testAllBase64Features_librt fails with Python 3.14.4 #21120
Description
Bug Report
Yes, I know that Python 3.14.4 is not yet released, but the Python3.14 package in Debian's development distribution (sid a.k.a. unstable) is built from the "3.14 branch 2026-03-27."
which includes Do not ignore excess Base64 data after the first padded quad
and thus test
_________________________ testAllBase64Features_librt __________________________
[gw0] linux -- Python 3.14.3 /usr/bin/python3.14
data: /build/reproducible-path/package/mypyc/test-data/run-base64.test:1:
Failed: Invalid output (/build/reproducible-path/package/mypyc/test-data/run-base64.test, line 1)
----------------------------- Captured stdout call -----------------------------
*** Exit status: 1
----------------------------- Captured stderr call -----------------------------
Generated files: /build/reproducible-path/package/.mypyc_test_output (for first failure only)
Expected:
Actual:
<< test_decode_with_extra_data_after_padding >> (diff)
Traceback (most recent call last): (diff)
File "driver.py", line 57, in <module> (diff)
raise failures[-1][1][1] (diff)
File "driver.py", line 28, in <module> (diff)
test_func() (diff)
~~~~~~~~~^^ (diff)
File "run-base64.test", line 149, in test_decode_with_extra_data_after_padding (diff)
check_decode(b"eA==x", encoded=True) (diff)
File "run-base64.test", line 70, in check_decode (diff)
assert b64decode(enc) == getattr(base64, "b64decode")(enc) (diff)
File "/usr/lib/python3.14/base64.py", line 85, in b64decode (diff)
return binascii.a2b_base64(s, strict_mode=validate) (diff)
~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^ (diff)
binascii.Error: Incorrect padding (diff)
Update the test output using --update-data (implies -n0; you can additionally use the -k selector to update only specific tests)
------------------------------ Captured log call -------------------------------
INFO root:dist.py:1018 running build_ext
INFO root:build_ext.py:538 building 'native' extension
INFO root:dir_util.py:58 creating build/temp.linux-x86_64-cpython-314/build
INFO root:spawn.py:77 x86_64-linux-gnu-gcc -fno-strict-overflow -Wsign-compare -DNDEBUG -g -O2 -Wall -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -I/build/reproducible-path/package/.pybuild/cpython3_3.14_mypy/build/mypyc/lib-rt -I/usr/include/python3.14 -c build/__native.c -o build/temp.linux-x86_64-cpython-314/build/__native.o -O0 -g1 -Werror -Wno-unused-function -Wno-unused-label -Wno-unreachable-code -Wno-unused-variable -Wno-unused-command-line-argument -Wno-unknown-warning-option -Wno-unused-but-set-variable -Wno-ignored-optimization-argument -Wno-array-bounds -Wno-stringop-overread -Wno-stringop-overflow -Wno-cpp -UNDEBUG
INFO root:dir_util.py:58 creating build/lib.linux-x86_64-cpython-314
INFO root:spawn.py:77 x86_64-linux-gnu-gcc -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-z,relro -g -fwrapv -O2 -Wl,-z,relro -Wl,-z,now -Wdate-time -D_FORTIFY_SOURCE=2 build/temp.linux-x86_64-cpython-314/build/__native.o -L/usr/lib/x86_64-linux-gnu -o build/lib.linux-x86_64-cpython-314/native.cpython-314-x86_64-linux-gnu.so
INFO root:file_util.py:130 copying build/lib.linux-x86_64-cpython-314/native.cpython-314-x86_64-linux-gnu.so ->
Is this important, or can we freely ignore this test and publish mypy 1.20.0 to Debian? Or should we wait until a fix is agreed upon?