Removing 'optional' attributes from a type's properties disallow adding undefined as it's type

[KuSh]

Bug Report

🔎 Search Terms

type generic remove optional attribute

🕗 Version & Regression Information

I did test this on 4.4.4 and 4.5.0-beta using playground

⏯ Playground Link

Playground link with relevant code

💻 Code

type NullableType<T> = {
    [K in keyof T]-?: undefined extends T[K]
    ? T[K] | null | undefined
    : T[K]
}

🙁 Actual behavior

Removing optional attribute from type also remove undefined from final type
(when not removing optional attribute, final type is x?: typeof x | null | undefined)

🙂 Expected behavior

Removing optional attribute just removes the optional attribute and doesn't modify final type

[MartinJohns]

Sounds like a duplicate of #31025.

[RyanCavanaugh]

I don't see any repro here that demonstrates what you're talking about. Please provide an minimal/actionable sample that clearly demonstrates what you consider to be the bug

[KuSh]

Hi @RyanCavanaugh,

Hover over BadNullableTest in the playground, you'll see that previously optional attributes are defined as string | null instead of string | null | undefined

Regards,
Nicolas

[RyanCavanaugh]

Please provide an minimal/actionable sample that clearly demonstrates what you consider to be the bug, not a textual description of where to look in a long sample

[tadhgmister]

@KuSh does the relatively new compiler option exactOptionalPropertyTypes make it behave the way you are expecting? playground

type NullableType<T> = {
    [K in keyof T]-?: undefined extends T[K]
    ? T[K] | null | undefined
    : T[K]
}

type Test = {
    req: string
    opt?: string
    canBeNull: string | undefined
}

type EQ = NullableType<Test>
//   ^?
const shouldPass: EQ = {req: "", opt: undefined, canBeNull: undefined}

[KuSh]

@KuSh does the relatively new compiler option exactOptionalPropertyTypes make it behave the way you are expecting?

It seems so. But is effectively too recent for my current project (which use TS 4.3) and also has other consequencies as we're used to set optional props as undefined (outside of NullableTypes). Thanks for tip I'll keep that in mind 👍

[github-actions]

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