test: add some docs

test/types/queries.test.ts

@@ -678,3 +678,12 @@
     $expr: { $lt: [{ $size: '$owners' }, 10] }
   };
 }
+
+function gh14510() {
+  // From https://stackoverflow.com/questions/56505560/how-to-fix-ts2322-could-be-instantiated-with-a-different-subtype-of-constraint:
+  // "Never assign a concrete type to a generic type parameter, consider it as read-only!"
+  // This function is generally something you shouldn't do in TypeScript, can work around it with `as` though.
+  function findById<ModelType extends {_id: Types.ObjectId | string}>(model: Model<ModelType>, _id: Types.ObjectId | string) {
+    return model.find({_id: _id} as FilterQuery<ModelType>);
+  }
+}

types/query.d.ts

@@ -26,7 +26,7 @@ declare module 'mongoose' {
    * { age: { $gte: 30 } }
    * ```
    */
-  type RootFilterQuery<T> = FilterQuery<T> | Query<any, any> | Types.ObjectId;
+  type RootFilterQuery<T> = FilterQuery<T>;
 
   type FilterQuery<T> = { [P in keyof T]?: Condition<T[P]>; } & RootQuerySelector<T>;