`require-selections` does not report issues on `FragmentSpread`s within `GraphQLUnionType`

[maciesielka]

Issue workflow progress

Progress of the issue based on the Contributor Workflow

• [x] 1. The issue provides a reproduction available on GitHub, Stackblitz or CodeSandbox
• [x] 2. A failing test has been provided
• [x] 3. A local solution has been provided
• [x] 4. A pull request is pending review

---

Describe the bug

require-selections handles only InlineFragment spreads with GraphQLUnionTypes, despite named FragmentSpreads being valid GraphQL that should receive the same treatment.

https://github.com/dimaMachina/graphql-eslint/blob/58467e65f0283f5ad7a7ca8a3f0301b7669b4416/packages/plugin/src/rules/require-selections.ts#L172-L182

To Reproduce

Steps to reproduce the behavior:

The failing test in the linked PR provides the best example for the bug (see commit that adds that test), but a simplified schema is reproduced below:

type User {
  id: ID
  name: String
  posts: [Post]
}

type Post {
  id: ID
  title: String
  author: [User!]!
}

type Query {
  user: User
  userOrPost: UserOrPost
}

union UserOrPost = User | Post

fragment UnionFragment on UserOrPost {
  ...UserFields
}

fragment UserFields on User {
  name
}

query {
  userOrPost {
    # no error is reported here, even though `...UnionFragment` does not select `id`
    ...UnionFragment
  }
}

Expected behavior

An error should be reported for FragmentSpread just like it is for InlineFragments within GraphQLUnionTypes.

Environment:

• @graphql-eslint/eslint-plugin: 4.0.0