refactor: port all sys.exit over to kas exceptions

This patch replaces all direct invocations of sys.exit outside of the
main invocation to KasUserError based exceptions. By that, only one
method for returning is used and return codes can be handled
consistently. In addition, this makes it possible to handle specific
errors differently.

Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas/plugins/menu.py

@@ -69,7 +69,6 @@
 import logging
 import os
 import pprint
-import sys
 import yaml
 from kconfiglib import Kconfig, Symbol, Choice, expr_value, TYPE_TO_STR, \
     MENU, COMMENT, STRING, BOOL, INT, HEX, UNKNOWN
@@ -78,6 +77,7 @@ from kas.context import create_global_context
 from kas.config import CONFIG_YAML_FILE
 from kas.includehandler import load_config as load_config_yaml
 from kas.plugins.build import Build
+from kas.kasusererror import KasUserError
 
 try:
     from snack import SnackScreen, EntryWindow, ButtonChoiceWindow, \
@@ -92,10 +92,18 @@ __copyright__ = \
     'Copyright (c) Siemens AG, 2021'
 
 
+class VariableTypeError(KasUserError):
+    pass
+
+
+class MissingModuleError(KasUserError):
+    pass
+
+
 def check_sym_is_string(sym):
     if sym.type != STRING:
-        logging.error('Variable %s must be of string type', sym.name)
-        sys.exit(1)
+        raise VariableTypeError('Variable {} must be of string type'
+                                .format(sym.name))
 
 
 def str_representer(dumper, data):
@@ -175,10 +183,9 @@ class Menu:
                 elif sym.type == HEX:
                     menu_configuration[symname] = int(symvalue, 16)
                 else:
-                    logging.error(
-                        'Configuration variable %s uses unsupported type',
-                        symname)
-                    sys.exit(1)
+                    raise VariableTypeError(
+                        'Configuration variable {} uses unsupported type'
+                        .format(symname))
 
             if symname.startswith('KAS_INCLUDE_'):
                 check_sym_is_string(sym)
@@ -241,9 +248,8 @@ class Menu:
 
     def run(self, args):
         if not newt_available:
-            logging.error(
+            raise MissingModuleError(
                 'Menu plugin requires \'python3-newt\' distribution package.')
-            sys.exit(1)
 
         ctx = create_global_context(args)