fix: allow calling Model.aggregate() with options

index.d.ts

@@ -731,8 +731,9 @@ declare module 'mongoose' {
   interface Model<T, TQueryHelpers = {}, TMethods = {}> extends NodeJS.EventEmitter, AcceptsDiscriminator {
     new(doc?: AnyKeys<T> & AnyObject): EnforceDocument<T, TMethods>;
 
-    aggregate<R = any>(pipeline?: any[]): Aggregate<Array<R>>;
+    aggregate<R = any>(pipeline?: any[], options?: Record<string, unknown>): Aggregate<Array<R>>;
     aggregate<R = any>(pipeline: any[], cb: Function): Promise<Array<R>>;
+    aggregate<R = any>(pipeline: any[], options: Record<string, unknown>, cb: Function): Promise<Array<R>>;
 
     /** Base Mongoose instance the model uses. */
     base: typeof mongoose;

lib/model.js

@@ -4135,15 +4135,16 @@ Model.mapReduce = function mapReduce(o, callback) {
  * @see Aggregate #aggregate_Aggregate
  * @see MongoDB http://docs.mongodb.org/manual/applications/aggregation/
  * @param {Array} [pipeline] aggregation pipeline as an array of objects
+ * @param {Object} [options] aggregation options
  * @param {Function} [callback]
  * @return {Aggregate}
  * @api public
  */
 
-Model.aggregate = function aggregate(pipeline, callback) {
+Model.aggregate = function aggregate(pipeline, options, callback) {
   _checkContext(this, 'aggregate');
 
-  if (arguments.length > 2 || get(pipeline, 'constructor.name') === 'Object') {
+  if (arguments.length > 3 || get(pipeline, 'constructor.name') === 'Object') {
     throw new MongooseError('Mongoose 5.x disallows passing a spread of operators ' +
       'to `Model.aggregate()`. Instead of ' +
       '`Model.aggregate({ $match }, { $skip })`, do ' +
@@ -4155,9 +4156,18 @@ Model.aggregate = function aggregate(pipeline, callback) {
     pipeline = [];
   }
 
+  if (typeof options === 'function') {
+    callback = options;
+    options = null;
+  }
+
   const aggregate = new Aggregate(pipeline || []);
   aggregate.model(this);
 
+  if (options != null) {
+    aggregate.option(options);
+  }
+
   if (typeof callback === 'undefined') {
     return aggregate;
   }