Error on types when using multiple conditional properties

[Arkellys]

🔎 Search Terms

"jsdoc conditional properties", "typescript conditonnal properties", "type conditon"

🕗 Version & Regression Information

This is the behavior in every version I tried, and I reviewed the FAQ for entries about conditional types

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.4.5#code/FASwdgLgpgTgZgQwMZQAQGED2YAmIIjboBqCANgGLkDOaA3sKk6kgPwBcqiZtwAvsFCRYiFBmx4CRUmQAqMAK71GzJJwiKo-QeGjxkaLLnyEwAIRlUey5qgBGHLjS0Che0YYknsF8vKWoDLZ26prabiIGqGYItIEqTAic1BrgAOb8ANyCSNgpqND5ALyoABS5YHAgaZwxcQBkZUaSpr5ymqgAPuLGUuaWzgCUqI2lzd5gJH4d3eN9U5RDw0UAfE7WwBX5MFAQCjDmmJhkqCWlAG7knHZHZFAIYMPXt-dgp2uol2TZwIUQpXRUElUAAiBAggA09k4Oz2BzMt1KGiUwz4gyAA

💻 Code

interface ConditionCValFalse {
    c?: false
}

interface ConditionCValTrue {
    c: true
}

interface ConditionBValFalse {
    b?: false
}

interface ConditionBValTrue {
    b: true
}

interface Base {
    a: string
};

const test = (config: Base & (ConditionBValTrue | ConditionBValFalse) & (ConditionCValTrue | ConditionCValFalse )) => false
const returnBool = (val: boolean) : boolean =>  val;

test({ a: "a", b: returnBool(true) }) // Type 'boolean' is not assignable to type 'true'

🙁 Actual behavior

When using a second set of conditional properties, the first one throws a type error while it passes when using the condition alone.

Argument of type '{ a: string; b: boolean; }' is not assignable to parameter of type 'Base & (ConditionBValFalse | ConditionBValTrue) & (ConditionCValFalse | ConditionCValTrue)'.
  Type '{ a: string; b: boolean; }' is not assignable to type 'Base & ConditionBValTrue & ConditionCValTrue'.
    Type '{ a: string; b: boolean; }' is not assignable to type 'ConditionBValTrue'.
      Types of property 'b' are incompatible.
        Type 'boolean' is not assignable to type 'true'.(2345)

If I remove the second condition, or that I passes true or false directly, I get not error:

const test = (config: Base & (ConditionBValTrue | ConditionBValFalse)) => false
const returnBool = (val: boolean) : boolean =>  val;

test({ a: "a", b: returnBool(true) })

const test = (config: Base & (ConditionBValTrue | ConditionBValFalse) & (ConditionCValTrue | ConditionCValFalse)) => false
const returnBool = (val: boolean) : boolean =>  val;

test({ a: "a", b: true })

Somehow, when passing the c property – which is not supposed to be required – it passes:

const test = (config: Base & (ConditionBValTrue | ConditionBValFalse) & (ConditionCValTrue | ConditionCValFalse)) => false
const returnBool = (val: boolean) : boolean =>  val;

test({ a: "a", b: returnBool(true), c: true })

It also passes if I only declare the a required property:

test({ a: "a" })

So b and c are indeed optional.

🙂 Expected behavior

I expect the type checking to be the same whether I passes one or multiple conditional properties. I believe all of these should work:

// Pass
test({ a: "a" })
test({ a: "a", b: true })
test({ a: "a", c: false })
test({ a: "a", b: returnBool(true), c: returnBool(false) })
test({ a: "a", b: returnBool(true), c: false })
test({ a: "a", b: true, c: returnBool(false) })

// Currently fail
test({ a: "a", c: returnBool(true) })
test({ a: "a", b: returnBool(true) })

Additional information about the issue

For the context, I'm trying to make some properties required based on other property values.

I realize that maybe there is better way to do this in TS, but actually my problem is in JSDoc, and I believe I'm more limited on what I can do with JSDoc synthax.

/**
 * @typedef {object} ConditionCValFalse
 * @property {false} [c]
 */

/**
 * @typedef {object} ConditionCValTrue
 * @property {true} c
 */

/**
 * @typedef {object} ConditionBValFalse
 * @property {false} [b]
 */

/**
 * @typedef {object} ConditionBValTrue 
 * @property {true} b
 */

/**
 * @typedef {object} Base
 * @property {string} a
 */

/**
 * @param {Base & (ConditionBValTrue | ConditionBValFalse) & (ConditionCValTrue | ConditionCValFalse)} config
 */
const test = (config) => false;

/**
 * @param {boolean} val
 * @returns {boolean}
 */
const returnBool = (val) =>  val;

test({ a: "a", b: returnBool(true) }); // Type 'boolean' is not assignable to type 'true'

My real code is on a React component, and unlike the example above, even passing all the optional properties throws the error.

[Joe Calzaretta]

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.

[Ryan Cavanaugh]

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.