gh-115398: Revert PyExpat_CAPI_MAGIC version bump by hartwork · Pull Request #116411 · python/cpython (original) (raw)
adorilson pushed a commit to adorilson/cpython that referenced this pull request
Revert "pythongh-115398: Increment PyExpat_CAPI_MAGIC for SetReparseDeferralEnabled addition (pythonGH-116301)"
This reverts part of commit eda2963. Why? this comment buried in an earlier code review explains:
I checked again how that value is used in practice, it's here:
Based on that code my understanding is that loading bigger structs from the future is considered okay unless PyExpat_CAPI_MAGIC differs, which implies that (1) magic needs to stay the same to support loading the future from the past and (2) that PyExpat_CAPI_MAGIC should only ever change for changes that do not increase size (but keep it constant).
To summarize, that supports your argument. I checked branches 3.8, 3.9, 3.10, 3.11, 3.12 now and they all have the same comparison code there so reverting that magic string bump will support seamless backporting.