Typescript: Error Handling Middleware callback function params are implicitly set to 'any'.

Prerequisites

• I have written a descriptive issue title

Mongoose version

6.6.7

Node.js version

18.11.0

MongoDB version

6.0.1

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

12.6

Issue

I’m following this documentation [Error Handling Middleware](https://mongoosejs.com/docs/middleware.html#error-handling-middleware), and TypeScript does not infer the error middleware function arguments if three parameters are given.

userSchema.post('save', function (error, doc, next) { <------ All params implicitly has an 'any' type.
  if (error.name === 'MongoServerError' && error.code === 11000) {
    next(new Error('There was a duplicate key error'))
  } else {
    next()
  }
})

I know it is possible to set those types explicitly. However, it will lead to a bunch of boilerplate code, which should be inferred from ErrorHandlingMiddlewareFunction type.

My tsconfig.json:

{
  "compilerOptions": {
    "target": "es6",
    "module": "commonjs",
    "rootDir": "src",
    "outDir": "dist",
    "lib": [
      "es6"
    ],
    "removeComments": false,
    "strict": true,
    "declaration": true,
    "declarationDir": "types",
    "skipLibCheck": true,
    "esModuleInterop": true
  },
  "include": [
    "src",
    "test"
  ],
  "exclude": [
    "node_modules"
  ]
}

[vkarpov15]

See #12723, you’ll have to do the following in 6.8 to help TypeScript out:

userSchema.post('save', { errorHandler: true }, function (error, doc, next) {
  if (error.name === 'MongoServerError' && error.code === 11000) {
    next(new Error('There was a duplicate key error'))
  } else {
    next()
  }
})

[vkarpov15]

It looks like TypeScript struggles to distinguish between (this: ThisType, res: ResType, next: CallbackWithoutResultAndOptionalError) => void and (this: ThisType, err: NativeError, res: ResType, next: CallbackWithoutResultAndOptionalError) => void, maybe because it doesn’t assume that number of arguments can be used to distinguish between 2 function overloads. If I delete the non-error-handling post() definitions, this code compiles fine.

We’re probably going to have to add a new feature or way to define error handling middleware that TypeScript can distinguish.