Typescript: schema type `required` argument, and `this` type

[AbdelrahmanHafez]

Prerequisites

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

Mongoose version

7.5.0

Node.js version

18.x

MongoDB server version

N/A

Typescript version (if applicable)

5.1.6

Description

In JS world, the document is accessible as an argument and as this for required functions.
In TS, however, we can not access those types.

Steps to Reproduce

The following test fails

function gh13797() {
  interface User {
    name: string;
    age: number;
  }

  const schemaWithArrowFunction = new Schema<User>({
    age: Number,
    name: {
      type: String,
      required(user) {
        expectType<User>(user);
        expectType<number>(user.age);
        return user.age > 30;
      }
    }
  });

  const schemaWithRegularFunction = new Schema<User>({
    age: Number,
    name: {
      type: String,
      required: function (user) {
        expectType<User>(user);
        expectType<User>(this);
        expectType<number>(user.age);
        expectType<number>(this.age);

        return user.age > 30;
      }
    }
  });
}

Expected Behavior

I expect it to pass.