[mypyc] Fix b64decode to match new cpython behavior#21200
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p-sawicki merged 1 commit intopython:masterfrom Apr 10, 2026
Merged
[mypyc] Fix b64decode to match new cpython behavior#21200p-sawicki merged 1 commit intopython:masterfrom
p-sawicki merged 1 commit intopython:masterfrom
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JukkaL
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Apr 10, 2026
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Fixes #21120
Behavior of
base64.b64decodewas recently fixed in cpython to no longer stop processing the input data after the first padded quad. This resulted in a failure in one of our tests as the result of the librt implementation was no longer the same.Update the librt implementation to match the new correct behavior. Inputs where there are valid base64 characters after padding are rejected by
libbase64so we fall back to the slow path where we preprocess the input. Currently this preprocessing matches the buggy behavior where we stop processing after the first padded quad. Change this to instead ignore padding in the middle of input, and only copy padding at the end.Behavior of librt will now be correct regardless of python version at runtime as it doesn't seem worthwhile to preserve the buggy behavior for compatibility. So modify the test to only perform checks on input where there's data after padding with the python versions that have the bugfix.