Discriminated union narrowing fails when use template literal types as tag

TypeScript Version: 4.2.0-dev.20201211

Search Terms: narrowing, discriminated union, template literal types

Code

type Types<T extends string> = {
  one: `${T}/one`;
  two: `${T}/two`;
}
type OneObj<T extends string> = {
  type: Types<T>["one"];
  one: string;
}
type TwoObj<T extends string> = {
  type: Types<T>["two"];
  two: string;
}
type OneOrTwoObj<T extends string> = OneObj<T> | TwoObj<T>

declare function acceptsOneObj<T extends string>(oneObj: OneObj<T>): void;
declare function acceptsTwoObj<T extends string>(twoObj: TwoObj<T>): void;

function f<T extends string>(oneOrTwoObj: OneOrTwoObj<T>, types: Types<T>){
  switch(oneOrTwoObj.type){
    case types.one:
     return acceptsOneObj(oneOrTwoObj); // Error: Argument of type 'OneOrTwoObj<T>' is not assignable to parameter of type 'OneObj<T>'.
    case types.two:
     return acceptsTwoObj(oneOrTwoObj); // Error: Argument of type 'OneOrTwoObj<T>' is not assignable to parameter of type 'OneObj<T>'.
  }
}

Expected behavior:
oneOrTwoObj should be narrowed to OneObj or TwoObj in function f

Actual behavior:
narrowing fails

Playground Link:
playground

Related Issues:

Commencez par la reproduction liée dans TypeScript Playground et la fonction générique f, en vous concentrant sur la manière dont le switch sur oneOrTwoObj.type gère les types de littéraux de modèle. Confirmez le comportement actuel, puis retracez le chemin de vérification des types pour le narrowing des unions discriminées. C’est terminé lorsque chaque branche du switch restreint oneOrTwoObj au OneObj ou TwoObj correspondant, de sorte que les appels à acceptsOneObj et acceptsTwoObj passent la vérification des types.