`zlib.Decompress.flush()` silently returns corrupted output instead of raising `zlib.error`

[StanFromIreland]

Bug report

Bug description:

zlib.Decompress.flush() discards errors returned by inflate(), so corrupt data comes back truncated and garbled with no exception, while decompress() reports this correctly.

>>> import zlib
>>> data = zlib.compress(b'abcdefgh' * 200, 9)
>>> corrupt = data[:15] + bytes(60)  # Corrupt the valid stream
>>> d = zlib.decompressobj()
>>> d.decompress(corrupt)  # decompress errors correctly
Traceback (most recent call last):
  File "<python-input-4>", line 1, in <module>
    d.decompress(corrupt)
    ~~~~~~~~~~~~^^^^^^^^^
zlib.error: Error -3 while decompressing data: incorrect data check
>>> d = zlib.decompressobj()
>>> d.decompress(corrupt, 1)  # leaving rest uncomsumed
b'a'
>>> d.flush()  # no flush, corrupted output
b'bcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdeP'

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-156173: Fix zlib.Decompress.flush() silently returning corrupted output instead of raising zlib.error #156176