Bugfix: Don't mutate fragments that are attached to query documents

[nevir]

This fixes an issue that arises when you perform the same query multiple times, and that query has fragments.

Because addFragmentsToDocument appends fragments to queryDoc.definitions, each time the query is performed, the query document gains a new copy of each fragment. This is particularly egregious, since graphql-tag maintains an identity map for queries.

For example, the following currently results in a server error (duplicate fragment authorDetails) on the second query:

const fragments = createFragment(gql`
  fragment authorDetails on Author {
    author {
      firstName
      lastName
    }
}`);
const query = gql`{ author { ...authorDetails } }`;

client.query({query, fragments}); // Success
client.query({query, fragments}); // BOOM: Duplicate fragment authorDetails

[Poincare]

I assume the cloneShallow works (as opposed to a deep clone) since we have OperationDefinitions as a top level attribute of the Document?

[nevir]

Yeah; definitions is the only value being mutated here

[stubailo]

Can we add a comment about this? That we are basically using this to clone the definitions array?

Could we achieve this in a simpler way using:

queryDoc = {
  definitions: [...queryDoc.definitions],
};

[nevir]

There's a few more properties on a Document than just the definitions - I'll go w/ assign (since we can't object spread in TypeScript)

[Poincare]

Looks good to me other than the question I commented. Once this is rebased and @stubailo can review, we can probably merge.

[nevir]

rebased

[stubailo]

We either need to add a comment about the clone, or replace it with a more explicit clone of definitions specifically, then we can merge!

[nevir]

updated to use assign instead of clone

[stubailo]

Thanks!