Uses findMetroConfig and fetchMetroConfig in the internal RN cli

Reviewed By: davidaurelio

Differential Revision: D6819226

fbshipit-source-id: 6436855cc5dce9ce7922d89df99c3cb90abb095e

packages/metro/src/cli-utils.js

@@ -12,6 +12,8 @@
 
 'use strict';
 
+const Config = require('./Config');
+
 const fs = require('fs-extra');
 const path = require('path');
 
@@ -19,6 +21,11 @@ import type {ConfigT} from './Config';
 
 const METRO_CONFIG_FILENAME = 'metro.config.js';
 
+type MetroConfigSearchOptions = {|
+  cwd?: string,
+  basename?: string,
+|};
+
 exports.watchFile = async function(
   filename: string,
   callback: () => *,
@@ -30,15 +37,21 @@ exports.watchFile = async function(
   await callback();
 };
 
-exports.findMetroConfig = async function(filename: ?string): Promise<?string> {
+exports.findMetroConfig = async function(
+  filename: ?string,
+  {
+    cwd = process.cwd(),
+    basename = METRO_CONFIG_FILENAME,
+  }: MetroConfigSearchOptions = {},
+): Promise<?string> {
   if (filename) {
-    return path.resolve(process.cwd(), filename);
+    return path.resolve(cwd, filename);
   } else {
     let previous;
-    let current = process.cwd();
+    let current = cwd;
 
     do {
-      const filename = path.join(current, METRO_CONFIG_FILENAME);
+      const filename = path.join(current, basename);
 
       if (fs.existsSync(filename)) {
         return filename;
@@ -54,14 +67,16 @@ exports.findMetroConfig = async function(filename: ?string): Promise<?string> {
 
 exports.fetchMetroConfig = async function(
   filename: ?string,
-): Promise<$Shape<ConfigT>> {
-  const location = await exports.findMetroConfig(filename);
-  if (location) {
-    // $FlowFixMe: We want this require to be dynamic
-    return require(location);
-  } else {
-    return {};
-  }
+  // $FlowFixMe: This is a known Flow issue where it doesn't detect that an empty object is a valid value for a strict shape where all the members are optionals
+  searchOptions: MetroConfigSearchOptions = {},
+): Promise<ConfigT> {
+  const location = await exports.findMetroConfig(filename, searchOptions);
+
+  // $FlowFixMe: We want this require to be dynamic
+  const config = location ? require(location) : null;
+
+  // $FlowFixMe: For some reason, Flow doesn't recognize the return value as a promise
+  return config ? Config.normalize(config) : Config.DEFAULT;
 };
 
 // eslint-disable-next-line no-unclear-flowtypes