Another narrowing bug with `{}`

[chancancode]

TypeScript Version: playground

Code

type unknown = {} | undefined | null | void;

interface Dict {
 [key: string]: unknown;
}

function isDict(value: any): value is Dict {
 return value !== null && value !== undefined;
}

function any(): any {
}

let notSure: unknown = any();

if (isDict(notSure)) {
 notSure['foo']; // <- turn on strict mode to see error, `notSure` is `{}`
}

Expected behavior:

notSure is Dict after the narrowing

Actual behavior:

notSure is {} after the narrowing

Playground link

[chancancode]

This is only a problem with {} involved – the definition suggested here works

[RyanCavanaugh]

A union with { } in it will eagerly collapse to { } as soon as it's examined by the type system; a union like this should never be written down on purpose. Did you mean unknown = object | undefined | null | void ?

[chancancode]

We have switched to unknown = object | number | string | boolean | symbol | undefined | null | void as per #18196, just thought we would report this in case it is a bug that is not already known.

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.