Define global logger instance to be used for all logging

Summary:
The advantage of this is that anyone can now log without needing to carry around a Logger object.
Primary reason is for making metrics less intrusive in the codebase.

Reviewed By: passy

Differential Revision: D13671368

fbshipit-source-id: 162ab1351a124683aef13983fc3bcec01385cd1a

src/utils/__tests__/metrics.node.js

@@ -1,58 +0,0 @@
-/**
- * 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 {recordSuccessMetric} from '../metrics';
-import type Logger from '../../fb-stubs/Logger';
-
-//$FlowFixMe pretend logger is the right type
-const logger: Logger = {
-  track: jest.fn(),
-};
-
-beforeAll(() => {
-  logger.track.mockClear();
-});
-
-test('Wrapping a successful promise preserves result and logs correctly', () => {
-  const successPromise = Promise.resolve('Yay!');
-  const wrappedPromise = recordSuccessMetric(
-    successPromise,
-    'test metric',
-    logger,
-  );
-  return wrappedPromise
-    .then(wrappedValue => {
-      expect(wrappedValue).toBe('Yay!');
-    })
-    .then(() => {
-      expect(logger.track).toHaveBeenCalledWith(
-        'success-rate',
-        'test metric',
-        1,
-      );
-    });
-});
-
-test('Wrapping a rejected promise preserves result and logs correctly', () => {
-  const successPromise = Promise.reject('Oh no!');
-  const wrappedPromise = recordSuccessMetric(
-    successPromise,
-    'test metric',
-    logger,
-  );
-  expect.assertions(2); // Make sure to fail if catch block isn't visited
-  return wrappedPromise
-    .catch(wrappedValue => {
-      expect(wrappedValue).toBe('Oh no!');
-    })
-    .then(() => {
-      expect(logger.track).toHaveBeenCalledWith(
-        'success-rate',
-        'test metric',
-        0,
-      );
-    });
-});

src/utils/metrics.js

@@ -5,7 +5,7 @@
  * @format
  */
 
-import type Logger from '../fb-stubs/Logger';
+import {getInstance} from '../fb-stubs/Logger';
 
 /*
  * Wraps a Promise, preserving it's functionality but logging the success or
@@ -15,15 +15,14 @@ import type Logger from '../fb-stubs/Logger';
 export function recordSuccessMetric(
   promise: Promise<*>,
   name: string,
-  logger: Logger,
 ): Promise<*> {
   return promise.then(
     fulfilledValue => {
-      logger.track('success-rate', name, 1);
+      getInstance().track('success-rate', name, 1);
       return fulfilledValue;
     },
     rejectionReason => {
-      logger.track('success-rate', name, 0);
+      getInstance().track('success-rate', name, 0);
       return Promise.reject(rejectionReason);
     },
   );