fix: Fix readFragment() not deriving complex return types

[kitten]

Summary

When a complex fragment type (e.g. any fragment that derives to a union type of multiple object shapes) is passed to readFragment() then the return type would only infer as the first type of the union.

// derives to `{ wallOfText: string } | { maxLength: number }`
const fragment = graphql(`
  fragment Fields on ITodo {
    ... on BigTodo {
      wallOfText
    }
    ... on SmallTodo {
      maxLength
    }
  }
`);

// previously derived to: `{ wallOfText: string }`
// rather than: `{ wallOfText: string } | { maxLength: number }`
const fields = readFragment(fragment, data);

Set of changes

• Add tests for readFragment inputs
• Remove Data generic on readFragment and instead infer Data from Document directly

[changeset-bot]

🦋 Changeset detected

Latest commit: dccaf72

The changes in this PR will be included in the next version bump.

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[JoviDeCroock]

What a find