Repository navigation
control flow narrowing is broken in nightly build #10228
Description
nightly build August 9, 2016
the following used to work in July 30 build
interface A { kind: 'A'; }
interface B { kind: 'B'; }
type C = A | B | undefined;
function never(_: never): never {
throw new Error();
}
function useA(_: A): void {
}
function useB(_: B): void {
}
declare var c: C;
if (c === undefined) {
} else {
switch (c.kind) {
// below expected: narrowing to work, actual: doesn't work:
case 'A': useA(c); break;
case 'B': useB(c); break;
default: never(c);
}
}
Activity
zpdDG4gta8XKpMCd commentedon Aug 9, 2016
undefined,voidandnullif it mattersahejlsberg commentedon Aug 9, 2016
This is caused by the stricter discriminant property check introduced in #10188. It's an easy fix, we just need to ignore
undefined,null, andvoidin the declared type when checking whether a property in a particular declared type is a discriminant property. I will put up a fix later today.zpdDG4gta8XKpMCd commentedon Aug 11, 2016
works, thanks!