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gh-132835: Add defensive NULL checks in mro resolution#134763
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Currently, there are a few places where tp_mro could theoreticallybecome NULL, but do not in practice. We should defensively check forNULL values to ensure that any changes do not introduce a crash and thatstate invariants are upheld.
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picnixz approved these changesMay 27, 2025
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Currently, there are a few places where
type->tp_mrocould theoretically be NULL, but are not in practice. We should defensively assert these NULL values don't occur to ensure that any changes do not introduce a crash and that state invariants are upheld.The assertions added in this PR are all instances where a NULL value would get passed to something not expected a NULL, so it is better to catch an assertion failure than crash later on.
There are a few cases where it is OK for the return of
lookup_tp_mroto be NULL, such as when passed tois_subtype_with_mro, which handles this explicitly.