sepolicy: set conf.substitutions['releasever'] to empty str when releasever is None

For some distributions (e.g. Yocto) that do not provide
system-release/distribution-release file, libdnf can not get releasever
variable, causing conf.substitutions['releasever'] to not be set.
This will cause 'sepolicy generate' command to fail with the following
error on these distributions:

$ sepolicy generate --init /usr/local/bin/foo
Traceback (most recent call last):
  File "/usr/bin/sepolicy", line 702, in <module>
    args.func(args)
  File "/usr/bin/sepolicy", line 569, in generate
    mypolicy.gen_writeable()
  File "/usr/lib/python3.12/site-packages/sepolicy/generate.py", line 1302, in gen_writeable
    self.__extract_rpms()
  File "/usr/lib/python3.12/site-packages/sepolicy/generate.py", line 1268, in __extract_rpms
    base.read_all_repos()
  File "/usr/lib/python3.12/site-packages/dnf/base.py", line 554, in read_all_repos
    for repo in reader:
                ^^^^^^
  File "/usr/lib/python3.12/site-packages/dnf/conf/read.py", line 42, in __iter__
    for r in self._get_repos(self.conf.config_file_path):
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/dnf/conf/read.py", line 109, in _get_repos
    parser.setSubstitutions(substs)
  File "/usr/lib/python3.12/site-packages/libdnf/conf.py", line 1643, in setSubstitutions
    return _conf.ConfigParser_setSubstitutions(self, substitutions)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: in method 'ConfigParser_setSubstitutions', argument 2 of type 'std::map< std::string,std::string,std::less< std::string >,std::allocator< std::pair< std::string const,std::string > > > const &'

Set conf.substitutions['releasever'] to empty str if releasever is None.

Signed-off-by: Yi Zhao <[email protected]>

Author: yizhao1

python/sepolicy/sepolicy/generate.py

@@ -1265,6 +1265,9 @@ def __extract_rpms(self):
         import dnf
 
         with dnf.Base() as base:
+            if base.conf.substitutions.get('releasever') is None:
+                base.conf.substitutions['releasever'] = ''
+
             base.read_all_repos()
             base.fill_sack(load_system_repo=True)