Function property in union does not get parameter type inferred from result of type narrowing

[dyantako]

🔎 Search Terms

type narrowing inferred function parameter union discriminant

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.9.3&ssl=17&ssc=52&pln=1&pc=1#code/JYOwLgpgTgZghgYwgAgGIHt3IN4ChnIBucANgK4QBcyAzmFKAOYDc+tEYAaqRdQBTFyVWvSYBKZAF4AfEXTAAJqwC+uXKEixEKAEJwoONoN7IQZALYAjaKwI0O3If2PCzV6BJlzFKtWACeAA4oAPKBYMDoIDRSaJjIAD7IelCsuDBkIAgRUcgwIHzo4ZHR1GE50RJ4BFAcZFAgpmQkJL7pBdhEPMIARD0ANOxc3fwQnrIIUTToJBAAdCTojHxjyMpizEA

💻 Code

interface Foo {
  value: string;
  setValue: (value: string) => void;
}

interface Bar {
  value: number;
  setValue: (value: number) => void;
}

type Options = Foo | Bar;

function fn(options: Options) {
  return null;
}

fn({ value: "", setValue: (e) => console.log(e) });

🙁 Actual behavior

The e parameter of setValue is inferred as any rather than string, despite value being a string which means Foo is the only valid type.

🙂 Expected behavior

setValue here should have e inferred as a string

Additional information about the issue

No response