JavaScript: default parameter causes type to be incorrectly inferred

From https://github.com/Microsoft/vscode/issues/62013

TypeScript Version: 3.2.0-dev.20181027

Search Terms:

Code For the javascript:

var SomeObject = {
    SomeFunction: function (SomeInput) {
        return SomeInput * 2;
    },
    SomeOtherFunction: function (SomeOtherInput, SomeOptionalInput = SomeObject.SomeFunction(2)) {
        return SomeOtherInput * SomeOptionalInput;
    }
};

SomeObject

Hover over SomeObject

Bug: Type is any. If the default parameter is removed then the type is correct

[weswigham]

It looks like something causes us to pull on the signature type early which, with the initializer, depends on the object type itself and causes it to get marked as circular, specifically with noImplicitAny on, we get the

'SomeObject' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.

error. Thing is, if you wrote the same thing in a more namespace-y way:

namespace SomeObject {
    export function SomeFunction(SomeInput) {
        return SomeInput * 2;
    }
    export function SomeOtherFunction(SomeOtherInput, SomeOptionalInput = SomeObject.SomeFunction(2)) {
        return SomeOtherInput * SomeOptionalInput;
    }
}

we do waaaaaaaay better, even though the two are pretty much equivalent in this case. I think that technically this is working as intended; but for the sake of our JS users, we could do better here.

[weswigham]

Errr… noImplicitAny? noImplicitThis?