Make reindex and lang-javascript compatible

Fixes two issues:
1. lang-javascript doesn't support `executable` with a `null` `vars`
parameters. The parameter is quite nullable.
2. reindex didn't support script engines who's `unwrap` method wasn't
a noop. This didn't come up for lang-groovy or lang-painless because
both of those `unwrap`s were noops. lang-javascript copys all maps that
it `unwrap`s.

This adds fairly low level unit tests for these fixes but dosen't add
an integration test that makes sure that reindex and lang-javascript
play well together. That'd make backporting this difficult and would
add a fairly significant amount of time to the build for a fairly rare
interaction. Hopefully the unit tests will be enough.

modules/reindex/src/main/java/org/elasticsearch/index/reindex/AbstractAsyncBulkIndexByScrollAction.java

@@ -450,6 +450,8 @@ public RequestWrapper<?> apply(RequestWrapper<?> request, ScrollableHitSource.Hi
             }
             if (context == null) {
                 context = new HashMap<>();
+            } else {
+                context.clear();
             }
 
             context.put(IndexFieldMapper.NAME, doc.getIndex());
@@ -485,50 +487,50 @@ public RequestWrapper<?> apply(RequestWrapper<?> request, ScrollableHitSource.Hi
              */
             request.setSource((Map<String, Object>) resultCtx.remove(SourceFieldMapper.NAME));
 
-            Object newValue = context.remove(IndexFieldMapper.NAME);
+            Object newValue = resultCtx.remove(IndexFieldMapper.NAME);
             if (false == doc.getIndex().equals(newValue)) {
                 scriptChangedIndex(request, newValue);
             }
-            newValue = context.remove(TypeFieldMapper.NAME);
+            newValue = resultCtx.remove(TypeFieldMapper.NAME);
             if (false == doc.getType().equals(newValue)) {
                 scriptChangedType(request, newValue);
             }
-            newValue = context.remove(IdFieldMapper.NAME);
+            newValue = resultCtx.remove(IdFieldMapper.NAME);
             if (false == doc.getId().equals(newValue)) {
                 scriptChangedId(request, newValue);
             }
-            newValue = context.remove(VersionFieldMapper.NAME);
+            newValue = resultCtx.remove(VersionFieldMapper.NAME);
             if (false == Objects.equals(oldVersion, newValue)) {
                 scriptChangedVersion(request, newValue);
             }
-            newValue = context.remove(ParentFieldMapper.NAME);
+            newValue = resultCtx.remove(ParentFieldMapper.NAME);
             if (false == Objects.equals(oldParent, newValue)) {
                 scriptChangedParent(request, newValue);
             }
             /*
              * Its important that routing comes after parent in case you want to
              * change them both.
              */
-            newValue = context.remove(RoutingFieldMapper.NAME);
+            newValue = resultCtx.remove(RoutingFieldMapper.NAME);
             if (false == Objects.equals(oldRouting, newValue)) {
                 scriptChangedRouting(request, newValue);
             }
-            newValue = context.remove(TimestampFieldMapper.NAME);
+            newValue = resultCtx.remove(TimestampFieldMapper.NAME);
             if (false == Objects.equals(oldTimestamp, newValue)) {
                 scriptChangedTimestamp(request, newValue);
             }
-            newValue = context.remove(TTLFieldMapper.NAME);
+            newValue = resultCtx.remove(TTLFieldMapper.NAME);
             if (false == Objects.equals(oldTTL, newValue)) {
                 scriptChangedTTL(request, newValue);
             }
 
             OpType newOpType = OpType.fromString(newOp);
-            if (newOpType !=  oldOpType) {
+            if (newOpType != oldOpType) {
                 return scriptChangedOpType(request, oldOpType, newOpType);
             }
 
-            if (false == context.isEmpty()) {
-                throw new IllegalArgumentException("Invalid fields added to context [" + String.join(",", context.keySet()) + ']');
+            if (false == resultCtx.isEmpty()) {
+                throw new IllegalArgumentException("Invalid fields added to context [" + String.join(",", resultCtx.keySet()) + ']');
             }
             return request;
         }

modules/reindex/src/test/java/org/elasticsearch/index/reindex/SimpleExecutableScript.java

@@ -21,9 +21,12 @@
 
 import org.elasticsearch.script.ExecutableScript;
 
+import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Consumer;
 
+import static org.elasticsearch.test.ESTestCase.randomBoolean;
+
 public class SimpleExecutableScript implements ExecutableScript {
     private final Consumer<Map<String, Object>> script;
     private Map<String, Object> ctx;
@@ -50,6 +53,13 @@ public void setNextVar(String name, Object value) {
 
     @Override
     public Object unwrap(Object value) {
+        // Some script engines (javascript) copy any maps they unwrap
+        if (randomBoolean()) {
+            if (value instanceof Map) {
+                return new HashMap<>((Map<?, ?>) value);
+            }
+        }
+        // Others just return the objects plain (groovy, painless)
         return value;
     }
 }

plugins/lang-javascript/src/main/java/org/elasticsearch/script/javascript/JavaScriptScriptEngineService.java

@@ -172,14 +172,16 @@ public Object compile(String scriptName, String scriptSource, Map<String, String
     }
 
     @Override
-    public ExecutableScript executable(CompiledScript compiledScript, Map<String, Object> vars) {
+    public ExecutableScript executable(CompiledScript compiledScript, @Nullable Map<String, Object> vars) {
         Context ctx = Context.enter();
         try {
             Scriptable scope = ctx.newObject(globalScope);
             scope.setPrototype(globalScope);
             scope.setParentScope(null);
-            for (Map.Entry<String, Object> entry : vars.entrySet()) {
-                ScriptableObject.putProperty(scope, entry.getKey(), entry.getValue());
+            if (vars != null) {
+                for (Map.Entry<String, Object> entry : vars.entrySet()) {
+                    ScriptableObject.putProperty(scope, entry.getKey(), entry.getValue());
+                }
             }
 
             return new JavaScriptExecutableScript((Script) compiledScript.compiled(), scope);

plugins/lang-javascript/src/test/java/org/elasticsearch/script/javascript/JavaScriptScriptEngineTests.java

@@ -25,6 +25,8 @@
 import java.util.List;
 import java.util.Map;
 
+import static java.util.Collections.emptyMap;
+
 import org.elasticsearch.common.collect.MapBuilder;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.script.CompiledScript;
@@ -59,6 +61,13 @@ public void testSimpleEquation() {
         assertThat(((Number) o).intValue(), equalTo(3));
     }
 
+    public void testNullVars() {
+        CompiledScript script = new CompiledScript(ScriptService.ScriptType.INLINE, "testSimpleEquation", "js",
+                se.compile(null, "1 + 2", emptyMap()));
+        Object o = se.executable(script, null).run();
+        assertThat(((Number) o).intValue(), equalTo(3));
+    }
+
     @SuppressWarnings("unchecked")
     public void testMapAccess() {
         Map<String, Object> vars = new HashMap<String, Object>();