Make config object read-only

Summary: This makes the Metro config type readonly, only a couple of things inside Metro needed to be tweaked :)

Reviewed By: mjesun

Differential Revision: D10028083

fbshipit-source-id: 15f5d957a8ee7384d6156c973639d86240fd251f

local-cli/core/index.js

@@ -131,12 +131,16 @@ async function getCliConfig(): Promise<RNConfig> {
     cliArgs.config != null ? path.resolve(__dirname, cliArgs.config) : null,
   );
 
+  // $FlowFixMe Metro configuration is immutable.
   config.transformer.assetRegistryPath = ASSET_REGISTRY_PATH;
+  // $FlowFixMe Metro configuration is immutable.
   config.resolver.hasteImplModulePath =
     config.resolver.hasteImplModulePath || defaultConfig.hasteImplModulePath;
+  // $FlowFixMe Metro configuration is immutable.
   config.resolver.platforms = config.resolver.platforms
     ? config.resolver.platforms.concat(defaultConfig.getPlatforms())
     : defaultConfig.getPlatforms();
+  // $FlowFixMe Metro configuration is immutable.
   config.resolver.providesModuleNodeModules = config.resolver
     .providesModuleNodeModules
     ? config.resolver.providesModuleNodeModules.concat(

local-cli/server/runServer.js

@@ -54,12 +54,19 @@ async function runServer(args: Args, config: ConfigT) {
 
   args.watchFolders.forEach(middlewareManager.serveStatic);
 
+  // $FlowFixMe Metro configuration is immutable.
   config.maxWorkers = args.maxWorkers;
+  // $FlowFixMe Metro configuration is immutable.
   config.server.port = args.port;
+  // $FlowFixMe Metro configuration is immutable.
   config.reporter = reporter;
+  // $FlowFixMe Metro configuration is immutable.
   config.resetCache = args.resetCache;
+  // $FlowFixMe Metro configuration is immutable.
   config.projectRoot = args.projectRoot;
+  // $FlowFixMe Metro configuration is immutable.
   config.watchFolders = args.watchFolders.slice(0);
+  // $FlowFixMe Metro configuration is immutable.
   config.server.enhanceMiddleware = middleware =>
     middlewareManager.getConnectInstance().use(middleware);