fix(federation): fix left-behind selections in fragment reuse #6093
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Sometimes, fragment reuse would leave behind a selection in a selection
set that is also part of a fragment that was applied to that selection
set. That's suboptimal.
An example from the Apollo codebase is an output like this:
Here
errors.locations.*
is selected twice.The cause is this difference in our
intersection
implementation:https://github.com/apollographql/federation/blob/df5eb3cb0e2b4802fcd425ab9c23714de2707db3/internals-js/src/operations.ts#L2676-L2680
If a field selection's subselection completely disappears in
intersection()
, we previously kept the field selection, instead ofremoving it entirely.
By returning
None
we will now correctly remove the duplicateerrors
selection.Checklist
Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.
Exceptions
I did not add a unit test for this as we do not expect to rely on
fragment reuse long-term. Existing tests pass and I manually
tested the problematic Apollo queries.
Footnotes
It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this. ↩
Configuration is an important part of many changes. Where applicable please try to document configuration examples. ↩
Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions. ↩