Bug#1109030: python3-debian: Release.copy() fails trying to split multivalued fields that have already been split

[Emanuele Aina]

Package: python3-debian
Version: 1.0.1
Severity: normal
X-Debbugs-Cc: emanuele.aina at collabora.com

When trying to copy a `Release` object or any `_multivalued` subclass
the code calls the constructor via `self.__class__(self)` and then the
`_multivalued.__init__()` treats fields in ``_multivalued_fields` as
strings, even though they have already been parsed in the source object.

This leads to the following exception:

    Traceback (most recent call last):
      File "//home/em/deb822-test.py", line 18, in <module>
        r2 = r1.copy()
      File "/usr/lib/python3.13/site-packages/debian/deb822.py", line 602, in copy
        copy = self.__class__(self)
      File "/usr/lib/python3.13/site-packages/debian/deb822.py", line 1761, in __init__
        for line in filter(None, contents.splitlines()):   # type: str
                                 ^^^^^^^^^^^^^^^^^^^
    AttributeError: 'list' object has no attribute 'splitlines'

-- System Information:
Debian Release: trixie/sid
  APT prefers testing-security
  APT policy: (500, 'testing-security'), (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 6.15.4-200.fc42.x86_64 (SMP w/8 CPU threads; PREEMPT)
Kernel taint flags: TAINT_WARN
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: unable to detect

Versions of packages python3-debian depends on:
ii  python3                     3.13.3-1
ii  python3-charset-normalizer  3.4.2-1

python3-debian recommends no packages.

Versions of packages python3-debian suggests:
pn  gpgv         <none>
ii  python3-apt  3.0.0
pn  zstd         <none>

-- no debconf information
-------------- next part --------------
import debian
from debian.deb822 import Release

txt = """
Suite: testing
Codename: trixie
MD5Sum:
 70ddf531b5b7dbd059eb3fdb88566d4b  1963340 contrib/Contents-all
"""
r1 = Release(txt)
assert "md5sum" in Release._multivalued_fields
assert r1["MD5Sum"] == [
    {
        "md5sum": "70ddf531b5b7dbd059eb3fdb88566d4b",
        "size": "1963340",
        "name": "contrib/Contents-all",
    }
]
try:
    r2 = r1.copy()
except:
    print(f"BUG: {debian.__version__ = }")
    raise
# BUG: debian.__version__ = '0.1.51.dev2+g67bda81'
# Traceback (most recent call last):
#   File "//home/em/deb822-test.py", line 18, in <module>
#     r2 = r1.copy()
#   File "/usr/lib/python3.13/site-packages/debian/deb822.py", line 602, in copy
#     copy = self.__class__(self)
#   File "/usr/lib/python3.13/site-packages/debian/deb822.py", line 1761, in __init__
#     for line in filter(None, contents.splitlines()):   # type: str
#                              ^^^^^^^^^^^^^^^^^^^
# AttributeError: 'list' object has no attribute 'splitlines'