Make ParameterDecorator and the like generic

[entropitor]

lib Update Request

Missing / Incorrect Definition

ParameterDecorator is currently not generic, it can be attachted to any parameter. However, when a decorator is used for e.g. Dependency Injection purposes, some decorators require the type of the parameter to be consistent with the type of the decorator

Sample Code

E.g. we want this to work

class MyController {
  requestThings(@UserId() userId: number): Thing[] { return [] }
}

But this to fail:

class MyController {
  requestThings(@UserId() userId: string): Thing[] { return [] }
}

(as userId will be a number, not a string so the injection should ideally not be possible (at compile time)

Currently UserId is done more or less this way:

const UserId = (): ParameterDecorator => (target, key, index) => { 
  // do stuff
}

while I'd like to add number to ParameterDecorator:

const UserId = (): ParameterDecorator<number> => (target, key, index) => { 
  // do stuff
}

and I'd like typescript to check this when applying a decorator.

[gastonmorixe]

This is really important, specially in NestJS where decorators are used broadly. I'd love to know event have to specify the type at all in the param.

https://docs.nestjs.com/custom-decorators#param-decorators

import { createParamDecorator, ExecutionContext } from '@nestjs/common';

export const User = createParamDecorator<unknown, ExecutionContext, UserEntity>(
  (data: unknown, ctx) => {
    const request = ctx.switchToHttp().getRequest();
    return request.user;
  },
);

@Get()
async findOne(@User() user) { // user should automatically be typed as UserEntity
  console.log(user);
}

[ianzone]

Mark nestjs/nest#11414