Fix: Avoid infinite loop when merging siblings #282
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The logic for merging sibling fetch steps was missing a check to prevent cycles in the fetch graph, leading to infinite loops. This commit adds a check to ensure that two steps are not ancestors/descendants of each other before merging them.
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Summary of Changes
Hello @kamilkisiela, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request delivers a critical fix to the query planner by addressing an infinite loop bug that arose during the merging of sibling fetch steps. The core of the solution involves enhancing the merge logic to detect and prevent cyclical dependencies in the fetch graph, ensuring the stability and correctness of query plan generation. The changes are accompanied by a new, targeted test case to validate the fix.
Highlights
- Cycle Prevention: Implemented a new check within the
can_merge_withlogic for fetch steps. Merges are now prevented if the two steps are found to be ancestors or descendants of each other, thereby avoiding the creation of problematic cycles. - New Utility Function: Added a new public method,
is_ancestor_or_descendant, to theFetchGraphstruct. This function efficiently determines if a given pair of nodes in the graph has an ancestor-descendant relationship, which is crucial for the cycle prevention logic. - Test Coverage: Introduced a new test case,
issue_281_test, along with a dedicated supergraph fixture (281.supergraph.graphql). This test specifically targets the scenario that previously led to the infinite loop, ensuring the fix is effective and prevents future regressions.
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Code Review
This pull request effectively fixes a potential infinite loop during the sibling merge optimization in the query planner. The approach of checking for an ancestor-descendant relationship before merging is sound and directly addresses the root cause of the issue. The addition of a dedicated test case and GraphQL fixture ensures this scenario is covered against regressions. The changes are clear and well-implemented.
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The logic for merging sibling fetch steps was missing a check to prevent cycles in the fetch graph, leading to infinite loops. This commit adds a check to ensure that two steps are not ancestors/descendants of each other before merging them.
Closes #281