Error on types when using multiple conditional properties about typescript

[jcalz]

The fact that this works sometimes is due to #30779, which is limited no matter what. It looks like if the discriminant is optional and the property is missing, #30779 doesn't kick in, and you get the same error you'd get when trying to equate a general union-of-objects with an object-of-unions. I don't know if they'll consider this a bug or just a limitation of the sort of thing handled by #30779.

[RyanCavanaugh]

Yeah, in general a single source type S isn't assignable to a target type T = T1 | T2 | T3 | Tn... just because a combinatorial explosion of S would ultimately result in every possible inhabitant eventually finding varying targets in T. There are exceptions, but this isn't one of them.

There's almost always a better way to write the target type; I'm not really clear on the intended semantics of the type as written here so can't advise much

[Arkellys]

If it helps to give a more concrete example, I need this for a React component with several props required or unnecessary depending on other props. For example:

<Chip
  removable={isRemovable} // Optional
  onRemove={noop} // Required if `removable` is `true`, unnecessary if removable is `false`
  label="test" // Required when no `children`, unnecessary when `children` is defined
>
  Test {/* Required when `label` is not defined */}
</Chip>

/**
 * @typedef {object} ChildlessProps
 * @property {string} label
 */

/**
 * @typedef {object} ParentProps
 * @property {any} children
 */

/**
 * @typedef {object} RemovableProps
 * @property {true} removable
 * @property {Function} onRemove
 */

/**
 * @typedef {object} StaticProps
 * @property {false} [removable=false]
 */

/**
 * @typedef {object} BaseProps
 * Other properties....
 */

/**
 * @typedef {BaseProps & (RemovableProps | StaticProps) & (ParentProps | ChildlessProps)} ChipProps
 */

I was handling these conditions with propTypes, but since prop types check will be removed on React 19 I decided to try and strengthen my JSDoc so that it could handle them instead (I don't use TS).

I'm not sure there is another way to write this?

[typescript-bot]

This issue has been marked as "Design Limitation" and has seen no recent activity. It has been automatically closed for house-keeping purposes.