src.python.jw.pkg.App: Add property distro_id

Add @property App.distro_id, returning the ID field of
/etc/os-release. It is supposed to be the most specific part of the
OS cascade.

Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/App.py

@@ -210,6 +210,7 @@ class App(Base):
         # -- Members without default values
         self.__opt_os: str|None = None
         self.__top_name: str|None = None
+        self.__distro_id: str|None = None
         self.__os_cascade: list[str]|None = None
         self.__res_cache = ResultCache()
         self.__topdir: str|None = None
@@ -251,6 +252,17 @@ class App(Base):
     def projs_root(self):
         return self.__projs_root
 
+    @property
+    def distro_id(self):
+        if self.__distro_id is None:
+            os_release = '/etc/os-release'
+            with open(os_release, 'r') as file:
+                m = re.search(r'^\s*ID\s*=\s*("?)([^"\n]+)\1\s*$', file.read(), re.MULTILINE)
+                if m is None:
+                    raise Exception(f'Could not read "ID=" from "{os_release}"')
+                self.__distro_id = m.group(2)
+        return self.__distro_id
+
     def find_dir(self, name: str, search_subdirs: list[str]=[], search_absdirs: list[str]=[], pretty: bool=True):
         return self.__find_dir(name, search_subdirs, search_absdirs, pretty)
 

src/python/jw/pkg/cmds/CmdDistro.py

@@ -18,14 +18,11 @@ class CmdDistro(CmdBase): # export
     def distro_id(self):
         if self.__id is None:
             if self.app.args.id is not None:
+                # The distribution ID requested by the command line
                 self.__id = self.app.args.id
             else:
-                os_release = '/etc/os-release'
-                with open(os_release, 'r') as file:
-                    m = re.search(r'^\s*ID\s*=\s*("?)([^"\n]+)\1\s*$', file.read(), re.MULTILINE)
-                    if m is None:
-                        raise Exception(f'Could not read "ID=" from "{os_release}"')
-                    self.__id = m.group(2)
+                # The ID of the distribution we run on
+                self.__id = self.app.distro_id
         return self.__id
 
     def add_arguments(self, p: ArgumentParser) -> None: