Inference from result of generic function no longer produces a union

[dragomirtitian]

🔎 Search Terms

function inference

🕗 Version & Regression Information

• This changed between versions 5.9 and 6.0-rc

⏯ Playground Link

Playground Link

💻 Code

declare function deepEqual<T>(actualValue: T, expectedValue: T, message?: string): void;
declare function compact<T>(obj: T): T 
// Error
deepEqual(compact({ a: "hello", b: undefined }), {
    a: "hello",
});
// Ok
deepEqual({ a: "hello", b: undefined }, {
    a: "hello",
});

🙁 Actual behavior

First call fails. T for deepEqaul is inferred to { a: string, b: undefined;} instead of { a: string; b: undefined; } | { a: string; b?: undefined; } as it is for the second call that succeeds. In 5.9, T is inferred to { a: string; } which is not really great either.

🙂 Expected behavior

Both calls should pass type checking

Additional information about the issue

No response

[Andarist]

bisects to #62502