https://github.com/facebook/flow/issues/1793

cmdline.txt

peterv@vilterp-mbp:flow-test$ flow version
Flow, a static type checker for JavaScript, version 0.25.0
peterv@vilterp-mbp:flow-test$ flow
flowTest.js:7
  7: var y: Foo = {...x, a: 5};
                  ^^^^^^^^^^^^ object literal. This type is incompatible with
  7: var y: Foo = {...x, a: 5};
            ^^^ union: object type(s)
  Member 1:
    3: type Foo = { type: 'foo', a: number, b: number } | { type: 'bar', c: string };
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ object type
  Error:
    3: type Foo = { type: 'foo', a: number, b: number } | { type: 'bar', c: string };
                                                                  ^^^^^ string literal `bar`. Expected string literal `foo`, got `bar` instead
    3: type Foo = { type: 'foo', a: number, b: number } | { type: 'bar', c: string };
                          ^^^^^ string literal `foo`
  Member 2:
    3: type Foo = { type: 'foo', a: number, b: number } | { type: 'bar', c: string };
                                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^ object type
  Error:
    3: type Foo = { type: 'foo', a: number, b: number } | { type: 'bar', c: string };
                          ^^^^^ string literal `foo`. Expected string literal `bar`, got `foo` instead
    3: type Foo = { type: 'foo', a: number, b: number } | { type: 'bar', c: string };
                                                                  ^^^^^ string literal `bar`


Found 1 error
peterv@vilterp-mbp:flow-test$ 

spreadUnionError.js

/* @flow */

type Foo = { type: 'foo', a: number, b: number } | { type: 'bar', c: string };

var x: Foo = { type: 'foo', a: 1, b: 2 };

var y: Foo = {...x, a: 5}; // this is a valid `Foo`, but Flow says it's not