disjoint unions regression between 0.19 and 0.21

[sakari]

the following program passes on flow 0.19 and in http://tryflow.org/#57c61a492a07f6e77eeb451064a5e2e4

function create(a: any): { type: 'B', data: number } | { type: 'A', data: string }
 {
  return {
    type: 'A',
    data: a
  }
}

but fails on OSX El Capitan with flow 0.21

test$ flow version
Flow, a static type checker for JavaScript, version 0.21.0
test$ flow
test.js:4
  4:   return {
              ^ object literal. This type is incompatible with
  2: function create(a: any): { type: 'B', data: number } | { type: 'A', data: string }
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ union: object type(s)


Found 1 error

[sakari]

interestingly if i set type: 'B' in the object literal flow does not complain

[jeffmo]

This is a known problem that we're actively working on. There are various nasty bugs with unions right now that we're ironing out.

Thanks for reporting!

[avikchaudhuri]

This will be fixed in an upcoming release.