Add readCurrentRevision helper

Summary: To read the current revision written into the manifest at build-time.

Reviewed By: danielbuechele

Differential Revision: D14454983

fbshipit-source-id: adad7d85dbf410701d2f8601bfccbcfbc0f30dff

src/utils/__tests__/packageMetadata.node.js

@@ -0,0 +1,13 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+import {readCurrentRevision} from '../packageMetadata.js';
+
+test('readCurrentRevision does not return something meaningful in dev mode', async () => {
+  const ret = await readCurrentRevision();
+  expect(ret).toBeUndefined();
+});

src/utils/packageMetadata.js

@@ -0,0 +1,29 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+import electron from 'electron';
+import lodash from 'lodash';
+import isProduction from './isProduction';
+import path from 'path';
+import fs from 'fs';
+import {promisify} from 'util';
+
+const getPackageJSON = async () => {
+  const base =
+    isProduction() && electron.remote
+      ? electron.remote.app.getAppPath()
+      : process.cwd();
+  const content = await promisify(fs.readFile)(path.join(base, 'package.json'));
+  return JSON.parse(content);
+};
+
+export const readCurrentRevision: () => Promise<?string> = lodash.memoize(
+  async () => {
+    const json = await getPackageJSON();
+    return json.revision;
+  },
+);