Add a @Deprecated decorator for deprecation warnings

I’m submitting a…

[ ] Regression 
[ ] Bug report
[x] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

At the moment there is no normalized way to add a deprecation warning of a functionality

Expected behavior

There should be a @Depreacted(message?: string) decorator which logs a deprecation warning when calling the function.

E.g.

class MyService {
  
  @Deprecrated('The noGood method will be deprecated in the next major release. Please use the reallyGood method of the MyService instance')
  public noGood() {
    // my super old function
    console.log('No good :(');
  }

  public reallyGood() {
    console.log('Wow this function is so much nicer');
  }
}

[...]

this.myService.noGood(); 

// prints out:
// Deprecation warning: The noGood method will be deprecated in the next major release. Please use the reallyGood method of the MyService instance
// No good :(

What is the motivation / use case for changing the behavior?

It would be useful for a developer to add a clear deprecation warning for a function. This can also be useful for NestJS or its additional modules.

I think it should be part of Nest, so it can be integrated with the already existing logger.

Other

Deprecating before runtime (Intelisense) is currently not possible with TypeScript. See issue here https://github.com/Microsoft/TypeScript/issues/390

[lazarljubenovic]

I’d expect @Deprecated as a decorator on a controller method to include deprecation warning in the Response, not the log it. Like, deprecating an API method (endpoint), not a method from code. For deprecating methods, TSDoc’s /** @deprecated */ is an already established way. Although, I agree, not runtime-specific – but then again why would Nest provide a runrime deprecation warning for a custom method in code? It seems like a job for a completely separate general TypeScript decorator (there’s probably something on npm already).

One of the ideas is to use 299 code for a deprecated endpoint, which could be what this decorator would do by default.

[BrunnerLivio]

@lazarljubenovic I see you point, I think you’re right. Looking through the source code of NestJS it seems like it is used by deprecated npm package. The only downside is with this approach, the package is probably not integrated with the NestJS logger, so it will be harder for the user to suppress such warnings. But that is a different topic. I’ll close this issue now. I encourage you (@lazarljubenovic) to create a new issue for controller deprecation functionality.