feat(NODE-4519): deprecate promiseLibrary and PromiseProvider

src/mongo_client.ts

@@ -230,7 +230,10 @@ export interface MongoClientOptions extends BSONSerializeOptions, SupportedNodeC
   raw?: boolean;
   /** A primary key factory function for generation of custom `_id` keys */
   pkFactory?: PkFactory;
-  /** A Promise library class the application wishes to use such as Bluebird, must be ES6 compatible */
+  /**
+   * A Promise library class the application wishes to use such as Bluebird, must be ES6 compatible
+   * @deprecated Setting a custom promise library is deprecated the next major version will use the global Promise constructor only.
+   */
   promiseLibrary?: any;
   /** The logging level */
   loggerLevel?: LoggerLevel;

test/integration/node-specific/custom_promise_library.test.js

@@ -1,7 +1,9 @@
 'use strict';
 
+const { once } = require('events');
 const { expect } = require('chai');
 const { PromiseProvider } = require('../../../src/promise_provider');
+const { MongoClient } = require('../../../src/mongo_client');
 
 class CustomPromise extends Promise {}
 CustomPromise.prototype.isCustomMongo = true;
@@ -11,6 +13,13 @@ describe('Optional PromiseLibrary', function () {
     PromiseProvider.set(Promise);
   });
 
+  it('should emit a deprecation warning when a promiseLibrary is set', async () => {
+    const willEmitWarning = once(process, 'warning');
+    new MongoClient('mongodb://iLoveJavascript', { promiseLibrary: () => {} });
+    const [warning] = await willEmitWarning;
+    expect(warning).to.have.property('message', 'promiseLibrary is a deprecated option');
+  });
+
   it('should correctly implement custom dependency-less promise', function (done) {
     const getCustomPromise = v => new CustomPromise(resolve => resolve(v));
     const getNativePromise = v => new Promise(resolve => resolve(v));

test/types/mongodb.test-d.ts

@@ -27,6 +27,7 @@ declare const options: MongoDBDriver.MongoClientOptions;
 expectDeprecated(options.w);
 expectDeprecated(options.journal);
 expectDeprecated(options.wtimeoutMS);
+expectDeprecated(options.promiseLibrary);
 expectNotDeprecated(options.writeConcern);
 expectType<WriteConcernSettings | WriteConcern | undefined>(options.writeConcern);