filtering lists of union types

[hartig]

Consider the following part of a DB schema.

union U = A | B

type X {
  myUs: [U]
}

When generating the API schema for this part, the field myUs is extended with an argument that allows users to filter the retrieved list of U objects. However, since U is a union type, it is not immediately clear what the corresponding input type for this filter should look like. The purpose of this issue is to develop an idea for this case.