Before You File a Bug Report Please Confirm You Have Done The Following...

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I have searched for related issues and found none that matched my issue.
• I have read the FAQ and my problem is not listed.

Playground Link

https://typescript-eslint.io/play/#ts=5.4.3&showAST=scope&fileType=.tsx&code=C4TwDgpgBAwg9gWzAV2BAPAQQHxQLxSZQQAeaAdgCYDOUAYsuQMbACWc5UA-IVAFxQA3lADaAaSitOAawgg4AM0IBdAfCSoMmcctwBfANwAoI6EhQAogEdkAQwA26ABoAaKAE1ceI1CgAKdAAVAEZsPwBKfFwQ4jIIKlp1FDRnXB5g-igAJkjSChooIKywyLxorNj8xMRkjE9uKAyBCp5gACdkaAEFB2oIYyMgA&eslintrc=N4KABGBEBOCuA2BTAzpAXGYUACAXAngA4oDG0AlobgLQrzkB2uA9AwPbWwMOIkrIBDaPmoFi1QkIEBbRLkTRUGSAuhtokAL4hNQA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false

Repro Code

type Compute<A> = A extends Function ? A : { [K in keyof A]: Compute<A[K]> };

type Equal<X, Y> =
  (<T1>() => T1 extends Compute<X> ? 1 : 2) extends <T2>() => T2 extends Compute<Y> ? 1 : 2 ? true : false;

ESLint Config

module.exports = {
  "rules": { "@typescript-eslint/no-unnecessary-type-parameters": "error"}
}

tsconfig

{
  "compilerOptions": {
    "strictNullChecks": true
  }
}

Expected Result

I wouldn't expect this to give any errors. As far as I can tell, there's no way to achieve the same functionality without adding <T1> and <T2>.

Actual Result

I'm getting two errors (one for each T):

• Type parameter T1 is used only once.ESLint @typescript-eslint/no-unnecessary-type-parameters
• Type parameter T2 is used only once.ESLint@typescript-eslint/no-unnecessary-type-parameters

Additional Info

In all honesty, I don't understand how that Equal utility type works. But I know it does: it returns true if X and Y are assignable to one another (and if one is any, only if the other one is any as well). I have been using it in my codebase for a while.