Let ListenableFuture implement thenable via a default interface metho…

…d in J2CL

RELNOTES=Let ListenableFuture implement thenable via a default interface method in J2CL

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=266186458

guava-gwt/pom.xml

@@ -54,6 +54,11 @@
       <artifactId>guava</artifactId>
       <version>${project.version}</version>
     </dependency>
+    <dependency>
+      <groupId>com.google.elemental2</groupId>
+      <artifactId>elemental2-promise</artifactId>
+      <version>1.0.0-RC1</version>
+    </dependency>
     <dependency>
       <groupId>com.google.guava</groupId>
       <artifactId>guava-testlib</artifactId>

guava-gwt/src-super/com/google/common/util/concurrent/super/com/google/common/util/concurrent/ListenableFuture.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2007 The Guava Authors
+ *
+ * Licensed 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 com.google.common.util.concurrent;
+
+import elemental2.promise.IThenable;
+import elemental2.promise.Promise;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Future;
+import jsinterop.annotations.JsMethod;
+
+/**
+ * Java super source for ListenableFuture, implementing a structural thenable via a default method.
+ * For restrictions, please refer to the documentation of the then() method.
+ *
+ * <p>This class is not (explicitly) implementing IThenable<V> because "then" is overloaded there
+ * and the single parameter version would need to be marked native, which does not seem to be
+ * feasible in interfaces (see "subclassing a class with overloaded methods" in jsinterop
+ * documentation).
+ */
+public interface ListenableFuture<V> extends Future<V> {
+  void addListener(Runnable listener, Executor executor);
+
+  /** Note that this method is not expected to be overridden. */
+  @JsMethod
+  default <R> Promise<R> then(
+      IThenable.ThenOnFulfilledCallbackFn<V, R> onFulfilled,
+      IThenable.ThenOnRejectedCallbackFn<R> onRejected) {
+    return new Promise<V>(
+            (resolve, reject) -> {
+              Futures.addCallback(
+                  this,
+                  new FutureCallback<V>() {
+                    @Override
+                    public void onSuccess(V value) {
+                      resolve.onInvoke(value);
+                    }
+
+                    @Override
+                    public void onFailure(Throwable throwable) {
+                      reject.onInvoke(throwable.getBackingJsObject());
+                    }
+                  },
+                  MoreExecutors.directExecutor());
+            })
+        .then(onFulfilled, onRejected);
+  }
+}

guava-gwt/src/com/google/common/util/concurrent/Concurrent.gwt.xml

@@ -17,6 +17,8 @@
   <inherits name="com.google.common.annotations.Annotations"/>
   <inherits name="com.google.common.base.Base"/>
   <inherits name="com.google.common.collect.Collect"/>
+  <inherits name="elemental2.promise.Promise"/>
+  <inherits name="jsinterop.base.Base"/>
   <inherits name="com.google.gwt.core.Core"/>
 
 </module>