@‌deprecated JSDoc tag

[DickvdBrink]

It would be cool to annotate a method or property with a deprecated attribute

Proposal

If a warning could be issued when using a deprecated method or property it is easier to upgrade to a newer library version (only when the definitions are up to date of course)

Syntax: Same as JSDoc, a simple comment

/**
 * @deprecated Use other method
 */
public foo() {
}

If supported in .d.ts files, this would really help with upgrading to a newer version.

[RyanCavanaugh]

How would this flow through the type system?

interface X {
    /*
     * @deprecated Use DoOtherThing instead
     */
    doThing(): void;
}

interface Y {
    /*
     * Still supported
     */
    doThing(): void;
}

class Z implements X, Y {
    doThing() {}
}

var g = new Z();
g.doThing(); // OK? Not OK?

Presumably you'd be able to mark a single overload (but not others) as deprecated; would referencing (but not calling) a function with a deprecated overload be an error?

[DickvdBrink]

Hmz, tricky question.. didn't thought about this one actually.

Maybe it is only an error in this case when calling it like this:

var x: X = new Z();
x.doThing() // it selected to @deprecated methode so error

var y: Y = new Z();
x.doThing() // still supporter, no error

Not really sure though, feels a bit error prone...

[JustinBeckwith]

C# will allow what you've written above, because it does not react to [Obsolete] attributes on interfaces - only base class implementations. Given the lack of multiple inheritence, this isn't really an issue. Here's how it's handled in C#:

class Program
    {
        static void Main(string[] args)
        {
            var x = new Zoo();

            // doThing is allowed, even though it is obsolete on interface X
            x.doThing();

            // doStuff is not allowed. It is not obsolete on the interface, but is obsolete on the base class. 
            x.doStuff();
            Console.Read();

        }
    }

    interface X
    {
        /// <summary>
        /// 
        /// </summary>
        [Obsolete("boo", true)]
        void doThing();
    }

    interface Y
    {
        void doThing();
        void doStuff();
    }

    class Zoo : ZooBase, X
    {
        public void doThing()
        {
            Console.WriteLine("boo");
        }

        [Obsolete]
        public override void doStuff()
        {
            Console.WriteLine("boo");
        }
    }

    abstract class ZooBase
    {
        [Obsolete("boo", true)]
        public abstract void doStuff();
    }

[mhegazy]

I think this is fair. the class provided a re-declaration of the method. if you were to use the interface directly you would get an error:

var g = new Z();
g.doThing(); // OK, this is the class definition of doThing()

var e: X = new Z();
e.doThing(); // Error, X.doThing() is deprecated.

Now consider this:

interface Person {
    name: string;

    /** @deprecated use birthDate instead */
    age?: number;

    birthDate?: Date;
}

declare function doStuff(p: Person): void;

// should calling doStuff with age instead of birthDate be an error:

doStuff({
    name: "Joe",
    age: 25          // Error?: Person.age is depreciated
});

if the answer is yes, then the above example should be an error on the extends clause, prohibiting the implementation of a depreciated method on the interface.

it also means you can not depreciate a non-optional member of an interface, cause how else would you use it.

[louy]

I believe this shouldn't cause an error but rather a warning.
For the situation @RyanCavanaugh mentioned, a function would only be deprecated if there doesn't exist any non-deprecated implementation.
As for implementing an interface-deprecated method in a class, you should get a warning once in the class implementation, not each time you're calling the method.

interface IX {
  @deprecated
  function doSomething(): void;
}

class X implements IX {
  function doSomething(): void; // Warning: IX.doSomething is deprecated

  @deprecated
  function doSomethingElse(): void;
}

const x = new X();
x.doSomething(); // Ok...
x.doSomethingElse(); // Warning: X.doSomethingElse is deprecated

[kitsonk]

That syntax collides with decorators. 😦

Considering this hasn't seen any action in a long time, and now that the compiler parses and integrates JSDoc, it could in theory understand and warn on /* @depecrated */ JSDoc, but is there yet the concept of warning in TypeScript or does it still consider everything an error?

Otherwise this should be the domain of something like tslint @adidahiya, thoughts?

[louy]

Yeah I know. I didn't know that the complier considered JSDoc comments. I thought we might have a reserved keyword or something.
I also think this is beyond the scope of tslint. Linting should be about coding style, not type checking.

AFAIK TS has no concept of warnings. In my opinion however, it should. Similar to ESLint's error/warning concepts.

[kitsonk]

Linting should be about coding style, not type checking.

I disagree... It should be about things deal with code quality, things that are syntactical errors. tslint and other linting tools do lots of quality checking, like unused variables, conditional assignments, switch statement drop through and defaults, etc.

In fact we draw the defenition from the UNIX lint tool which:

In computer programming, lint is a Unix utility that flags some suspicious and non-portable constructs (likely to be bugs) in C language source code; generically, lint or a linter is any tool that flags suspicious usage in software written in any computer language.

[louy]

@kitsonk okay I'm convinced. I'll open a new issue in tslint's repo then.

[felixfbecker]

I also think this is something that does not need a language feature, but belongs to documentation (jsdoc) and can be checked by something like tslint.