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Fields have an invisible "never make it undefined" state #60411

Closed as not planned
#64100
Closed as not planned
Fields have an invisible "never make it undefined" state#60411
#64100
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DuplicateAn existing issue was already created

Description

@verytactical
verytactical
opened on Nov 4, 2024

🔎 Search Terms

undefined forever

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/C4TwDgpgBAqgdgZwseATCAzAlnCqAqA9gPIBGANlgG5aFwA8+AfFALxQDeUA2gApQ4oAawghCGKPgC6AWgD8ALkl8pUAD5QArnHTZcqANxQAvlABQoSFADKyNJhx5GLdlz4C4w0eMlSl+FXUtHQd9E3NLaHwACwgAdWiAQ2A2GzsQvSd4JBQMxwISCmpaBi5ExSgARhMmJjMgA

💻 Code

type UnsetUndefinedToOblivion<T> = { [P in keyof T]-?: T[P] | undefined; } 
type SetUndefined<T> = { [P in keyof T]: T[P] | undefined } 
type TheWhat = SetUndefined<UnsetUndefinedToOblivion<{ a?: 1 }>>

🙁 Actual behavior

type TheWhat = {
    a: 1;
}

🙂 Expected behavior

type TheWhat = {
    a: 1 | undefined;
}

Additional information about the issue

Temporary fix:

type UnsetTheUnset<T> = { [P in keyof T & {}]: T[P] }
type TheWhat = SetUndefined<UnsetTheUnset<UnsetUndefinedToOblivion<{ a?: 1 }>>>

Activity

  1. jcalz commented on Nov 4, 2024

    @jcalz
    Joe Calzaretta (jcalz)
    on Nov 4, 2024 · Hidden as outdated

  2. verytactical commented on Nov 4, 2024

    @verytactical
    verytactical
    on Nov 4, 2024
    Author

    Joe Calzaretta (@jcalz) This is a different issue. Here it's not only removed, it's impossible to even set it afterwards.

  3. jcalz commented on Nov 4, 2024

    @jcalz
    Joe Calzaretta (jcalz)
    on Nov 4, 2024 · Hidden as outdated

  4. verytactical commented on Nov 4, 2024

    @verytactical
    verytactical
    on Nov 4, 2024
    Author

    removing undefined is happening at the end of the type manipulation

    Honestly I would never expect that. Thanks for explaining!

    It's probably still related to #31025

    It's definitely related, because if undefined was never removed along with optionality, it wouldn't be removed at incorrect time :)

  5. jcalz commented on Nov 4, 2024

    @jcalz
    Joe Calzaretta (jcalz)
    on Nov 4, 2024 · Hidden as outdated

  6. Andarist commented on Nov 4, 2024

    @Andarist
    Mateusz Burzyński (Andarist)
    on Nov 4, 2024
    Contributor

    I believe this is just a display issue as this works alright:

    type UnsetUndefinedToOblivion<T> = { [P in keyof T]-?: T[P] | undefined };
type SetUndefined<T> = { [P in keyof T]: T[P] | undefined };
type TheWhat = SetUndefined<UnsetUndefinedToOblivion<{ a?: 1 }>>;

const theWhat: TheWhat = {
  a: undefined, // ok
};

    It's likely a duplicate of #59948 and likely is being fixed by #59957 // EDIT: yep, I just pushed a test case there based on this issue

  7. jcalz commented on Nov 4, 2024

    @jcalz
    Joe Calzaretta (jcalz)
    on Nov 4, 2024
    Contributor

    Okay, okay this has nothing to do with #31025 then. Sorry! I'll hide my comments (including this one, soon) to cut down on noise.

  8. Ryan Cavanaugh (RyanCavanaugh)
    added
    DuplicateAn existing issue was already created
    on Nov 4, 2024

  9. typescript-bot commented on Nov 7, 2024

    @typescript-bot
    TypeScript Bot (typescript-bot)
    on Nov 7, 2024
    Contributor

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

  10. TypeScript Bot (typescript-bot)
    closed this as not plannedon Nov 7, 2024
  11. microsoft
    locked as resolved and limited conversation to collaborators on Oct 22, 2025
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