Mapped types with direct and aliased keyof usage

[arusakov]

TypeScript Version: master (fc1f6e3)

Code

type X = {
  a?: any;
  b: any;
}

type Keys = keyof X;

type Direct = {
  [K in keyof X]: any;
}
// type Direct = {
//   a?: any; - optional
//   b: any;
// }

type WithAlias = {
  [K in Keys]: any;
}
// type WithAlias = {
//   a: any; - required
//   b: any;
// }

Expected behavior:
Types Direct and WithAlias have the same a property. I think that a property must be required in both Direct and WithAlias types.

Actual behavior:
Types Direct and WithAlias have different a property (optional and required).

[ahejlsberg]

This is working as intended. See #12563.