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Conditional type unexpectedly non-distributive with never #57343
Description
🔎 Search Terms
never, intersection, contradiction
🕗 Version & Regression Information
- This changed in commit or PR Reduce intersections by discriminants #36696
⏯ Playground Link
💻 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.
Activity
[-]Conditional with nover [/-][+]Conditional type unexpectedly non-distributive with `never`[/+]fatcerberus commentedon Feb 8, 2024
Possibly related to/same root cause as #57210?
edit: oh, you already said it was a do-over of 57210 in the OP, nevermind