ts2556 is too restrictive when generics are involved

🔎 Search Terms

"generic", "tuple", "spread", "rest", "ts2556", "a spread argument must either have a tuple type or be passed to a rest parameter"

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about spreading into argument lists

⏯ Playground Link

https://www.typescriptlang.org/play?#code/CYUwxgNghgTiAEYD2A7AzgF3gMwFzwAoBKeAXgD54A3JAS2AFgAoZ0SWBZdLAD3zijBUEAJ7wA2gF1m2AgDoFPEgHpl8AO5IYAazTNmXTPAwgjpeAB4AKvBA8TKYGngChKURMnkCfeFZIUzPA48ooqakKm8ChIWJo6QA

💻 Code

declare const f: () => void

declare const x: readonly []
f(...x) // works

const test = <T extends readonly []>(x: T) =>
  f(...x) // does not work

🙁 Actual behavior

Attempting to spread a generically-typed value whose constraint guarantees tuple-ness into a compatible argument list is forbidden.

🙂 Expected behavior

I should be allowed to do this.

Additional information about the issue

Possibly-related issues:

• https://github.com/microsoft/TypeScript/issues/29919
• https://github.com/microsoft/TypeScript/issues/49802
• https://github.com/microsoft/TypeScript/issues/53541

Beginne damit, das generische Beispiel zur Tupelverteilung im verlinkten TypeScript Playground zu reproduzieren, und vergleiche es mit dem nicht-generischen Fall, der erfolgreich ist. Verfolge den Compilerpfad, der TS2556 für Verteilungen in Argumentlisten meldet, und füge Tests hinzu, die zeigen, dass der eingeschränkte generische Fall akzeptiert wird, während inkompatible Verteilungen weiterhin abgelehnt werden.