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Bug from #23592 - Type 'keyof U & K' does not satisfy the constraint 'string | number | symbol' #23648

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#23672
Closed
Bug from #23592 - Type 'keyof U & K' does not satisfy the constraint 'string | number | symbol'#23648
#23672
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ahejlsberg
Labels
BugA bug in TypeScriptFixedA PR has been merged for this issue
Milestone
TypeScript 2.9

Description

@kpdonn
Kevin Donnelly (kpdonn)
opened on Apr 24, 2018

TypeScript Version: 2.9.0-dev.20180424

Search Terms:
keyof, intersection, conditional types

Code

type Example<T, U> = { [K in keyof T]: K extends keyof U ? UnexpectedError<K> : NoErrorHere<K> }

type UnexpectedError<T extends PropertyKey> = T
type NoErrorHere<T extends PropertyKey> = T

Expected behavior:
No errors.

Actual behavior:
Error on K in UnexpectedError<K> with message

Type 'keyof U & K' does not satisfy the constraint 'string | number | symbol'.
  Type 'keyof U & K' is not assignable to type 'symbol'.

Playground Link:
Link (no error in playground)

Related Issues:
#23592

Activity

  1. ahejlsberg commented on Apr 24, 2018

    @ahejlsberg
    Anders Hejlsberg (ahejlsberg)
    on Apr 24, 2018
    Member

    The issue here is that we don't lift constraints over intersection types. Here's a simpler repro:

    function foo<T extends string | number, U extends string | number>(x: T & U) {
    let y: string | number = x;  // Error, but shouldn't be
}

    We need to lift the individual constraints of T and U such that the intersection type T & U appears to have the constraint string | number (formed by intersecting the individual constraints of T and U).

  2. ahejlsberg commented on Apr 24, 2018

    @ahejlsberg
    Anders Hejlsberg (ahejlsberg)
    on Apr 24, 2018
    Member

    The reason this shows up with #23592 is that we now have union type constraints for keyof T.

  3. Anders Hejlsberg (ahejlsberg)
    self-assigned this
    on Apr 24, 2018
  4. Anders Hejlsberg (ahejlsberg)
    added
    BugA bug in TypeScript
    on Apr 24, 2018
  5. Anders Hejlsberg (ahejlsberg)
    added this to the TypeScript 2.9 milestone on Apr 24, 2018

  6. ahejlsberg commented on Apr 24, 2018

    @ahejlsberg
    Anders Hejlsberg (ahejlsberg)
    on Apr 24, 2018
    Member

    Mohamed Hegazy (@mhegazy) Do you recall if we already have an issue for this?

  7. Anders Hejlsberg (ahejlsberg)
    added
    FixedA PR has been merged for this issue
    on Apr 24, 2018

  8. mhegazy commented on Apr 25, 2018

    @mhegazy
    Mohamed Hegazy (mhegazy)
    on Apr 25, 2018
    Contributor

    Mohamed Hegazy (@mhegazy) Do you recall if we already have an issue for this?

    do not think i have seen this one before.

  9. Anders Hejlsberg (ahejlsberg)
    closed this as completedin #23672on Apr 27, 2018
  10. microsoft
    locked and limited conversation to collaborators on Jul 31, 2018
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