Apply inference in method arguments when using a discriminator #60366

🔎 Search Terms

github: interface infer
github: interface discriminator
github: interface discriminator method
google: typescript method gets the result of another optional method
google: typescript one property sets the type of another property
google: typescript one property sets the type of the next property

🕗 Version & Regression Information

Happens from 3.3.3 (Removing NoInfer) up to the nightly version.

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/JYOwLgpgTgZghgYwgAjgHgEoFEDKBGAPmQG8BYAKGSuRgFcQE8AKASgC5t8BuC6m+hACYA-GxAQAbtB6VqdBgGYmAEzhg4bAHIB7AJIgY0TLkLsJ24MpkBfCqEixEKAEbH8AGmSdBRMrKryjKwcJjJ8gYIqaho6+oZQbqYhOIJhcgJKqupaegZG3gRmFlYUtuRgAJ4ADigAtsAAHomeBcgAvKiJRAA+yK6ceC24PjIUgWDA2iA0zV7DBFHZ9U0DQymFJBSlY0x+4QLMLJv+fMhQEGC0UNN4ggq81NbuDwECkVlwR3unVOeX18gAES3BSAl7IJ7gwKZaJfZAAenhyAACnAoHBahdoMgAOQfHHIYC1KoAG2ACGAYBJFWQAAs4ABnVDTHFwEAVAmVGoAOi2JzK1hYXCAA

💻 Code

interface a<RES1> {
    func1():RES1;
    func2?:never;
    func3(data:NoInfer<RES1>):void;
}
interface b<RES1, RES2> {
    func1():RES1;
    func2(data:NoInfer<RES1>):RES2;
    func3(data:NoInfer<RES2>):void;
}
type mix<RES1, RES2> = a<RES1> | b<RES1, RES2>;

function f<RES1, RES2>(data:mix<RES1, RES2>) {

}
f({
    func1() {
        return 123
    },
    func2(data) {
        return "123"
    },
    func3(data) { // Parameter 'data' implicitly has an 'any' type.

    }
});

🙁 Actual behavior

It happens that func3 argument is not properly inferred as is trying to infer the a interface, although it doesn't apply because the requirement for that interface is to explicitly not have a func2 property.

If I change both func3 arguments to the same type (RES1 for example) it works, so it is actually getting both interfaces.

🙂 Expected behavior

I guess that it should first get the applicable interfaces, and then try to infer the values depending on the applicable interfaces only.

Additional information about the issue

Still, I'm not sure about this approach. What I want is to have a func3 method that receives the result of func1 or func2 depending if func2 exists or not, like a transformer, but everything inside the same interface.