packager: add utilities to log errors internally

Reviewed By: davidaurelio

Differential Revision: D4468471

fbshipit-source-id: 10deb5014d06e4d3bb9d3122eef362c09f74d044

packages/metro-bundler/react-packager/src/lib/__mocks__/BatchProcessor.js

@@ -0,0 +1,41 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+'use strict';
+
+const {EventEmitter} = require('events');
+
+class BatchProcessorMock {
+
+  constructor(_, processBatch) {
+    this._processBatch = processBatch;
+    this._queue = [];
+    BatchProcessorMock.mocks.emit('new', this);
+  }
+
+  queue(item, callback) {
+    this._queue.push([item, callback]);
+  }
+
+  flush(callback) {
+    const {_queue} = this;
+    this._queue = [];
+    process.nextTick(() => {
+      this._processBatch(_queue.map(pair => pair[0]), (error, res) => {
+        _queue.forEach((pair, i) => pair[1](error, res && res[i]));
+        callback();
+      });
+    });
+  }
+
+}
+
+BatchProcessorMock.mocks = new EventEmitter();
+
+module.exports = BatchProcessorMock;

packages/metro-bundler/react-packager/src/lib/reporting.js

@@ -84,6 +84,14 @@ function logWarning(terminal: Terminal, format: string, ...args: Array<mixed>):
   terminal.log('%s: %s', chalk.yellow('warning'), str);
 }
 
+/**
+ * Similar to `logWarning`, but for messages that require the user to act.
+ */
+function logError(terminal: Terminal, format: string, ...args: Array<mixed>): void {
+  const str = util.format(format, ...args);
+  terminal.log('%s: %s', chalk.red('error'), str);
+}
+
 /**
  * A reporter that does nothing. Errors and warnings will be swallowed, that
  * is generally not what you want.
@@ -92,5 +100,6 @@ const nullReporter = {update() {}};
 
 module.exports = {
   logWarning,
+  logError,
   nullReporter,
 };