types(querycursor): correct cursor async iterator type with `populate…

…()` support

Fix #14374

test/types/querycursor.test.ts

@@ -20,3 +20,30 @@ Test.find().cursor().
     expectType<number>(i);
   }).
   then(() => console.log('Done!'));
+
+async function gh14374() {
+  // `Parent` represents the object as it is stored in MongoDB
+  interface Parent {
+    child?: Types.ObjectId
+    name?: string
+  }
+  const ParentModel = model<Parent>(
+    'Parent',
+    new Schema({
+        child: { type: Schema.Types.ObjectId, ref: 'Child' },
+        name: String
+    })
+  )
+
+  interface Child {
+    name: string
+  }
+  const childSchema: Schema = new Schema({ name: String });
+
+  // This does not
+  const cursor = ParentModel.find({}).populate<{ child: Child }>('child').cursor()
+  for await (const doc of cursor) {
+      const _t: string = doc.child.name;
+  }
+
+}

types/query.d.ts

@@ -208,7 +208,7 @@ declare module 'mongoose' {
      * A QueryCursor exposes a Streams3 interface, as well as a `.next()` function.
      * This is equivalent to calling `.cursor()` with no arguments.
      */
-    [Symbol.asyncIterator](): AsyncIterableIterator<DocType>;
+    [Symbol.asyncIterator](): AsyncIterableIterator<Unpacked<ResultType>>;
 
     /** Executes the query */
     exec(): Promise<ResultType>;
@@ -286,7 +286,7 @@ declare module 'mongoose' {
      * Returns a wrapper around a [mongodb driver cursor](https://mongodb.github.io/node-mongodb-native/4.9/classes/FindCursor.html).
      * A QueryCursor exposes a Streams3 interface, as well as a `.next()` function.
      */
-    cursor(options?: QueryOptions<DocType>): Cursor<DocType, QueryOptions<DocType>>;
+    cursor(options?: QueryOptions<DocType>): Cursor<Unpacked<ResultType>, QueryOptions<DocType>>;
 
     /**
      * Declare and/or execute this query as a `deleteMany()` operation. Works like