Make ParameterDecorator and the like generic

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.

Start by locating the ParameterDecorator definition and the compiler checks for applying parameter decorators. Compare the issue's number and string examples to the current behavior, then determine how generic parameter types should be represented and validated. Done means valid decorator applications are accepted and mismatched parameter types are rejected with appropriate tests.