Type guard fails to make an array of full objects assignable to an array of partial objects

[KSXGitHub]

🔎 Search Terms

array of full objects assignable to an array of partial objects.

🕗 Version & Regression Information

(not a regression)

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.6.2#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-EbjZBTWa+KgfL7XanGf7a7kmEEkcGQ6GwuqI5Gx1HizHYkC4-GYIkkqj1RqDSmJlEjELISM+mNWavIGS0yEI4BovYHCDCM2lIA

💻 Code

interface InnerObject {
    foo: number[]
    bar: string[]
}

interface OuterObject {
    innerObjects?: InnerObject[]
}

interface SubOuterObject {
    innerObjects: Array<Pick<InnerObject, 'foo'>>
}

function takeSubOuter(_subOuterObject: SubOuterObject): void {}

export function passDirectly(outerObject: OuterObject): void {
    if (outerObject.innerObjects) { // assert that innerObjects is not undefined
        takeSubOuter(outerObject) // error: Type 'InnerObject[] | undefined' is not assignable to type 'Pick<InnerObject, "foo">[]'
    }
}

export function recreateThenPass(outerObject: OuterObject): void {
    if (outerObject.innerObjects) { // assert that innerObjects is not undefined
        takeSubOuter({ innerObjects: outerObject.innerObjects }) // this passes
    }
}

🙁 Actual behavior

In passDirectly, theif type guard fails to make outerObject compatible with SubOuterObject, even though it should have proven that outerObject.innerObjects is not undefined.

🙂 Expected behavior

There should be no compiler errors.

Additional information about the issue

No response

[MartinJohns]

Duplicate of #42384.

[typescript-bot]

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