[3.13] gh-132835: Add defensive NULL checks to MRO resolution (GH-134763) #140437
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…H-134763) Currently, there are a few places where tp_mro could theoretically become NULL, but do not in practice. This commit adds defensive checks for NULL values to ensure that any changes do not introduce a crash and that state invariants are upheld. The assertions added in this commit are all instances where a NULL value would get passed to something not expecting 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_mro to be NULL, such as when passed to is_subtype_with_mro, which handles this explicitly. (cherry picked from commit a8edca6) Co-authored-by: Emma Smith <[email protected]>
emmatyping
approved these changes
Oct 22, 2025
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Currently, there are a few places where tp_mro could theoretically
become NULL, but do not in practice. This commit adds defensive checks for
NULL values to ensure that any changes do not introduce a crash and that
state invariants are upheld.
The assertions added in this commit are all instances where a NULL value would get passed to something not expecting 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_mro to be NULL, such as when passed to is_subtype_with_mro, which handles this explicitly.
(cherry picked from commit a8edca6)
Co-authored-by: Emma Smith [email protected]