Use "babel-preset-react-native"

Rather than specifying Babel plugins in the `.babelrc` packaged with
react-native, leverage a Babel preset to define the plugins
(https://github.com/exponentjs/babel-preset-react-native).

This allows for a much better user experience for those who want (or
need) to override options in their project's `.babelrc`.

Prior to this PR, if a user wanted to use a custom babel-plugin (or a
custom set of babel plugins), they'd have either 1) manually override
the `.babelrc` in the react-packager directory (or fork RN), or 2)
specify a custom transformer to use when running the packager that
loaded their own `.babelrc`. Note - the custom transformer was
necessary because without it, RN's `.babelrc` options would supersede
the options defined in the project's `.babelrc`...potentially causing
issues with plugin ordering.

This PR makes the transformer check for the existence of a
project-level `.babelrc`, and if it it's there, it _doesn't_ use the
react-native `.babelrc`. This prevents any oddities with Babel plugin
ordering, and leaves that up to the RN user. The RN user would then
just include a `.babelrc` file in their project that looks like:

```
{
"presets": ["react-native"]
}
```

They can then add whatever other presets or plugins that they'd like
(such as the Babel Relay Plugin or a decorators plugin, for example).

package.json

@@ -108,35 +108,12 @@
   "dependencies": {
     "absolute-path": "^0.0.0",
     "art": "^0.10.0",
-    "babel-core": "^6.1.20",
-    "babel-plugin-external-helpers-2": "^6.1.4",
-    "babel-plugin-syntax-async-functions": "^6.0.14",
-    "babel-plugin-syntax-class-properties": "^6.0.14",
-    "babel-plugin-syntax-flow": "^6.0.14",
-    "babel-plugin-syntax-jsx": "^6.0.14",
-    "babel-plugin-syntax-trailing-function-commas": "^6.0.14",
-    "babel-plugin-transform-class-properties": "^6.0.14",
-    "babel-plugin-transform-es2015-arrow-functions": "^6.0.14",
-    "babel-plugin-transform-es2015-block-scoping": "^6.0.18",
-    "babel-plugin-transform-es2015-classes": "^6.1.2",
-    "babel-plugin-transform-es2015-computed-properties": "^6.0.14",
-    "babel-plugin-transform-es2015-constants": "^6.0.15",
-    "babel-plugin-transform-es2015-destructuring": "^6.0.18",
-    "babel-plugin-transform-es2015-for-of": "^6.0.14",
-    "babel-plugin-transform-es2015-modules-commonjs": "^6.1.3",
-    "babel-plugin-transform-es2015-parameters": "^6.0.18",
-    "babel-plugin-transform-es2015-shorthand-properties": "^6.0.14",
-    "babel-plugin-transform-es2015-spread": "^6.0.14",
-    "babel-plugin-transform-es2015-template-literals": "^6.0.14",
-    "babel-plugin-transform-flow-strip-types": "^6.0.14",
-    "babel-plugin-transform-object-assign": "^6.0.14",
-    "babel-plugin-transform-object-rest-spread": "^6.0.14",
-    "babel-plugin-transform-react-display-name": "^6.0.14",
-    "babel-plugin-transform-react-jsx": "^6.0.18",
-    "babel-plugin-transform-regenerator": "^6.0.18",
-    "babel-polyfill": "^6.0.16",
-    "babel-types": "^6.1.2",
-    "babylon": "^6.1.2",
+    "babel-core": "~6.4.0",
+    "babel-plugin-external-helpers": "~6.4.0",
+    "babel-preset-react-native": "^1.0.0",
+    "babel-polyfill": "~6.3.14",
+    "babel-types": "~6.4.1",
+    "babylon": "~6.4.2",
     "base64-js": "^0.0.8",
     "bser": "^1.0.2",
     "chalk": "^1.1.1",

packager/babelRegisterOnly.js

@@ -16,7 +16,7 @@ var path = require('path');
 var _only = [];
 
 function readBabelRC() {
-  var rcpath = path.join(__dirname, 'react-packager', '.babelrc');
+  var rcpath = path.join(__dirname, 'react-packager', '.babelrc.json');
   var source = fs.readFileSync(rcpath).toString();
   return JSON.parse(source);
 }

packager/react-packager/.babelrc.json

@@ -0,0 +1,4 @@
+{
+  "presets": [ "react-native" ],
+  "plugins": []
+}

packager/transformer.js

@@ -16,30 +16,49 @@ const inlineRequires = require('fbjs-scripts/babel-6/inline-requires');
 const json5 = require('json5');
 const path = require('path');
 const ReactPackager = require('./react-packager');
-const resolvePlugins = require('./react-packager/src/JSTransformer/resolvePlugins');
 
-const babelRC =
-  json5.parse(
-    fs.readFileSync(
-      path.resolve(__dirname, 'react-packager', '.babelrc')));
 
-function transform(src, filename, options) {
-  options = options || {};
+const projectBabelRCPath = path.resolve(__dirname, '..', '..', '..', '.babelrc');
+
+let babelRC = { plugins: [] };
 
-  const extraPlugins = ['external-helpers-2'];
+// If a babelrc exists in the project,
+// don't use the one provided with react-native.
+if (!fs.existsSync(projectBabelRCPath)) {
+  babelRC = json5.parse(
+    fs.readFileSync(
+      path.resolve(__dirname, 'react-packager', '.babelrc.json')));
+}
+
+/**
+ * Given a filename and options, build a Babel
+ * config object with the appropriate plugins.
+ */
+function buildBabelConfig(filename, options) {
   const extraConfig = {
     filename,
     sourceFileName: filename,
   };
 
   const config = Object.assign({}, babelRC, extraConfig);
 
+  // Add extra plugins
+  const extraPlugins = [require('babel-plugin-external-helpers')];
+
   if (options.inlineRequires) {
     extraPlugins.push(inlineRequires);
   }
-  config.plugins = resolvePlugins(extraPlugins.concat(config.plugins));
 
-  const result = babel.transform(src, Object.assign({}, babelRC, config));
+  config.plugins = extraPlugins.concat(config.plugins);
+
+  return Object.assign({}, babelRC, extraConfig);
+}
+
+function transform(src, filename, options) {
+  options = options || {};
+
+  const babelConfig = buildBabelConfig(filename, options);
+  const result = babel.transform(src, babelConfig);
 
   return {
     code: result.code,