[no-unused-vars] False positive for unused vars inside decorator arguments

[ridaamirini]

From eslint/typescript-eslint-parser#445

What code were you trying to parse?

import { Component, Vue } from 'vue-property-decorator';
import HelloWorld from './components/HelloWorld.vue';

@Component({
  components: {
    HelloWorld
  }
})
export default class App extends Vue {}

What did you expect to happen?

With eslint-plugin-typescript's typescript/no-unused-vars rule enabled, should lint without errors.

What happened?

error: 'HelloWorld' is defined but never used (no-unused-vars)

It looks like the expression in a decorator's argument position is not taken into context when determining unused vars. Also, when using eslint --fix, code inside decorator arguments are sometimes not formatted correctly.

[SunshowerC]

So could anyone fix it ?

[gwardwell]

I'm seeing this issue as well. Is there any progress on a fix?

[bradzacher]

https://astexplorer.net/#/gist/9f8a50b0db8e4f6eb6a4232cb3bf4160/618c7989605019cdd3a3b8d023cb8c6fe47a837f

const foo = '';

@deco({
  foo
})
export default class App {}

@deco({
  foo
})
export class App {}

Looking at the AST and comparing it to the markDecoratorAsUsed function, it looks like it was never built to handle decorator arguments.

Having a look, this will be fixed by the new visitorKeys config that the parser added in v20.
So this should be fixed by #166