Typescript: Wrong return type when using lean in different way

[GuiHash]

Prerequisites

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

Mongoose version

6.X.X - 7.X.X

Node.js version

at least 16

MongoDB server version

at least 4

Typescript version (if applicable)

4.7 - latest

Description

The return type of

const a = await Model.findById('my-id', undefined, { lean: true })

is the same as

const a = await Model.findById('my-id')

it's:

// ^? const a: (mongoose.Document<unknown, {}, { name: string; }> & { name: string; } & { _id: mongoose.Types.ObjectId; }) | null

Steps to Reproduce

See ts playground

Expected Behavior

The return type should be the same as

const a = await Model.findById('a').lean()

it's:

// ^? const a: (mongoose.FlattenMaps<{ name: string; }> & { _id: mongoose.Types.ObjectId; }) | null

[vkarpov15]

We'll investigate and see if it is reasonably possible to fix. As a workaround, use Model.findById('a').lean().

[sspenst]

For reference, I just updated from mongoose 7.4.2 to 7.6.2 and had to change every occurrence of:

TModel.findOne<T>({}, {}, { lean: true })
TModel.find<T>({}, {}, { lean: true })

to:

TModel.findOne().lean<T>()
TModel.find().lean<T[]>()

sspenst/thinky.gg@8c3c744