Bug Report

🔎 Search Terms

Posted question to StackOverflow:
Generic React/Typescript function has function in props but does not detect return type when param added
but it occurs to me this may be a bug!?

🕗 Version & Regression Information

• Tested in TypeScript 4.5.4

⏯ Playground Link

Playground link with relevant code

💻 Code

function simplified<T>(props: { generator: () => T, receiver: (t: T) => any }) {
}

function whatIWant<T>(props: { generator: (bob: any) => T, receiver: (t: T) => any }) {
}

function nonObject<T>(generator: (bob: any) => T, receiver: (t: T) => any) {
}

simplified({ generator: () => 123, receiver: (t) => console.log(t + 2) })
whatIWant({ generator: (bob) => bob ? 1 : 2, receiver: (t) => console.log(t + 2) })
nonObject((bob) => bob ? 1 : 2, (t) => console.log(t + 2))

🙁 Actual behavior

The whatIWant function is showing an error because it thinks t is unknown type.

The other two (simplified and nonObject are correctly seeing t as a number type.

🙂 Expected behavior

Above code (all three cases) should have no errors.

I'm particularly confused by the difference between simplified and whatIWant. Why is this correct behaviour, or is it a bug?