[deprecation] Warns when deprecated APIs are used.

[htho]

Repro

{
  "rules": {
    "@typescript-eslint/deprecation": ["warn"]
  }
}

// CASE 1: for functions
/** @deprecated use f2 instead */
function f1(): void {return;}
function f2(): void {return;}

f1(); // WARN: "f1 is deprecated: use f2 instead

// CASE 2: for interfaces
interface Test {
  /** @deprecated use b instead */
  public a?: string;
  public b?: string;
}

const x: Test = {
  a: "foo"; // WARN: "Test.a is deprecated: use b instead
}

Expected Result
In both cases there should be a warning, that the function or property are depricated.

Actual Result
The @depricated comments are ignored.

Additional Info
There is a TSLint Rule: deprication and a long discussion at the TypeScript Bugtracker

I did not check the implementation for TSLint, but there are many things to consider. They should be configurable.

1. For interfaces a depricated property must be optional (otherwise one could not not use the property)
2. There should be a warning if a private or protected property is marked as depricated. (at least private properties should be updated as soon as a property is depricated)
3. A @depricated tag must be followed by an explanation and/or alternative.

[ark120202]

Related: https://github.com/SonarSource/SonarJS/issues/1432, SonarSource/SonarJS#1715

Later we can contribute this rule to typescript-plugin for eslint.

[gund]

Now that this rule was implemented and merged in SonarJS - are there any plans to bring this to typescript-eslint?

[bradzacher]

We don't have any. If someone wants to PR it, we would be happy to review it.

[gund]

I believe it's just a matter of copy-pasting this rule from sonarjs repo?

[bradzacher]

It's not quite as simple as a copy paste job, as that code has its own licence.
Someone needs to discuss with the maintainers, and make sure they're okay with the port.

Also, the code would have to be updated to fit our coding standards in this repo, as the style is reasonably different.

[gund]

Well SonarJS repo uses LGPL which allows any redistribution of source code but under either GPL or LGPL licence. Which is not gonna work because this repo is using BSD like license.

However, it is possible to port that rule into eslint plugin (say eslint-plugin-deprecation) and licence it under LGPL and then use it here as external library.

Maybe it makes more sense to just create another repo for this rule?

[bradzacher]

If someone wants to port the rule to an independent eslint plugin, feel free!
If someone wants to simply document how to use the sonar rule, they can do that instead.
If someone wants to independently implement the rule based on tslint's implementation, they can do that too.

[gund]

Alright, I've ported the rule into separate plugin https://github.com/gund/eslint-plugin-deprecation

[bradzacher]

happy if you update the docs to point at your plugin, and then we can consider this closed.
https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/ROADMAP.md#maintainability

(note the docs currently point at an eslint-plugin-import rule, which is not as good as a rule using typescript types, like your ported rule does)

[webmaster128]

Thank you @gund!

If someone stumbles upon this, I think t would still be cool to have a port of the tslint implementation (as suggested by @bradzacher) in this repo due to licensing reasons and for fewer dependencies.