Conditional type unexpectedly non-distributive with `never`

[rotu]

🔎 Search Terms

never, intersection, contradiction

🕗 Version & Regression Information

• This changed in commit or PR Reduce intersections by discriminants #36696

⏯ Playground Link

Workbench Repro

💻 Code

type IsNumber<T> = T extends number ? true : false

type Conflicted = {x:true} & {x:false} // never
//   ^?

type Ex1 = IsNumber<Conflicted> // true. Should be never 
//   ^?
type Ex2 = IsNumber<never>
//   ^?

// Conflicted starts behaving like `never` again when distributivity is forced by putting it in a union
type Ex3 = IsNumber<"OEEE" | Conflicted> // false (boolean in TypeScript 4.6.4)
//   ^?
type Ex4 = IsNumber<1 | Conflicted> // true
//   ^?

🙁 Actual behavior

Ex1 is true.

🙂 Expected behavior

IsNumber<Conflicted> should be never. This is a distributive conditional.

Additional information about the issue

This also manifests as ReturnType<T> being unknown when T is a conflicted intersection.

Originally submitted in #57210 which was overly broad.

[fatcerberus]

Possibly related to/same root cause as #57210?
edit: oh, you already said it was a do-over of 57210 in the OP, nevermind