Stop using projectRoots from RN cli

Summary:
This diff tries to fix an issue that started appearing in RN master when the latest metro version is used (more info here: c5ce762#commitcomment-29443117).

The problem is that RN is still reading `projectRoots` from the Metro config and trying to call `concat()` on them. Latest Metro sets the default `projectRoots` to null, so this fails.

Also, a couple other things have been done:

* Make sure that the `projectRoot` and `watchFolder` objects from args are passed to Metro (so they contain the overrides from the CLI arguments).
* Add a `--projectRoot` CLI arg, replacing the `--root` one (this is not actually needed, since it does the same as `--watchFolders`

Differential Revision: D8567229

fbshipit-source-id: 3b76fd8e23d201a4097e9dfba3a512d64f348cb0

Author: rafeca

local-cli/server/runServer.js

@@ -56,7 +56,7 @@ export type Args = {|
   +nonPersistent: boolean,
   +platforms: $ReadOnlyArray<string>,
   +port: number,
-  +projectRoots: $ReadOnlyArray<string>,
+  +projectRoot: string,
   +resetCache: boolean,
   +sourceExts: $ReadOnlyArray<string>,
   +verbose: boolean,
@@ -197,7 +197,7 @@ function getPackagerServer(args, config, reporter) {
     polyfillModuleNames: config.getPolyfillModuleNames(),
     postMinifyProcess: config.postMinifyProcess,
     postProcessBundleSourcemap: config.postProcessBundleSourcemap,
-    projectRoot: config.getProjectRoot(),
+    projectRoot: args.projectRoot,
     providesModuleNodeModules: providesModuleNodeModules,
     reporter,
     resetCache: args.resetCache,
@@ -206,7 +206,7 @@ function getPackagerServer(args, config, reporter) {
     transformModulePath: transformModulePath,
     verbose: args.verbose,
     watch: !args.nonPersistent,
-    watchFolders: config.getWatchFolders(),
+    watchFolders: args.watchFolders,
     workerPath: config.getWorkerPath(),
   });
 }

local-cli/server/server.js

@@ -10,7 +10,6 @@
 
 'use strict';
 
-const path = require('path');
 const runServer = require('./runServer');
 
 import type {RNConfig} from '../core';
@@ -20,15 +19,12 @@ import type {Args as RunServerArgs} from './runServer';
 /**
  * Starts the React Native Packager Server.
  */
-function server(argv: mixed, config: RNConfig, allArgs: Object) {
-  const {root, ...args} = allArgs;
-  args.projectRoots = args.projectRoots.concat(root);
-
+function server(argv: mixed, config: RNConfig, args: Object) {
   const startedCallback = logReporter => {
     logReporter.update({
       type: 'initialize_started',
       port: args.port,
-      projectRoots: args.projectRoots,
+      projectRoots: args.watchFolders,
     });
 
     process.on('uncaughtException', error => {
@@ -68,19 +64,19 @@ module.exports = {
       default: '',
     },
     {
-      command: '--root [list]',
-      description:
-        'add another root(s) to be used by the packager in this project',
-      parse: (val: string) => val.split(',').map(root => path.resolve(root)),
-      default: [],
+      command: '--projectRoot [string]',
+      description: 'Specify the main project root',
+      default: (config: ConfigT) => {
+        return config.getProjectRoot();
+      },
     },
     {
       command: '--watchFolders [list]',
       description:
-        'Sepcify any additional folders to be added to the watch list',
+        'Specify any additional folders to be added to the watch list',
       parse: (val: string) => val.split(','),
       default: (config: ConfigT) => {
-        return config.getProjectRoots ? config.getProjectRoots() : undefined;
+        return config.getWatchFolders();
       },
     },
     {