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Key for rest Tuple argument missing when mapping tuple type #57770

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trevorade opened this issue Mar 13, 2024 Β· 2 comments
Closed

Key for rest Tuple argument missing when mapping tuple type #57770

trevorade opened this issue Mar 13, 2024 Β· 2 comments
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Not a Defect This behavior is one of several equally-correct options

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@trevorade
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πŸ”Ž Search Terms

"tuple", "tuple type"

πŸ•— Version & Regression Information

  • This changed between versions 5.3.3 and 5.4.2

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.4.2#code/C4TwDgpgBA4hwBUCuYA2EDSEQGcA8ya0EAHsBAHYAmOUSFA1hQPYDuFA2gLoB8UAvFADeHDFACWFKA2zMAZlELouALigYAvhxkh5ilMoDcAKGMB6M1ACSUgKwA6ACz2ATFFbQA5vCgADCkgAtgBGEABOUAA+UABEAAwxvuaWNlAOAMz26e5ePv5BoRHR8TFRsQCMicZCoJBQ5DjAArDwSpjY+ByNYZKeADRQ9kMBIeHcvBrJUNNQAHoA-KYW1nZOrjlQ3k2+JWVuxZW+UAAUrAAW4gDGZxK0EACOSOIAbgCG6BRNrxQgrK+4AEopqkMlkNls-LsDqVoi4kjVwNAGk1BHBEAZ2rg8F1gD0KP0oCNChMpjMFsYgA

πŸ’» Code

type GetTupleKeys<Tuple extends unknown[]> = {[K in keyof Tuple]: K}[keyof Tuple];

// In 5.4.2 we get `number | "0"`
// In 5.3.3 we get `number | "0" | "1"`
{type test = GetTupleKeys<[string, ...number[]]>}
//    ^?

// In 5.4.2 we get `"0" | 2 | "1"` (which is equivalent anyways)
// In 5.3.3 we get `"0" | "1" | 2`
{type test = GetTupleKeys<[string, number]>}
//    ^?

πŸ™ Actual behavior

In 5.4.2, rest arguments in tuples no longer get a dedicated key/index when mapping the tuple type. In the above example, the tuple type [string, ...number[]] effectively produces the keys number | "0"

πŸ™‚ Expected behavior

No regression. The above example should be as 5.3.3 and resolve to the keys number | "0" | "1"

Additional information about the issue

This is specifically impacting the following code:
https://github.com/sindresorhus/type-fest/blob/main/source/set-parameter-type.d.ts#L7

As reported in:
sindresorhus/type-fest#831

@Andarist
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It works as intended as per the change in #57031

@RyanCavanaugh RyanCavanaugh added the Not a Defect This behavior is one of several equally-correct options label Mar 15, 2024
@typescript-bot
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This issue has been marked as "Not a Defect" and has seen no recent activity. It has been automatically closed for house-keeping purposes.

@typescript-bot typescript-bot closed this as not planned Won't fix, can't repro, duplicate, stale Mar 18, 2024
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