Microsoft/TypeScript
Voir sur GitHubConstraints of nested conditional types applied to constrained type variables are incorrect
Open
#59 868 ouverte le 5 sept. 2024
BugDomain: Conditional TypesHelp Wanted
Métriques du dépôt
- Stars
- (48 455 stars)
- Métriques de merge PR
- (Merge moyen 6j 17h) (9 PRs mergées en 30 j)
Description
🔎 Search Terms
constraints conditional types type variables nested
🕗 Version & Regression Information
- This is the behavior in every version I tried
⏯ Playground Link
💻 Code
type IsMatchingStringOneLevel<T extends string> = T extends `a${string}`
? true
: false;
function f2<S extends string>(x: IsMatchingStringOneLevel<S>) {
let t: true = x; // Error
let f: false = x; // Error
}
type IsMatchingStringTwoLevels<T extends string> = T extends `a${string}`
? T extends `${string}z`
? true
: false
: false;
function f3<S extends string>(x: IsMatchingStringTwoLevels<S>) {
let t: true = x; // Error
let f: false = x; // Ok but should be an error
}
🙁 Actual behavior
It doesn't error on the fourth assignment
🙂 Expected behavior
It should error
Additional information about the issue
This is just a variant of what was fixed for one-level conditionals in https://github.com/microsoft/TypeScript/pull/56004