Unexpected return type of overloaded function

[rotu]

🔎 Search Terms

overload, multiple call signature

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play/?target=99&jsx=0&ts=4.8.4&q=5#code/JYOwLgpgTgZghgYwgAgHIHswG8BQz-IAUAHgFzIBG66ANhHCAJTlW30gDceBJ58NAZwjNkYKAFcIXAkTKiJwvnEFTu+XpWp0GI1ts44AvjhwATCAhpwoKAG7XkITKQxgcCdCAFhHmAIIgAJ7IALy+YIRikshwAjFBjMgA9Eny0QCEAPxZOCkyAHqZQA

💻 Code

interface Not{
    (x: boolean): boolean;
    (x: false): true;
    (x: true): false;
    (x: boolean): boolean;
}

declare var not:Not
const notAny = not(true as any) // true !?!?
//    ^?

🙁 Actual behavior

The type of notAny is inferred as true, the return type of the second overload call signature.

🙂 Expected behavior

The type of notAny should infer to boolean, as the first applicable signature without assignment to any (described as the expected behavior here)

Alternately the type of notAny should infer to boolean as the last signature (and thus the type ReturnType<Not>).

Additional information about the issue

Variation of this issue originally reported in #59064.

[MartinJohns]

This still sounds like a duplicate of #39833.

[rotu]

This still sounds like a duplicate of #39833.

Looking at that issue again, I think it is.

I interpreted the referenced comment to mean "assignment to a parameter of type any" not "assignment from an argument of type any", so I may have missed that.

as the first applicable signature without assignment to any (described as the expected behavior here)