Allow field overrides when spreading types (not spreading values)

[nvie]

Example

type Thing = {|
  id: number,
  name: string,
|};

type Thing$External = {|
  ...Thing,
  id: string,  // Overwrite ID's to be strings, not numbers
|};

function toExternal(thing: Thing): Thing$External {
  return { ...thing, id: thing.id.toString() };
  //     ^ Cannot return object literal because number [1] is incompatible
  //       with string [2] in property `id`.
}

Expected behaviour

This should work.

Try link

[villesau]

Here is a pr that should fix the issue: #7298

[nmote]

This no longer errors on master