feat(NODE-4521)!: remove custom promise library support

Author: nbbeeken

etc/notes/CHANGES_5.0.0.md

@@ -28,3 +28,8 @@ npm install --save snappy@7
 ### Minimum supported Node version
 
 The new minimum supported Node.js version is now 14.20.1.
+
+### Custom Promise library support removed
+
+The MongoClient option `promiseLibrary` along with the `Promise.set` export that allows specifying a custom promise library has been removed.
+This allows the driver to adopt async/await syntax which has [performance benefits](https://v8.dev/blog/fast-async) over manual promise construction.

package-lock.json

@@ -60,7 +60,6 @@
     "@types/whatwg-url": "^11.0.0",
     "@typescript-eslint/eslint-plugin": "^5.40.0",
     "@typescript-eslint/parser": "^5.40.0",
-    "bluebird": "^3.7.2",
     "chai": "^4.3.6",
     "chai-subset": "^1.6.0",
     "chalk": "^4.1.2",

package.json

@@ -25,7 +25,6 @@ import {
   ServerApiVersion
 } from './mongo_client';
 import { MongoLogger, MongoLoggerEnvOptions, MongoLoggerMongoClientOptions } from './mongo_logger';
-import { PromiseProvider } from './promise_provider';
 import { ReadConcern, ReadConcernLevel } from './read_concern';
 import { ReadPreference, ReadPreferenceMode } from './read_preference';
 import type { TagSet } from './sdam/server_description';
@@ -431,10 +430,6 @@ export function parseOptions(
     mongoOptions.dbName = 'test';
   }
 
-  if (options.promiseLibrary) {
-    PromiseProvider.set(options.promiseLibrary);
-  }
-
   validateLoadBalancedOptions(hosts, mongoOptions, isSRV);
 
   if (mongoClient && mongoOptions.autoEncryption) {
@@ -960,10 +955,6 @@ export const OPTIONS = {
       );
     }
   },
-  promiseLibrary: {
-    deprecated: true,
-    type: 'any'
-  },
   promoteBuffers: {
     type: 'boolean'
   },

src/connection_string.ts

@@ -17,7 +17,6 @@ import { TODO_NODE_3286, TypedEventEmitter } from '../mongo_types';
 import { executeOperation, ExecutionResult } from '../operations/execute_operation';
 import { GetMoreOperation } from '../operations/get_more';
 import { KillCursorsOperation } from '../operations/kill_cursors';
-import { PromiseProvider } from '../promise_provider';
 import { ReadConcern, ReadConcernLike } from '../read_concern';
 import { ReadPreference, ReadPreferenceLike } from '../read_preference';
 import type { Server } from '../sdam/server';
@@ -297,47 +296,36 @@ export abstract class AbstractCursor<
     return bufferedDocs;
   }
 
-  [Symbol.asyncIterator](): AsyncIterator<TSchema, void> {
-    async function* nativeAsyncIterator(this: AbstractCursor<TSchema>) {
-      if (this.closed) {
-        return;
-      }
+  async *[Symbol.asyncIterator](): AsyncIterator<TSchema, void> {
+    if (this.closed) {
+      return;
+    }
 
-      while (true) {
-        const document = await this.next();
+    while (true) {
+      const document = await this.next();
 
-        // Intentional strict null check, because users can map cursors to falsey values.
-        // We allow mapping to all values except for null.
-        // eslint-disable-next-line no-restricted-syntax
-        if (document === null) {
-          if (!this.closed) {
-            const message =
-              'Cursor returned a `null` document, but the cursor is not exhausted.  Mapping documents to `null` is not supported in the cursor transform.';
+      // Intentional strict null check, because users can map cursors to falsey values.
+      // We allow mapping to all values except for null.
+      // eslint-disable-next-line no-restricted-syntax
+      if (document === null) {
+        if (!this.closed) {
+          const message =
+            'Cursor returned a `null` document, but the cursor is not exhausted.  Mapping documents to `null` is not supported in the cursor transform.';
 
