Discriminated unions and object literals

[thorn0]

I'm not sure if it's a bug.

TypeScript Version: 2.4.0 / nightly (2.5.0-dev.201xxxxx)

playground, 2.5.1-insiders.20170825

Code

interface Square {
    kind: "square";
    size: number;
}

interface Rectangle {
    kind: "rectangle";
    width: number;
    height: number;
}
type Shape = Square | Rectangle;

var a: Square = { kind: 'square', size: 100, width: 50 }; // error
var b: Shape = { kind: 'square', size: 100, width: 50 };  // oops

Expected behavior:

Same error. From the kind property, TypeScript should understand that the second object literal is of type Square and prevent us from attaching the width property to it.

Actual behavior:

no error

[mhegazy]

Duplicate of #12745

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.