Spread on object breaks assignability check

[wclr]

Didn't find an issue on this.

TypeScript Version: 2.2.2

Code

type A = {
  a: string,
  b: string
}

let a: A = {
  a: '1', b: '2', c: 3,
  ...{ x: 1 } // no error
} 

Expected behavior:
I would expect TS Error like in this case

type A = {
  a: string,
  b: string
}

let a: A = {
  a: '1', b: '2', c: 3 // error: Object literal may only specify known properties, and 'c' does not exist in type 'A'
} 

Actual behavior:
No error

[RyanCavanaugh]

See #12745

[wclr]

@RyanCavanaugh what spread has to do with unions?

[RyanCavanaugh]

Oops, #13878