-            await cleanupCursorAsync(this, { needsToEmitClosed: true }).catch(() => null);
+          await cleanupCursorAsync(this, { needsToEmitClosed: true }).catch(() => null);
 
-            throw new MongoAPIError(message);
-          }
-          break;
-        }
-
-        yield document;
-
-        if (this[kId] === Long.ZERO) {
-          // Cursor exhausted
-          break;
+          throw new MongoAPIError(message);
         }
+        break;
       }
-    }
 
-    const iterator = nativeAsyncIterator.call(this);
+      yield document;
 
-    if (PromiseProvider.get() == null) {
-      return iterator;
+      if (this[kId] === Long.ZERO) {
+        // Cursor exhausted
+        break;
+      }
     }
-    return {
-      next: () => maybeCallback(() => iterator.next(), null)
-    };
   }
 
   stream(options?: CursorStreamOptions): Readable & AsyncIterable<TSchema> {

src/cursor/abstract_cursor.ts

@@ -16,7 +16,6 @@ import { GridFSBucketWriteStream } from './gridfs/upload';
 import { Logger } from './logger';
 import { MongoClient } from './mongo_client';
 import { CancellationToken } from './mongo_types';
-import { PromiseProvider } from './promise_provider';
 import { ClientSession } from './sessions';
 
 /** @internal */
@@ -100,9 +99,6 @@ export {
   UnorderedBulkOperation
 };
 
-// Deprecated, remove in next major
-export { PromiseProvider as Promise };
-
 // enums
 export { BatchType } from './bulk/common';
 export { GSSAPICanonicalizationValue } from './cmap/auth/gssapi';

src/index.ts

@@ -228,11 +228,6 @@ export interface MongoClientOptions extends BSONSerializeOptions, SupportedNodeC
   forceServerObjectId?: 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
-   * @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?: LegacyLoggerLevel;
   /** Custom logger object */
@@ -743,7 +738,6 @@ export interface MongoOptions
         | 'monitorCommands'
         | 'noDelay'
         | 'pkFactory'
-        | 'promiseLibrary'
         | 'raw'
         | 'replicaSet'
         | 'retryReads'

src/mongo_client.ts

@@ -25,7 +25,6 @@ import type { MongoClient, MongoOptions } from './mongo_client';
 import { TypedEventEmitter } from './mongo_types';
 import { executeOperation } from './operations/execute_operation';
 import { RunAdminCommandOperation } from './operations/run_command';
-import { PromiseProvider } from './promise_provider';
 import { ReadConcernLevel } from './read_concern';
 import { ReadPreference } from './read_preference';
 import { _advanceClusterTime, ClusterTime, TopologyType } from './sdam/common';
@@ -605,8 +604,7 @@ function attemptTransaction<TSchema>(
   try {
     promise = fn(session);
   } catch (err) {
-    const PromiseConstructor = PromiseProvider.get() ?? Promise;
-    promise = PromiseConstructor.reject(err);
+    promise = Promise.reject(err);
   }
 
   if (!isPromiseLike(promise)) {

src/promise_provider.ts

@@ -23,7 +23,6 @@ import type { Explain } from './explain';
 import type { MongoClient } from './mongo_client';
 import type { CommandOperationOptions, OperationParent } from './operations/command';
 import type { Hint, OperationOptions } from './operations/operation';
-import { PromiseProvider } from './promise_provider';
 import { ReadConcern } from './read_concern';
 import { ReadPreference } from './read_preference';
 import { ServerType } from './sdam/common';
@@ -445,17 +444,9 @@ export function maybeCallback<T>(
   promiseFn: () => Promise<T>,
   callback?: Callback<T> | null
 ): Promise<T> | void {
-  const PromiseConstructor = PromiseProvider.get();
-
   const promise = promiseFn();
   if (callback == null) {
-    if (PromiseConstructor == null) {
-      return promise;
-    } else {
-      return new PromiseConstructor((resolve, reject) => {
-        promise.then(resolve, reject);
-      });
-    }
+    return promise;
   }
 
   promise.then(