Type aliases differ from interfaces in that they aren't guaranteed to keep their name as they are used throughout the compiler. In part, this is a trade-off on what gives them their flexibility, but the downside is that sometimes TypeScript shows an object instead of the name. In 4.2, the compiler keeps track of the original name for a type alias in more places. Reducing the size of error messages and hover hints.

type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "square"; size: number }
  | { kind: "rectangle"; width: number; height: number };

type Named = { name: string };

// Previously: Shape
declare let shape: Shape;

declare let optionalShape: Shape | undefined;

// Previously: { kind: "circle"; radius: number; | { kind: "square"; size: number; | { kind: "rectangle"; width: number; height: number; | undefined
declare let namedShape: Shape & Named;

// Previously: ({ kind: "circle"; radius: number; Named) | ({ kind: "square"; size: number; Named) | ({ kind: "rectangle"; width: number; height: number; Named) | undefined
declare let optionalNamedShape: (Shape & Named) | undefined; // (Shape & Named) | undefined