Closed
Description
Bug Report
🔎 Search Terms
type guard conditional type
🕗 Version & Regression Information
- This changed between versions 4.2.3 and 4.3.2
⏯ Playground Link
Playground link with relevant code
💻 Code
interface A<S> {
a: S
}
interface B<S> {
b: S
}
interface C<S> {
c: S
}
type U1<S> = A<S> | B<S> | C<S>
function f1<S>(u: U1<S>): u is B<S> | C<S> {
return false
}
function test1<S>(x: U1<S>) {
if (!f1(x)) {
x.a //OK
}
}
type Cond<S> = S extends number ? B<S> : C<S>
type U2<S> = A<S> | Cond<S>
function f2<S>(u: U2<S>): u is Cond<S> {
return false
}
function test2<S>(x: U2<S>) {
if (!f2(x)) {
x.a //ERROR
}
}🙁 Actual behavior
The type guard is unable to narrow the type of x to A
🙂 Expected behavior
The type guard should narrow the type of x to A because it is not assignable to Cond<S>