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<key> is referenced directly or indirectly in its own type annotation #22018

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<key> is referenced directly or indirectly in its own type annotation#22018
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Design LimitationConstraints of the existing architecture prevent this from being fixed

Description

@KiaraGrouwstra
kiara (KiaraGrouwstra)
opened on Feb 17, 2018

TypeScript Version: 2.8.0-dev.20180217

Search Terms:

  • "is referenced directly or indirectly in its own type annotation"

Code

type Flatten<T> = {
  '1': Flatten<T extends Array<infer U> ? U : T>;
}[T extends number ? '1' : '1'];

(as mentioned in #21613)

Expected behavior: ok

Actual behavior:

error TS2502: ''1'' is referenced directly or indirectly in its own type annotation.

Playground Link: needs 2.8, playground is on 2.7

Related Issues: #6230

I saw similar issues on other types, though the greatest common denominator appeared to be recursion + conditional types (?).

Activity

  1. mhegazy commented on Mar 10, 2018

    @mhegazy
    Mohamed Hegazy (mhegazy)
    on Mar 10, 2018
    Contributor

    Type aliases are just that, aliases. the compiler will try to resolve the alias target once it sees it, if that causes it to loop over itself, then you will get the error. in this case a use of Flatten needs a constraint to be verified, and to do that the compiler will pull on the type, and will get into the cycle.

  2. Mohamed Hegazy (mhegazy)
    added
    Design LimitationConstraints of the existing architecture prevent this from being fixed
    on Mar 10, 2018

  3. typescript-bot commented on Mar 26, 2018

    @typescript-bot
    TypeScript Bot (typescript-bot)
    on Mar 26, 2018
    Contributor

    Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.

  4. TypeScript Bot (typescript-bot)
    closed this as completedon Mar 26, 2018
  5. microsoft
    locked and limited conversation to collaborators on Jul 25, 2018
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