Resolve path at callsite rather than in `Config.loadFile`

Summary:
Resolve path at callsite rather than in `Config.loadFile`

`Config.loadFile` should not expose unexpected behavior as joining paths together. This moves that responsibility to the call site. `path.resolve` returns the second argument if it is an absolute path.

Reviewed By: bestander

Differential Revision: D4986130

fbshipit-source-id: c80a588ffa86011bcd5a2c393ad5d6eedc6c61ae

local-cli/core/index.js

@@ -14,6 +14,7 @@ const Config = require('../util/Config');
 
 const defaultConfig = require('./default.config');
 const minimist = require('minimist');
+const path = require('path');
 
 import type {CommandT} from '../commands';
 import type {ConfigT} from '../util/Config';
@@ -40,7 +41,7 @@ export type RNConfig = {
 function getCliConfig(): RNConfig {
   const cliArgs = minimist(process.argv.slice(2));
   const config = cliArgs.config != null
-    ? Config.loadFile(cliArgs.config, __dirname)
+    ? Config.loadFile(path.resolve(__dirname, cliArgs.config))
     : Config.findOptional(__dirname);
 
   return {...defaultConfig, ...config};

local-cli/util/Config.js

@@ -122,15 +122,9 @@ const Config = {
       : {...defaultConfig};
   },
 
-  loadFile(
-    pathToConfig: string,
-    cwd: string,
-  ): ConfigT {
-    const config: {} = path.isAbsolute(pathToConfig) ?
-      // $FlowFixMe nope
-      require(pathToConfig) :
-      // $FlowFixMe nope
-      require(path.join(cwd, pathToConfig));
+  loadFile(pathToConfig: string): ConfigT {
+    //$FlowFixMe: necessary dynamic require
+    const config: {} = require(pathToConfig);
     return {...defaultConfig, ...config};
   },
 };