alternatives: Fix bug with priority default

[jiuka]

If neigther the priority nor the subcommands where specified the module decided to update the priority with the default value anyway. This resulted in the bug #4803 and #4804 when the subcommands have not been specified.

SUMMARY

Do not set the priority if the default value if the priority is not set.

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

alternatives

ADDITIONAL INFORMATION

[ansibullbot]

cc @mulby
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[felixfontein]

Thanks! Please add a changelog fragment.

[pilou-]

I added a very last nitpick but LGTM.

[felixfontein]

Hmm, when looking at the fix and the issues, I don't think this fixes #4803 or #4804. The problem seems to be that link for the subcommands is not correctly identified. For example, on RHEL 9, I get

$ alternatives --display man
man - status is auto.
 link currently points to /usr/bin/man.man-db
/usr/bin/man.man-db - priority 300
 slave apropos: /usr/bin/apropos.man-db
 slave whatis: /usr/bin/whatis.man-db
 slave man.1.gz: /usr/share/man/man1/man.man-db.1.gz
 slave apropos.1.gz: /usr/share/man/man1/apropos.man-db.1.gz
 slave whatis.1.gz: /usr/share/man/man1/whatis.man-db.1.gz
Current `best' version is /usr/bin/man.man-db.

This gives:

>>> alternative_regex.findall(out)
[('/usr/bin/man.man-db', '300', '\n slave apropos: /usr/bin/apropos.man-db\n slave whatis: /usr/bin/whatis.man-db\n slave man.1.gz: /usr/share/man/man1/man.man-db.1.gz\n slave apropos.1.gz: /usr/share/man/man1/apropos.man-db.1.gz\n slave whatis.1.gz: /usr/share/man/man1/whatis.man-db.1.gz')]
>>> path, prio, subcmd = alternative_regex.findall(out)[0]
>>> path
'/usr/bin/man.man-db'
>>> prio
'300'
>>> subcmd
'\n slave apropos: /usr/bin/apropos.man-db\n slave whatis: /usr/bin/whatis.man-db\n slave man.1.gz: /usr/share/man/man1/man.man-db.1.gz\n slave apropos.1.gz: /usr/share/man/man1/apropos.man-db.1.gz\n slave whatis.1.gz: /usr/share/man/man1/whatis.man-db.1.gz'
>>> subcmd_regex.findall(subcmd)
[('apropos', '/usr/bin/apropos.man-db'), ('whatis', '/usr/bin/whatis.man-db'), ('man.1.gz', '/usr/share/man/man1/man.man-db.1.gz'), ('apropos.1.gz', '/usr/share/man/man1/apropos.man-db.1.gz'), ('whatis.1.gz', '/usr/share/man/man1/whatis.man-db.1.gz')]
>>> subcmd_path_link_regex = re.compile(r'^\s*slave (\S+) is (.*)$', re.MULTILINE)
>>> subcmd_path_link_regex.findall(out)
[]

Thus subcmd_path_map is an empty map, and

        for path, prio, subcmd in alternative_regex.findall(display_output):
            self.current_alternatives[path] = dict(
                priority=int(prio),
                subcommands=[dict(
                    name=name,
                    path=spath,
                    link=subcmd_path_map.get(name)
                ) for name, spath in subcmd_regex.findall(subcmd) if spath != '(null)']
            )

produces dictionaries with link=None. The None entries are removed by module.run_command(), resulting in the missing options reported in the issues.

The output was a bit more interesting on RHEL8.5 we use in CI for python3:

$ alternatives --display python3
python3 - status is auto.
 link currently points to /usr/bin/python3.6
/usr/bin/python3.6 - priority 1000000
 slave easy_install-3: /usr/bin/easy_install-3.6
 slave pip-3: /usr/bin/pip-3.6
 slave pip3: /usr/bin/pip3.6
 slave pydoc-3: /usr/bin/pydoc3.6
 slave pydoc3: /usr/bin/pydoc3.6
 slave python3-config: /usr/bin/python3.6-config
 slave pyvenv-3: /usr/bin/pyvenv-3.6
 slave python3-man: /usr/share/man/man1/python3.6.1.gz
/usr/bin/python3.8 - priority 3800
 slave easy_install-3: /usr/bin/easy_install-3.8
 slave pip-3: /usr/bin/pip-3.8
 slave pip3: /usr/bin/pip3.8
 slave pydoc-3: /usr/bin/pydoc3.8
 slave pydoc3: /usr/bin/pydoc3.8
 slave python3-config: /usr/bin/python3.8-config
 slave pyvenv-3: (null)
 slave python3-man: /usr/share/man/man1/python3.8.1.gz
Current `best' version is /usr/bin/python3.6.

The output on Ubuntu 20.04 and 22.04 is different:

$ update-alternatives --display java
java - auto mode
  link best version is /usr/lib/jvm/java-11-openjdk-amd64/bin/java
  link currently points to /usr/lib/jvm/java-11-openjdk-amd64/bin/java
  link java is /usr/bin/java
  slave java.1.gz is /usr/share/man/man1/java.1.gz
/usr/lib/jvm/java-11-openjdk-amd64/bin/java - priority 1111
  slave java.1.gz: /usr/lib/jvm/java-11-openjdk-amd64/man/man1/java.1.gz
/usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java - priority 1081
  slave java.1.gz: /usr/lib/jvm/java-8-openjdk-amd64/jre/man/man1/java.1.gz

So the problem here isn't the default value for priority, but that on RHEL the module cannot identify the links it needs.

[felixfontein]

Ok, so this does fix a bug, but not the bug reported in the issues. Let's merge this anyway, but we need a fix for these issues as well...

[patchback]

Backport to stable-5: 💚 backport PR created

✅ Backport PR branch: patchback/backports/stable-5/57e83ac80b727c472d0c3911d9189ae667feb110/pr-4810

Backported as #4835

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[felixfontein]

Let's fix the issues in another PR.