Bug: 5.27.0 regression: @typescript-eslint/no-unused-vars wrongly reports the jsxFactory set in tsconfig.json

[lydell]

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• I have tried restarting my IDE and the issue persists.
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Issue Description

I use Preact and have this in my tsconfig.json:

    "jsx": "react",
    "jsxFactory": "h",
    "jsxFragmentFactory": "Fragment"

I use it like so:

import { h, Fragment } from "preact";

export default function MyComponent() {
  return <><h1>Hello, world!</h1></>;
}

It used to result in no errors. With version 5.27.0, it reports h and Fragment as unused.

I’ve searched through the issue tracker, and also in TypeScript’s and Preact’s issue trackers, but couldn’t find anything. I apologize if I missed something, or this is a misunderstanding on my side that just happened to work before!

Reproduction Repository Link

https://github.com/lydell/typescript-eslint-preact-issue

Repro Steps

1. clone the repo
2. npm ci
3. npm test

Versions

package	version
@typescript-eslint/eslint-plugin	5.27.0
@typescript-eslint/parser	5.27.0
TypeScript	4.7.3
ESLint	8.17.0
node	18.1.0

[bradzacher]

I can check later today when I'm at my laptop, but I think all you need is to set parserOptions.jsx = true

We probably should remove that restriction though as we don't use that anywhere else.

[lydell]

I can confirm that adding this to my ESLint config makes it work:

"parserOptions": {
  "ecmaFeatures": {
    "jsx": true
  }
}

[bradzacher]

For this issue we want to remove the requirement for the parserOptions.ecmaFeatures.jsx option to be set for the automated pragma resolution. Should be a simple change!

[Solo-steven]

Hi @bradzacher , I am new there and I want to take this issue. After some research, I find two solutions,
The first is to make jsx option fallback to true, which would make the parser automatically resolve jsx pragma.

The second solution is to emit the if statement before pragma resolves, but this method would make the parser resolve jsx pragma even if jsx option is false. So I think the first solution is a better one.

looking forward to your response!

[bradzacher]

Given that JSX pragma and factory are only used by the tooling if we encounter JSX syntax in the code - there's not really any cost to us resolving the config even if jsx == false.

In fact it's better if we do that because in a lot of cases we actually ignore the jsx setting!

So let's go with the second solution of just removing the parserOptions.jsx check entirely.