java/org/elasticsearch/script/MockScriptEngine.java

@@ -90,10 +90,6 @@ public class MockScriptEngine implements ScriptEngine {
         return compiled.createSearchScript(vars, lookup);
     }
 
-    @Override
-    public void close() throws IOException {
-    }
-
     public class MockCompiledScript {
 
         private final String name;