[react-packager] Fix more node_modules resolution rules

Summary:
@public
Fixes #773
This fixes `.json` name resolution. And also reads `package.json` when doing a directory module resolution.
The algorithm can be found here: https://nodejs.org/api/modules.html
I'll probably start including the node (or browserify) modules test in later diffs to make sure we're fully compliant.

Test Plan:
* ./runJestTests.sh
* ./runJestTests.sh PackagerIntegration
* open playground and require a json file
* test redbox

packager/react-packager/src/DependencyResolver/haste/DependencyGraph/__tests__/DependencyGraph-test.js

@@ -168,9 +168,11 @@ describe('DependencyGraph', function() {
             '/**',
             ' * @providesModule index',
             ' */',
-            'require("./a.json")'
+            'require("./a.json")',
+            'require("./b")'
           ].join('\n'),
           'a.json': JSON.stringify({}),
+          'b.json': JSON.stringify({}),
         }
       });
 
@@ -186,7 +188,7 @@ describe('DependencyGraph', function() {
               id: 'index',
               altId: 'package/index',
               path: '/root/index.js',
-              dependencies: ['./a.json'],
+              dependencies: ['./a.json', './b'],
               isAsset: false,
               isAsset_DEPRECATED: false,
               isJSON: undefined,
@@ -205,6 +207,17 @@ describe('DependencyGraph', function() {
               resolution: undefined,
               resolveDependency: undefined,
             },
+            {
+              id: 'package/b.json',
+              isJSON: true,
+              path: '/root/b.json',
+              dependencies: [],
+              isAsset: false,
+              isAsset_DEPRECATED: false,
+              isPolyfill: false,
+              resolution: undefined,
+              resolveDependency: undefined,
+            },
           ]);
       });
     });
@@ -851,6 +864,58 @@ describe('DependencyGraph', function() {
       });
     });
 
+    pit('should resolve require to main if it is a dir w/ a package.json', function() {
+      var root = '/root';
+      fs.__setMockFilesystem({
+        'root': {
+          'package.json': JSON.stringify({
+            name: 'test',
+          }),
+          'index.js': 'require("./lib/")',
+          lib: {
+            'package.json': JSON.stringify({
+              'main': 'main.js',
+            }),
+            'index.js': 'lol',
+            'main.js': 'lol',
+          },
+        }
+      });
+
+      var dgraph = new DependencyGraph({
+        roots: [root],
+        fileWatcher: fileWatcher,
+        assetExts: ['png', 'jpg'],
+      });
+      return dgraph.getOrderedDependencies('/root/index.js').then(function(deps) {
+        expect(getDataFromModules(deps))
+          .toEqual([
+            {
+              id: 'test/index',
+              path: '/root/index.js',
+              dependencies: ['./lib/'],
+              isAsset: false,
+              isAsset_DEPRECATED: false,
+              isJSON: undefined,
+              isPolyfill: false,
+              resolution: undefined,
+              resolveDependency: undefined,
+            },
+            {
+              id: '/root/lib/main.js',
+              path: '/root/lib/main.js',
+              dependencies: [],
+              isAsset: false,
+              isAsset_DEPRECATED: false,
+              isJSON: undefined,
+              isPolyfill: false,
+              resolution: undefined,
+              resolveDependency: undefined,
+            },
+          ]);
+      });
+    });
+
     pit('should ignore malformed packages', function() {
       var root = '/root';
       fs.__setMockFilesystem({

packager/react-packager/src/DependencyResolver/haste/DependencyGraph/index.js

@@ -1,6 +1,3 @@
-// TODO
-// Fix it to work with tests
-
 /**
  * Copyright (c) 2015-present, Facebook, Inc.
  * All rights reserved.
@@ -296,16 +293,18 @@ DependecyGraph.prototype.resolveDependency = function(
     modulePath = path.join(dir, depModuleId);
     modulePath = browserFieldRedirect(packageJson, modulePath);
 
-    // JS modules can be required without extensios.
-    if (!this._isFileAsset(modulePath) && !modulePath.match(/\.json$/)) {
-      modulePath = withExtJs(modulePath);
-    }
+    dep = this._graph[modulePath] ||
+      this._graph[modulePath + '.js'] ||
+      this._graph[modulePath + '.json'];
 
-    dep = this._graph[modulePath];
-
-    // Maybe the dependency is a directory and there is an index.js inside it.
+    // Maybe the dependency is a directory and there is a packageJson and/or index.js inside it.
     if (dep == null) {
-      dep = this._graph[path.join(dir, depModuleId, 'index.js')];
+      var dirPackageJson = this._packageByRoot[path.join(dir, depModuleId).replace(/\/$/, '')];
+      if (dirPackageJson) {
+        dep = this._resolvePackageMain(dirPackageJson);
+      } else {
+        dep = this._graph[path.join(dir, depModuleId, 'index.js')];
+      }
     }
 
     // Maybe it's an asset with @n.nx resolution and the path doesn't map
@@ -444,14 +443,6 @@ DependecyGraph.prototype._processPackage = function(packagePath) {
         return Promise.resolve();
       }
 
-      if (packageJson.name == null) {
-        debug(
-          'WARNING: package.json `%s` is missing a name field',
-          packagePath
-        );
-        return Promise.resolve();
-      }
-
       packageJson._root = packageRoot;
       self._addPackageToIndices(packageJson);
 
@@ -461,14 +452,14 @@ DependecyGraph.prototype._processPackage = function(packagePath) {
 
 DependecyGraph.prototype._addPackageToIndices = function(packageJson) {
   this._packageByRoot[packageJson._root] = packageJson;
-  if (!this._isInNodeModules(packageJson._root)) {
+  if (!this._isInNodeModules(packageJson._root) && packageJson.name != null) {
     this._packagesById[packageJson.name] = packageJson;
   }
 };
 
 DependecyGraph.prototype._removePackageFromIndices = function(packageJson) {
   delete this._packageByRoot[packageJson._root];
-  if (!this._isInNodeModules(packageJson._root)) {
+  if (!this._isInNodeModules(packageJson._root) && packageJson.name != null) {
     delete this._packagesById[packageJson.name];
   }
 };
@@ -536,7 +527,7 @@ DependecyGraph.prototype._processModule = function(modulePath) {
  */
 DependecyGraph.prototype._lookupName = function(modulePath) {
   var packageJson = this._lookupPackage(modulePath);
-  if (packageJson == null) {
+  if (packageJson == null || packageJson.name == null) {
     return path.resolve(modulePath);
   } else {
     var relativePath =