Interface unions type checking

[jspri]

TypeScript Version: 2.4.0

Code

interface Foo {
  a: string;
}

interface Bar extends Foo {
  b: string;
  c: string;
}

// d is neither foo nor bar!
const d: Foo | Bar = {
  a: 'lol',
  b: 'kek',
};

Expected behavior:

You would expect the code above to throw an error as d can not be resolved to type foo or type bar.

Actual behavior:

Code compiles without error.

[jcalz]

duplicate of #14383?

[jspri]

Yeah, thanks.