`mongoose.InferSchemaType` does not correctly infer nullable arrays

Prerequisites

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

Mongoose version

6.5.5

Node.js version

16.15.1

MongoDB server version

5.0.12

Description

When working with Mongoose schemas involving array fields that are nullable, mongoose.InferSchemaType does not seem to correctly infer the schema type. The notion of optionality does not seem to be reflected.

Steps to Reproduce

Let’s suppose we create a Mongoose schema with 2 fields of 2 different types, one being an array of strings, the other an array of objects, both optional.

const TestSchema = new mongoose.Schema(
  {
    comments: { type: [String], default: () => undefined, required: false },
    reference: {
      type: [
        {
          type: { type: String, required: false },
          value: { type: String, required: false },
        },
      ],
      default: () => undefined,
      required: false,
    },
  },
  {
    collection: 'tests',
    timestamps: false,
  },
);

export type TestType = mongoose.InferSchemaType<typeof TestSchema>;

In TestType, the notion of optionality of our fields seems to be lost:

The problem is the same if we replace default: () => undefined by default: () => null.

If we just try default: undefined or default: null, another problem appears:

Perhaps there is a misunderstanding/error on my side in defining the schema. If this is the case, I would be happy to receive your advices. Otherwise, it must be a bug? 🐛

Expected Behavior

{
    comments?: string[];
    reference?: {
        type?: string;
        value?: string;
    }[];
}

[Uzlopak]

@mohammad0-0ahmad

[vkarpov15]

Confirmed that this issue still happens if strict: true isn’t set. Following script fails to compile without --strict. We’re looking into that to see if we can fix it.

import mongoose from 'mongoose';

const TestSchema = new mongoose.Schema(
  {
    comments: { type: [String], default: () => undefined, required: false },
    reference: {
      type: [
        {
          type: { type: String, required: false },
          value: { type: String, required: false },
        },
      ],
      default: () => undefined,
      required: false,
    },
  },
  {
    collection: 'tests',
    timestamps: false,
  },
);

export type TestType = mongoose.InferSchemaType<typeof TestSchema>;
const doc: TestType = { comments: undefined };