Handle JSON modules encoded with a BOM (jestjs#2564)

* Handle JSON modules encoded with a BOM

* fixup! Handle JSON modules encoded with a BOM

packages/jest-runtime/package.json

@@ -22,6 +22,7 @@
     "jest-util": "^18.1.0",
     "json-stable-stringify": "^1.0.0",
     "micromatch": "^2.3.11",
+    "strip-bom": "3.0.0",
     "yargs": "^6.3.0"
   },
   "bin": {

packages/jest-runtime/src/__tests__/Runtime-requireModule-test.js

@@ -274,4 +274,24 @@ describe('Runtime requireModule', () => {
     ]),
   );
 
+  it('finds modules encoded in UTF-8 *with BOM*', () =>
+    createRuntime(__filename).then(runtime => {
+      const exports = runtime.requireModule(
+        runtime.__mockRootPath,
+        './UTF8WithBOM.js',
+      );
+      expect(exports).toBe('isModuleEncodedInUTF8WithBOM');
+    }),
+  );
+
+  it('finds and loads JSON files encoded in UTF-8 *with BOM*', () =>
+    createRuntime(__filename).then(runtime => {
+      const exports = runtime.requireModule(
+        runtime.__mockRootPath,
+        './UTF8WithBOM.json',
+      );
+      expect(exports.isJSONModuleEncodedInUTF8WithBOM).toBe(true);
+    }),
+  );
+
 });

packages/jest-runtime/src/__tests__/test_root/UTF8WithBOM.js

@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+'use strict';
+
+module.exports = 'isModuleEncodedInUTF8WithBOM';

packages/jest-runtime/src/__tests__/test_root/UTF8WithBOM.json

@@ -0,0 +1 @@
+{"isJSONModuleEncodedInUTF8WithBOM": true}

packages/jest-runtime/src/index.js

@@ -22,6 +22,7 @@ const Resolver = require('jest-resolve');
 
 const fs = require('graceful-fs');
 const path = require('path');
+const stripBOM = require('strip-bom');
 const shouldInstrument = require('./shouldInstrument');
 const transform = require('./transform');
 const {
@@ -290,7 +291,7 @@ class Runtime {
       moduleRegistry[modulePath] = localModule;
       if (path.extname(modulePath) === '.json') {
         localModule.exports = this._environment.global.JSON.parse(
-          fs.readFileSync(modulePath, 'utf8'),
+          stripBOM(fs.readFileSync(modulePath, 'utf8'))
         );
       } else if (path.extname(modulePath) === '.node') {
         // $FlowFixMe