promise: hard deprecation for unhandled promise rejection

PR-URL: https://github.com/nodejs/node/pull/8217
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

lib/internal/process/promises.js

@@ -45,6 +45,7 @@ function setupPromises(scheduleMicrotasks) {
     }
   }
 
+  var deprecationWarned = false;
   function emitPendingUnhandledRejections() {
     let hadListeners = false;
     while (pendingUnhandledRejections.length > 0) {
@@ -59,6 +60,14 @@ function setupPromises(scheduleMicrotasks) {
           warning.name = 'UnhandledPromiseRejectionWarning';
           warning.id = uid;
           process.emitWarning(warning);
+          if (!deprecationWarned) {
+            deprecationWarned = true;
+            process.emitWarning(
+              'Unhandled promise rejections are deprecated. In the future, ' +
+              'promise rejections that are not handled will terminate the ' +
+              'Node.js process with a non-zero exit code.',
+              'DeprecationWarning');
+          }
         } else {
           hadListeners = true;
         }

test/parallel/test-promises-warning-on-unhandled-rejection.js

@@ -16,11 +16,14 @@ process.on('warning', common.mustCall((warning) => {
       assert(/Unhandled promise rejection/.test(warning.message));
       break;
     case 1:
+      assert.strictEqual(warning.name, 'DeprecationWarning');
+      break;
+    case 2:
       assert.strictEqual(warning.name, 'PromiseRejectionHandledWarning');
       assert(/Promise rejection was handled asynchronously/
         .test(warning.message));
   }
-}, 2));
+}, 3));
 
 const p = Promise.reject('This was rejected');
 setImmediate(common.mustCall(() => p.catch(() => {})));