Add `--config` option to CLI to allow passing a path to an `rn-cli.config.js`

Summary:
Currently we just try to resolve a rn-cli.config.js file by walking up the tree from node_modules/react-native. In non-standard uses of RN, when your copy of RN may not live within node_modules, it's impossible to use rn-cli.config.js. This PR adds a "config" flag to the cli that let's you pass in a path to rn-cli.config.js.

cc ide
Closes https://github.com/facebook/react-native/pull/7883

Differential Revision: D3382823

Pulled By: bestander

fbshipit-source-id: b946f3bb355050fc2fe99273d0e99e441dbed111

local-cli/cliEntry.js

@@ -16,6 +16,7 @@ const Config = require('./util/Config');
 const childProcess = require('child_process');
 const Promise = require('promise');
 const chalk = require('chalk');
+const minimist = require('minimist');
 const path = require('path');
 const fs = require('fs');
 const gracefulFs = require('graceful-fs');
@@ -121,16 +122,38 @@ const addCommand = (command: Command, config: Config) => {
       opt.parse || defaultOptParser,
       typeof opt.default === 'function' ? opt.default(config) : opt.default,
     ));
+
+  // Placeholder option for --config, which is parsed before any other option,
+  // but needs to be here to avoid "unknown option" errors when specified
+  cmd.option('--config [string]', 'Path to the CLI configuration file');
 };
 
+function getCliConfig() {
+  // Use a lightweight option parser to look up the CLI configuration file,
+  // which we need to set up the parser for the other args and options
+  let cliArgs = minimist(process.argv.slice(2));
+
+  let cwd;
+  let configPath;
+  if (cliArgs.config != null) {
+    cwd = process.cwd();
+    configPath = cliArgs.config;
+  } else {
+    cwd = __dirname;
+    configPath = Config.findConfigPath(cwd);
+  }
+
+  return Config.get(cwd, defaultConfig, configPath);
+}
+
 function run() {
-  const config = Config.get(__dirname, defaultConfig);
   const setupEnvScript = /^win/.test(process.platform)
     ? 'setup_env.bat'
     : 'setup_env.sh';
 
   childProcess.execFileSync(path.join(__dirname, setupEnvScript));
 
+  const config = getCliConfig();
   commands.forEach(cmd => addCommand(cmd, config));
 
   commander.parse(process.argv);

local-cli/util/Config.js

@@ -8,11 +8,11 @@
  */
 'use strict';
 
+const assert = require('assert');
 const fs = require('fs');
 const path = require('path');
 
 const RN_CLI_CONFIG = 'rn-cli.config.js';
-let cachedConfig = null;
 
 /**
  * Module capable of getting the configuration that should be used for
@@ -25,26 +25,37 @@ let cachedConfig = null;
  * error will be thrown.
  */
 const Config = {
-  get(cwd, defaultConfig) {
-    if (cachedConfig) {
-      return cachedConfig;
+  get(cwd, defaultConfig, pathToConfig) {
+    let baseConfig;
+
+    // Handle the legacy code path where pathToConfig is unspecified
+    if (pathToConfig === undefined) {
+      const configPath = Config.findConfigPath(cwd);
+      if (!configPath && !defaultConfig) {
+        throw new Error(
+          `Can't find "${RN_CLI_CONFIG}" file in any parent folder of "${cwd}"`
+        );
+      }
+      baseConfig = require(configPath);
+    } else if (pathToConfig == null) {
+      assert(defaultConfig, 'Must have a default config if config is missing');
+    } else {
+      baseConfig = path.isAbsolute(pathToConfig) ?
+        require(pathToConfig) :
+        require(path.join(cwd, pathToConfig));
     }
 
+    return {
+      ...defaultConfig,
+      ...baseConfig,
+      cwd,
+    };
+  },
+
+  findConfigPath(cwd) {
     const parentDir = findParentDirectory(cwd, RN_CLI_CONFIG);
-    if (!parentDir && !defaultConfig) {
-      throw new Error(
-        `Can't find "rn-cli.config.js" file in any parent folder of "${cwd}"`
-      );
-    }
-
-    const config = parentDir
-      ? require(path.join(parentDir, RN_CLI_CONFIG))
-      : {};
-
-    cachedConfig = Object.assign({}, defaultConfig, config);
-    cachedConfig.cwd = cwd;
-    return cachedConfig;
-  }
+    return parentDir ? path.join(parentDir, RN_CLI_CONFIG) : null;
+  },
 };
 
 // Finds the most near ancestor starting at `currentFullPath` that has

package.json

@@ -148,6 +148,7 @@
     "connect": "^2.8.3",
     "core-js": "^2.2.2",
     "debug": "^2.2.0",
+    "denodeify": "^1.2.1",
     "event-target-shim": "^1.0.5",
     "fbjs": "^0.8.3",
     "fbjs-scripts": "^0.7.0",
@@ -163,6 +164,8 @@
     "jstransform": "^11.0.3",
     "lodash": "^3.10.1",
     "mime": "^1.3.4",
+    "mime-types": "2.1.11",
+    "minimist": "^1.2.0",
     "mkdirp": "^0.5.1",
     "module-deps": "^3.9.1",
     "node-fetch": "^1.3.3",
@@ -183,6 +186,7 @@
     "stacktrace-parser": "^0.1.3",
     "temp": "0.8.3",
     "uglify-js": "^2.6.2",
+    "whatwg-fetch": "^1.0.0",
     "wordwrap": "^1.0.0",
     "worker-farm": "^1.3.1",
     "ws": "^1.1.0",
@@ -190,10 +194,7 @@
     "xmldoc": "^0.4.0",
     "yargs": "^3.24.0",
     "yeoman-environment": "1.5.3",
-    "yeoman-generator": "0.21.2",
-    "mime-types": "2.1.11",
-    "whatwg-fetch": "^1.0.0",
-    "denodeify": "^1.2.1"
+    "yeoman-generator": "0.21.2"
   },
   "devDependencies": {
     "babel-eslint": "^6.0.0",