`never` as keyof tuples/arrays behaves the same as `number`

🔎 Search Terms

tuple keyof never, tuple[never], array keyof never

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about this issue

Versions I tried:

• 5.2.2
• nightly (playground)

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.0-dev.20230923#code/C4TwDgpgBAglC8UDeBfA2gOwgNwgJwF0oB6YqQUHIotc8AoUSKAIQWSgEMAuKAZ2DwCWGAOZR01fEVIUqOfPXDQAwqzQFMcwiTKUJdBtAAiqvoJHq9UsoBlyXvyHCFjAKKtTDtRppWot9yKdoADFWAAp-UQAfKgBXAFsAI3wASk9LKG1fOzMo2MT8IA

💻 Code

type A = {}[never] // ✅ never
type B = { a: string }[never] // ✅ never
type C = [][never] // ✅ never
type D = [string][never] // ❌ string
type E = string[][never] // ❌ string
type F = (string | number)[][never]  // ❌ string | number

🙁 Actual behavior

After using a never key on tuples/arrays you get back the entirety of the tuple/array elements type.

🙂 Expected behavior

After using a never key on tuples/arrays you get back never, as when dealing with objects.

Additional information about the issue

Not sure if this has historical reasons to behave like it does, but couldn't find any specific info about it.

Start by reproducing the behavior in the linked TypeScript Playground, comparing the object, tuple, and array examples using never. Trace the compiler's indexed-access handling for tuple and array keys; done means those examples evaluate to never consistently with object indexing, with appropriate regression coverage.