unbreq dies at the end: dnf remove returned non-zero exit status 2

[hroncok]

Hi. I tried to build python3.15 from rawhide (actually from a planned update https://src.fedoraproject.org/rpms/python3.15/pull-request/38) with the unbreq plugin:

$ mock -r fedora-rawhide-x86_64 --enable-plugin=unbreq python3.15-3.15.0~a5-1.fc44.src.rpm
...
INFO: enabled unbreq plugin (postdeps)
INFO: unbreq plugin: detected 'relatime' mount option, setting access times of files under /var/lib/mock/fedora-rawhide-x86_64/root to 0
...

It finished the build of Python and dies:

...
Finish: rpmbuild python3.15-3.15.0~a5-1.fc44.src.rpm
Finish: build phase for python3.15-3.15.0~a5-1.fc44.src.rpm
INFO: enabled unbreq plugin (postbuild)
ERROR: Exception(python3.15-3.15.0~a5-1.fc44.src.rpm) Config(fedora-rawhide-x86_64) 91 minutes 46 seconds
INFO: Results and/or logs in: /var/lib/mock/fedora-rawhide-x86_64/result
ERROR: Command '/usr/bin/systemd-nspawn --quiet --pipe -D /var/lib/mock/fedora-rawhide-x86_64-bootstrap/root --bind /var/lib/mock/fedora-rawhide-x86_64/root /usr/bin/dnf --installroot /var/lib/mock/fedora-rawhide-x86_64/root --setopt protected_packages= --assumeno remove' returned non-zero exit status 2.
Traceback (most recent call last):
  File "/usr/libexec/mock/mock", line 1132, in <module>
    exitStatus = main()
  File "/usr/lib/python3.14/site-packages/mockbuild/trace_decorator.py", line 93, in trace
    result = func(*args, **kw)
  File "/usr/libexec/mock/mock", line 884, in main
    result = run_command(options, args, config_opts, commands, buildroot)
  File "/usr/lib/python3.14/site-packages/mockbuild/trace_decorator.py", line 93, in trace
    result = func(*args, **kw)
  File "/usr/libexec/mock/mock", line 1006, in run_command
    mockbuild.rebuild.do_rebuild(config_opts, commands, buildroot, options, srpms)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.14/site-packages/mockbuild/trace_decorator.py", line 93, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.14/site-packages/mockbuild/rebuild.py", line 85, in do_rebuild
    rebuild_generic(srpms, commands, buildroot, config_opts, cmd=build,
    ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                    post=post_build, clean=clean)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.14/site-packages/mockbuild/trace_decorator.py", line 93, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.14/site-packages/mockbuild/rebuild.py", line 25, in rebuild_generic
    ret = cmd(item)
  File "/usr/lib/python3.14/site-packages/mockbuild/rebuild.py", line 66, in build
    commands.build(srpm, timeout=config_opts['rpmbuild_timeout'],
    ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                   check=config_opts['check'], spec=options.spec)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.14/site-packages/mockbuild/trace_decorator.py", line 93, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.14/site-packages/mockbuild/backend.py", line 346, in build
    self.plugins.call_hooks('postbuild')
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
  File "/usr/lib/python3.14/site-packages/mockbuild/trace_decorator.py", line 93, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.14/site-packages/mockbuild/plugin.py", line 81, in call_hooks
    hook(*args, **kwargs)
    ~~~~^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.14/site-packages/mockbuild/plugins/unbreq.py", line 362, in _PostBuildHook
    self.resolve_buildrequires()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/usr/lib/python3.14/site-packages/mockbuild/plugins/unbreq.py", line 226, in resolve_buildrequires
    removed_packages = self.try_remove([v for vs in brs_can_be_removed for v in vs[1]] + providers)
  File "/usr/lib/python3.14/site-packages/mockbuild/plugins/unbreq.py", line 159, in try_remove
    raise subprocess.CalledProcessError(
        process.returncode, " ".join(process.args), process.stdout, process.stderr
    )
subprocess.CalledProcessError: Command '/usr/bin/systemd-nspawn --quiet --pipe -D /var/lib/mock/fedora-rawhide-x86_64-bootstrap/root --bind /var/lib/mock/fedora-rawhide-x86_64/root /usr/bin/dnf --installroot /var/lib/mock/fedora-rawhide-x86_64/root --setopt protected_packages= --assumeno remove' returned non-zero exit status 2.

I don't see the stderr from dnf, but exit code 2 probably means there was no argument for the package to remove:

$ LANG=C dnf remove
Missing positional argument "specs" for command "remove". Add "--help" for more information about the arguments.
$ echo $?
2

Seems like the plugin tries to remove a package, but it does not provide a package to remove :/

mock-6.6-1.fc43.noarch
mock-core-configs-43.3-1.fc43.noarch

[xsuchy]

cc @mkoncek

[hroncok]

I see there was a significant refactor after mock-6.6-1. I can try later with the current version.

However, speaking of the version I have, I think the try_remove either needs to handle empty packages differently, or it should never be called with empty packages. I will try that.

[mkoncek]

Hi, @hroncok, moreover, there is a PR to log the command outputs: #1686
I will try to reproduce the failure. Thanks for the report.

[hroncok]

    def try_remove(self, packages: list[str]) -> list[str]:
        """
        Try to remove `packages` and obtain all the packages (NVRs) that would be removed.
        """

        if not packages:
            return []

Adding this check solved the issue for me. However, as said, not sure if it is needed after the refactor.

[mkoncek]

Confirming that dnf remove was called with no arguments:

DEBUG: unbreq plugin: Executing command: ['/usr/bin/systemd-nspawn', '--quiet', '--ephemeral', '--pipe', '-D', '/var/lib/mock/fedora-rawhide-x86_64-bootstrap/root', '--bind', '/var/lib/mock/fedora-rawhide-x86_64/root', '/usr/bin/dnf5', '--installroot', '/var/lib/mock/fedora-rawhide-x86_64/root', '--setopt', 'protected_packages=', '--assumeno', 'remove']

I think there is a reason why I didn't put the check into the function though. It probably means that one of the BuildRequires is not provided by any installed RPM and I did not account for that...

[mkoncek]

(python-wheel-wheel if python-setuptools-wheel < 71) provided by: []

So, I think there is a valid case of a BuildRequires not provided by any installed RPM and the plugin should recognize it.

[hroncok]

Thanks for identifying the cause!