scalar ThisIsAScalar @specifiedBy(url: "https://example.com")

type WithFieldA { a: String }
type WithFieldB { b: String }

# Extension can't add a non-object type
union NonObjectType = WithFieldA | WithFieldB
extend union NonObjectType = ThisIsAScalar

# Extension can't add duplicate members
union DuplicateMembers = WithFieldA
extend union DuplicateMembers = WithFieldA | WithFieldB

# Extension can't add duplicate directives
directive @nonRepeatable on UNION
union DuplicateDirective @nonRepeatable = WithFieldA
extend union DuplicateDirective @nonRepeatable = WithFieldB

type Query {
  x: Int
}