fix(gateway): Correctly handle unions with nested conditions that have no possibleTypes
#4071
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abernix
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May 8, 2020
abernix
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Sep 4, 2020
…e no `possibleTypes` (apollographql/apollo-server#4071) Skip collectFields for INLINE_FRAGMENTs and FRAGMENT_SPREADs when they have no possibleTypes. A field with no possibleTypes can be dropped / ignored from the query since the requested field exists within an impossible condition. Thus, we can skip the collectFields step altogether for fields which have no possibleTypes. The effect of skipping this step is that invalid fields are no longer represented within the splitFields function, thereby resolving the issue. Apollo-Orig-Commit-AS: apollographql/apollo-server@e0858d8
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Problem
The nested
forloops withinsplitFieldsthat utilizegroupByResponseNameandgroupByParentTypemake a false assumption that the incoming fields are all valid. In this case, an "invalid" field is one with nopossibleTypes.In its current state, the
splitFieldsfunction can consume an invalid field, leaving other valid, similarly-grouped fields ignored (only one will be taken). If an invalid field is consumed, the others will be ignored and the invalid field will subsequently be dropped, meaning the valid field is never represented due to the existence of an invalid field.Solution
A field with no
possibleTypescan be dropped / ignored from the query since the requested field exists within an impossible condition. Thus, we can skip thecollectFieldsstep altogether for fields which have nopossibleTypes. The effect of skipping this step is that invalid fields are no longer represented within thesplitFieldsfunction, thereby resolving the issue.Fixes #3983