Return type of document.depopulate() is still the populated document type

[blowfishlol]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.6.1

Node.js version

18.19.0

MongoDB server version

6.0.15 Community

Typescript version (if applicable)

5.6.2

Description

When populating a document, and then depopulating it, the type will remain as if the document is still populated.

When testing in 8.3.1, the return type from a depopulate() method is the original document type.

Steps to Reproduce

import { type Types, Schema, connect, model } from 'mongoose';
type CarObjectInterface = {
  make: string;
  model: string;
  year: number;
  owner: Types.ObjectId;
};
const carSchema = new Schema<CarObjectInterface>({
  make: { type: String, required: true },
  model: { type: String, required: true },
  year: { type: Number, required: true },
  owner: { type: Schema.Types.ObjectId, ref: 'User' }
});

type UserObjectInterface = {
  name: string;
  age: number;
};
const userSchema = new Schema<UserObjectInterface>({
  name: String,
  age: Number
});

async function main() {
  await connect('mongodb://localhost:27017/playground');
  const Car = model<CarObjectInterface>('Car', carSchema);
  const User = model<UserObjectInterface>('User', userSchema);

  const user = await User.create({ name: 'John', age: 25 });
  const car = await Car.create({
    make: 'Toyota',
    model: 'Camry',
    year: 2020,
    owner: user._id
  });

  const populatedCar = await Car.findById(car._id)
    .populate<{ owner: UserObjectInterface }>('owner')
    .exec();

  if (!populatedCar) return;

  console.log(populatedCar.owner.name); // outputs John

  const depopulatedCar = populatedCar.depopulate();

  console.log(populatedCar.owner.name); // outputs undefined
  console.log(depopulatedCar.owner.name); // outputs undefined BUT throws type error on 8.3.1
}

main().then(() => {
  console.log('done');
});

Expected Behavior

The return value from .depopulate() method should be the depopulated type.

In the case of the reproduction script,

console.log(depopulatedCar.owner.name)

is expected to give a type error, because owner type is expected to be ObjectId

[vkarpov15]

With #14891 you'll be able to do doc.depopulate<{ user: ObjectId }>('user')