Description of problem:

The python3-apt package does not work without /usr/bin/dpkg (provided by “dpkg”) and, to a lesser degree, /usr/bin/dpkg-source (provided by “dpkg-dev”).

Version-Release number of selected component (if applicable): 2.2.0-1.fc34


How reproducible:

Here I demonstrate the problem with diffoscope, but I find that there is no bug in diffoscope.

Steps to Reproduce:
1. $ sudo dnf install diffoscope
2. $ diffoscope --help

Actual results:

> Traceback (most recent call last):
>   File "/usr/lib/python3.9/site-packages/diffoscope/main.py", line 737, in main
>     parsed_args = parser.parse_args(args)
>   File "/usr/lib64/python3.9/argparse.py", line 1820, in parse_args
>     args, argv = self.parse_known_args(args, namespace)
>   File "/usr/lib64/python3.9/argparse.py", line 1853, in parse_known_args
>     namespace, args = self._parse_known_args(args, namespace)
>   File "/usr/lib64/python3.9/argparse.py", line 2062, in _parse_known_args
>     start_index = consume_optional(start_index)
>   File "/usr/lib64/python3.9/argparse.py", line 2002, in consume_optional
>     take_action(action, args, option_string)
>   File "/usr/lib64/python3.9/argparse.py", line 1930, in take_action
>     action(self, namespace, argument_values, option_string)
>   File "/usr/lib64/python3.9/argparse.py", line 1094, in __call__
>     parser.print_help()
>   File "/usr/lib64/python3.9/argparse.py", line 2550, in print_help
>     self._print_message(self.format_help(), file)
>   File "/usr/lib64/python3.9/argparse.py", line 2534, in format_help
>     return formatter.format_help()
>   File "/usr/lib/python3.9/site-packages/diffoscope/main.py", line 487, in format_help
>     ComparatorManager().format_descriptions(),
>   File "/usr/lib/python3.9/site-packages/diffoscope/comparators/__init__.py", line 123, in __init__
>     self.reload()
>   File "/usr/lib/python3.9/site-packages/diffoscope/comparators/__init__.py", line 134, in reload
>     mod = importlib.import_module(
>   File "/usr/lib64/python3.9/importlib/__init__.py", line 127, in import_module
>     return _bootstrap._gcd_import(name[level:], package, level)
>   File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
>   File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
>   File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
>   File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
>   File "<frozen importlib._bootstrap_external>", line 850, in exec_module
>   File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
>   File "/usr/lib/python3.9/site-packages/diffoscope/comparators/debian.py", line 24, in <module>
>     from debian.deb822 import Dsc, Deb822
>   File "/usr/lib/python3.9/site-packages/debian/deb822.py", line 283, in <module>
>     import debian.debian_support
>   File "/usr/lib/python3.9/site-packages/debian/debian_support.py", line 46, in <module>
>     apt_pkg.init()
> apt_pkg.Error: W:Unable to read /etc/apt/apt.conf.d/ - DirectoryExists (2: No such file or directory), E:Unable to determine a suitable packaging system type                                                                                                                      

Expected results:

> usage: diffoscope [--debug] [--pdb] [--status-fd FD] [--progress]
>                   [--no-default-limits] [--text OUTPUT_FILE]
>                   [--text-color WHEN] [--output-empty] [--html OUTPUT_FILE]
>                   [--html-dir OUTPUT_DIR] [--css URL] [--jquery URL]
> […]
> bugs/issues:
>                         <https://salsa.debian.org/reproducible-builds/diffoscope/issues>

Additional info:


Simply creating the apt configuration directory,

> $ mkdir -p /etc/apt/apt.conf.d

makes little difference. The traceback is the same; the warning disappears but the error remains.

Installing “dpkg” fixes the problem. Removing python3-apt (which is a weak dependency of python3-debian) *also* fixes the problem.

-----

The diffoscope package depends on python3-debian, which has a weak dependency on python3-apt. The python-debian package appears to have a fallback for when python-apt is not installed (ImportError on apt_pkg), but not for when apt_pkg.init() fails this way.

-----

In the python-apt source tree:

> $ grep -ErnI "['\"]dpkg" apt
apt/cache.py:140:                               os.path.join(rootdir, "usr", "bin", "dpkg"))
> apt/cache.py:763:        'dpkg --configure -a' as root.
> apt/debfile.py:725:            return os.spawnlp(os.P_WAIT, "dpkg", "dpkg", "-i", self.filename)
> apt/package.py:943:            subprocess.check_call(["dpkg-source", "-x", dsc, outdir])
> apt/progress/base.py:239:                os._exit(os.spawnlp(os.P_WAIT, "dpkg", "dpkg", "--status-fd",

My conclusion is that runtime dependencies on these command-line tools should be added to python3-apt, i.e.,

> Requires:       /usr/bin/dpkg
> Requires:       /usr/bin/dpkg-source