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non-resolvable conditional type assignment causes error #42321

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Description

Bug Report

When in a generic function a conditional type cannot be resolved and is remained as is, nothing can be assigned to it (apparently).

🔎 Search Terms

conditional type assignment

🕗 Version & Regression Information

  • I tested this on version 4.1.2 and nightly. Playground's toolbar was not functioning, so I couldn't check other versions.

⏯ Playground Link

Playground's toolbar was not functioning, so I couldn't check other versions. I reloaded the page a few times and waited for some time, and used different browsers, but it didn't work.

💻 Code

function f<T>() {
    const a: T = null!;
    const b: T extends string ? T : T = a;
}

🙁 Actual behavior

Gives this error: Type 'T' is not assignable to type 'T extends string ? T : T'. (2322)

🙂 Expected behavior

It should check the type of a against the two conditional cases and type-check successfully.

Activity

  1. RyanCavanaugh commented on Jan 13, 2021

    @RyanCavanaugh
    Member

    See #30639

  2. typescript-bot commented on Jan 16, 2021

    @typescript-bot
    Contributor

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

  3. locked as resolved and limited conversation to collaborators on Oct 21, 2025
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