What version of Oxlint are you using?

1.64.0

What command did you run?

oxlint

What does your .oxlintrc.json (or oxlint.config.ts) config file look like?

Reproduces without a config file (requires no-unused-var to be enabled)

What happened?

Code:

export function foo(a: unknown): a is string {
  return true;
}

oxlint flags a as unused despite its use in return type (a is string).

  ⚠ eslint(no-unused-vars): Parameter 'a' is declared but never used. Unused parameters should start with a '_'.
   ╭─[test.ts:2:21]
 1 │ 
 2 │ export function foo(a: unknown): a is string {
   ·                     ┬
   ·                     ╰── 'a' is declared here
 3 │   return true;
   ╰────
  help: Consider removing this parameter.

I am not sure if this should be treated as a bug; it's totally understandable to flag a as unused particularly because you can't write meaningful code without using such a parameter inside function body.

I'm reporting this anyway because it diverges from ESLint behavior and I encountered this while migrating from ESLint.

Thank you for the great tool. It's fast 🙂