Bug Report

🔎 Search Terms

variance, conditional, subtype, limit

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about variance and conditionals.

⏯ Playground Link

Playground link with relevant code

💻 Code

interface Base {
    base: unknown;
}

interface Sub extends Base {
    sub: unknown;
}

function transform<T extends Base>(t: T): T extends Sub ? Sub : T {
    return t;
}

🙁 Actual behavior

"Type 'T' is not assignable to type 'T extends Sub ? Sub : T'."

🙂 Expected behavior

No errors. Either T extends Sub, and so is assignable to it, or it doesn't, and so is assignable to itself.