Conditionalize Promise Polyfill for Hermes

Summary:
On Hermes, RN can directly use the Promise from global w/o the need of polyfilling it.

PromiseRejectionTrackingOptions are extracted to its own file so it can be shared by
both codepaths and preserve the behaviors that it's only imported on dev.
Some zero-overhead type gymnastics are used to flow-type it properly.

Changelog:
[General] - made promise polyfill conditionalized on Hermes

Reviewed By: cpojer

Differential Revision: D24068716

fbshipit-source-id: 3e0b1675493908324f27cc5b7300d8cc42a03acc

Libraries/Core/polyfillPromise.js

@@ -19,4 +19,20 @@ const {polyfillGlobal} = require('../Utilities/PolyfillFunctions');
  * If you don't need these polyfills, don't use InitializeCore; just directly
  * require the modules you need from InitializeCore for setup.
  */
-polyfillGlobal('Promise', () => require('../Promise'));
+
+// If global.Promise is provided by Hermes, we are confident that it can provide
+// all the methods needed by React Native, so we can directly use it.
+if (global?.HermesInternal?.hasPromise?.()) {
+  const HermesPromise = global.Promise;
+
+  if (__DEV__) {
+    if (typeof HermesPromise !== 'function') {
+      console.error('HermesPromise does not exist');
+    }
+    global.HermesInternal.enablePromiseRejectionTracker(
+      require('../promiseRejectionTrackingOptions').default,
+    );
+  }
+} else {
+  polyfillGlobal('Promise', () => require('../Promise'));
+}

Libraries/Promise.js

@@ -16,42 +16,9 @@ require('promise/setimmediate/done');
 require('promise/setimmediate/finally');
 
 if (__DEV__) {
-  require('promise/setimmediate/rejection-tracking').enable({
-    allRejections: true,
-    onUnhandled: (id, rejection = {}) => {
-      let message: string;
-      let stack: ?string;
-
-      const stringValue = Object.prototype.toString.call(rejection);
-      if (stringValue === '[object Error]') {
-        message = Error.prototype.toString.call(rejection);
-        const error: Error = (rejection: $FlowFixMe);
-        stack = error.stack;
-      } else {
-        try {
-          message = require('pretty-format')(rejection);
-        } catch {
-          message =
-            typeof rejection === 'string'
-              ? rejection
-              : JSON.stringify((rejection: $FlowFixMe));
-        }
-      }
-
-      const warning =
-        `Possible Unhandled Promise Rejection (id: ${id}):\n` +
-        `${message ?? ''}\n` +
-        (stack == null ? '' : stack);
-      console.warn(warning);
-    },
-    onHandled: id => {
-      const warning =
-        `Promise Rejection Handled (id: ${id})\n` +
-        'This means you can ignore any previous messages of the form ' +
-        `"Possible Unhandled Promise Rejection (id: ${id}):"`;
-      console.warn(warning);
-    },
-  });
+  require('promise/setimmediate/rejection-tracking').enable(
+    require('./promiseRejectionTrackingOptions').default,
+  );
 }
 
 module.exports = Promise;

Libraries/promiseRejectionTrackingOptions.js

@@ -0,0 +1,54 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @flow strict
+ */
+
+'use strict';
+
+import typeof {enable} from 'promise/setimmediate/rejection-tracking';
+
+type ExtractOptionsType = <P>((options?: ?P) => void) => P;
+
+let rejectionTrackingOptions: $Call<ExtractOptionsType, enable> = {
+  allRejections: true,
+  onUnhandled: (id, rejection = {}) => {
+    let message: string;
+    let stack: ?string;
+
+    const stringValue = Object.prototype.toString.call(rejection);
+    if (stringValue === '[object Error]') {
+      message = Error.prototype.toString.call(rejection);
+      const error: Error = (rejection: $FlowFixMe);
+      stack = error.stack;
+    } else {
+      try {
+        message = require('pretty-format')(rejection);
+      } catch {
+        message =
+          typeof rejection === 'string'
+            ? rejection
+            : JSON.stringify((rejection: $FlowFixMe));
+      }
+    }
+
+    const warning =
+      `Possible Unhandled Promise Rejection (id: ${id}):\n` +
+      `${message ?? ''}\n` +
+      (stack == null ? '' : stack);
+    console.warn(warning);
+  },
+  onHandled: id => {
+    const warning =
+      `Promise Rejection Handled (id: ${id})\n` +
+      'This means you can ignore any previous messages of the form ' +
+      `"Possible Unhandled Promise Rejection (id: ${id}):"`;
+    console.warn(warning);
+  },
+};
+
+export default rejectionTrackingOptions;