ObjectOmit narrows any type to {}

[OliverJAsh]

import { ObjectOmit } from 'typelevel-ts';

type OmitUser<T> = ObjectOmit<T, 'user'>;

// Type is `{}`, expected `any`
type Result = OmitUser<any>;

Is there any way around this?

[KiaraGrouwstra]

hm. when removing string-based keys, doesn't it make sense that the output would be some kind of object?

[OliverJAsh]

I'm not sure 🤔

For context, this behaviour is causing issues for me when I'm trying to use the withDefaults HOC, where the composed component doesn't have its prop types defined yet:

class Foo extends React.Component<any> {}

const DefaultedFoo = withDefaults(Foo, { baz: 1 });

// Unexpected error: Property 'bar' does not exist on type 'IntrinsicAttributes & Pick<any, never> & Partial<{ baz: number; }> & { children?: ReactNode; }'.
<DefaultedFoo bar="foo" />;

This is because ObjectDiff uses ObjectOmit, and in this case it resolves to Pick<any, never>.

Although I am able to workaround the issue by widening the default props object to any:

type Props = any;
class Foo extends React.Component<Props> {}

const defaults: Props = { baz: 1 }
const DefaultedFoo = withDefaults(Foo, defaults);

<DefaultedFoo bar="foo" />;

[KiaraGrouwstra]

Makes sense. {} admittedly is rather restrictive (no keys known to exist), whereas the intent in any was obviously to make it less restrictive, which seems to backfire now. Guess that does seem unfortunate.

[amir-arad]

I think design decisions in typescript made a turn for the worse :(
microsoft/TypeScript#20247

[IanYates]

Would Conditional Types - microsoft/TypeScript#21316 - help here?

[OliverJAsh]

@IanYates Maybe! Could we do something like type OmitUser<user> = T extends any ? any : ObjectOmit<T, 'user'>?

[KiaraGrouwstra]

I fear all types would extend any -- in that event I'd suggest flipping the check to any extends T ? -- I suppose that would actually hold only if T were to be any as well.