NonNullable doesn't work on mapped types instantiated with null/undefined

[Andarist]

🔎 Search Terms

mapped nonnullable empty object null undefined instantiation

🕗 Version & Regression Information

• This changed in PR: Improve intersection reduction and CFA for truthy, equality, and typeof checks #49119

⏯ Playground Link

https://www.staging-typescript.org/play?ts=5.4.0-dev.20240124#code/C4TwDgpgBAYg9nAPAFQHxQLxQHJwHbYCuANsQIYBGxEiA3lANoDSUAlnlANYQhwBmUZAF0AXIOZCoAX1QBYAFALQkKACUIAZxLBMsBIjwliqIA

💻 Code

type Foo<T> = NonNullable<{ [K in keyof T]: T[K] }>

type Result = Foo<null>

🙁 Actual behavior

Result is of type null

🙂 Expected behavior

Result should be of type never

Additional information about the issue

This likely gets closed as a design limitation like the one here: #56644

[ahejlsberg]

This likely gets closed as a design limitation like the one here: #56644

That is indeed what I'm going to do. 😄

[typescript-bot]

This issue has been marked as "Design Limitation" and has seen no recent activity. It has been automatically closed for house-keeping purposes.