Union discriminated on object

[velvet charm]

Hi all, hopefully a quick one - does anyone know why using an object as a discriminated value does not cause the related types to narrow?

[versed depot]

m.a.t.t.t#0

Playground Link

Preview:```ts
type Union =
| {disc: "a"; value: number}
| {disc: "b"; value: string}

function abc(u: Union) {
switch (u.disc) {
case "a": {
u.value
// ^?
}
}
}

type UnionObj =
| {disc: {i: "a"}; value: number}
| {disc: {i: "b"}; value: string}
...```

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[olive turtle]

Discriminated unions are a special case and that special case wasn't extended to nested properties

https://github.com/microsoft/TypeScript/issues/18758