Typescript - .lean output is missing types

[BB-19]

Prerequisites

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

Mongoose version

8.9.5

Node.js version

23.5.0

MongoDB server version

6

Typescript version (if applicable)

5.7.2

Description

There has been a breaking change that causes an invalid type with the .lean output.
Previously, the types were properly inherited but this broke after 8.6.4. The issue still exists with the newest mongoose version 8.9.5.

Last working version: 8.6.4

See example to reproduce.

Steps to Reproduce

1. Modify Typescript example from Mongoose docs as follows:

import { Schema, model, connect } from 'mongoose';

// 1. Create an interface representing a document in MongoDB.
interface IUser {
   name: string;
   email: string;
   avatar?: string;
}

// 2. Create a Schema corresponding to the document interface.
const userSchema = new Schema<IUser>({
   name: { type: String, required: true },
   email: { type: String, required: true },
   avatar: String,
});

// 3. Create a Model.
const User = model<IUser>('User', userSchema);

run().catch((err) => console.log(err));

async function run() {
   // 4. Connect to MongoDB
   await connect('mongodb://127.0.0.1:27017/test');

   const queriedUser = await User.findOne({ name: 'Bill' }).exec();
   queriedUser?.email // string

   const queriedUserLean = await User.findOne({ name: 'Bill' }).lean();
   queriedUserLean?.email // error in newer mongoose versions (but works in 8.6.4)
}

3. Test with 8.6.4 -> No error
4. Test with newer mongoose -> Type error when using .lean()

Expected Behavior

Types should be inherited like in 8.6.4 when using .lean()

[bartlomiejwulff]

I‘m facing the same issue

[vkarpov15]

I'm unable to repro this, TypeScript playground shows no errors: https://www.typescriptlang.org/play/?#code/JYWwDg9gTgLgBAbzgZQMYAsCmICGAaOECAE0wBsDUIA7azVeAXzgDMoIQ4ByI6gcwgQAzpi4BuAFASA9NLgBGAHRwAwlEw4YmODmpxg1LVBY5U29WHUjDBvjrjEIqAK4hMh-XoCyNAQBEAIUUJAyMTMzgASQBVEShECTgk6hw3AC44IRgoW0kkuGwcYDIMrJz+PKScADdNHCgAflLs3IlGKVk4ACZlNQ0tezQsXDgqKCtIamJbOBgIWawHJ1d3eFDMY1NMYKpqLLhnOKHCuABeODoAdxQMQoAeGLiAPgAKBETk1MwMpBgATzA3xQLX4BHUAEdnMB1MQMtlnNpGHgPgVcMUfrMAUDkCC+GDMJDoZhYbMoAi4EiUTU6lAMjjyni2gBKSQyOQAZl66k02hwcB8pDIOxo+1iGzOhBI5AeYqgry4sq4BEOG2OuBZUjJ1BeTMUqE0GBeLw2UCZZyeoxFEDI2zIED4xvGTI1EhwQj+1FQrGcnpgwBocC1OoS+U6ABZejQ6AxZvMfPwIIEqZcivBdtGYC8eL4SAAjNKyeRdADsigADOXFPI0iWy-Ji9ItFkuC78rt9pCNsBibKJTgU8B4LLFCwDMQAPJ0N4XL4ZLgBYpkLgU3WYAAe9B1lTgnZyPbiDUUhWKcE6ZVsUjbIvgu+7xFlABkNHpzv3U3Bh6OppPMNOUuluAXMglxXRQbV0LcUVvfcNifXRD2PMhTzkE1oE8C5MEucVeAEYRtGqDYhH9PY4BeXNnHgS5oAAayEdCAA5FAANkUMMmTaIA and running locally doesn't have any errors either

$ ./node_modules/.bin/tsc --strict gh-15189.ts 
$ head ./node_modules/typescript/package.json 
{
    "name": "typescript",
    "author": "Microsoft Corp.",
    "homepage": "https://www.typescriptlang.org/",
    "version": "5.7.3",
    "license": "Apache-2.0",
    "description": "TypeScript is a language for application scale JavaScript development",
    "keywords": [
        "TypeScript",
        "Microsoft",
$ 

Can you please provide more detailed repro instructions, like what your tsconfig.json looks like and how you're running tsc?

[BB-19]

Seems like this is happening when the tsconfig is missing "node" under compilerOptions.types.
Not sure why it worked in the past and why it works with .exec with the same tsconfig but issue was solved for me by adding the node types.

Closing issue. Feel free to re-open if this is a bug.