Report a config error when trying to load credentials_mgr_class that …

…does't exist

osc/babysitter.py

@@ -151,7 +151,7 @@ def run(prg, argv=None):
             raise
         print(e, file=sys.stderr)
     except (oscerr.ConfigError, oscerr.NoConfigfile) as e:
-        print(e.msg, file=sys.stderr)
+        print(e, file=sys.stderr)
     except configparser.Error as e:
         print(e.message, file=sys.stderr)
     except oscerr.OscIOError as e:

osc/credentials.py

@@ -15,6 +15,9 @@
 except ImportError:
     gnomekeyring = None
 
+from . import conf
+from . import oscerr
+
 
 class AbstractCredentialsManagerDescriptor(object):
     def name(self):
@@ -184,7 +187,11 @@ def _process_options(self, options):
         self._backend_cls_name = options
 
     def _load_backend(self):
-        keyring_backend = keyring.core.load_keyring(self._backend_cls_name)
+        try:
+            keyring_backend = keyring.core.load_keyring(self._backend_cls_name)
+        except ModuleNotFoundError:
+            msg = "Invalid credentials_mgr_class: {}".format(self._backend_cls_name)
+            raise oscerr.ConfigError(msg, conf.config['conffile'])
         keyring.set_keyring(keyring_backend)
 
     @classmethod

osc/oscerr.py

@@ -22,6 +22,9 @@ def __init__(self, msg, fname):
         self.msg = msg
         self.file = fname
 
+    def __str__(self):
+        return "Error in config file {}\n   {}".format(self.file, self.msg)
+
 class ConfigMissingApiurl(ConfigError):
     """Exception raised when a apiurl does not exist in the config file"""
     def __init__(self, msg, fname, url):
@@ -46,6 +49,9 @@ def __init__(self, fname, msg):
         self.file = fname
         self.msg = msg
 
+    def __str__(self):
+        return "Config file cannot be found: {}\n   {}".format(self.file, self.msg)
+
 class ExtRuntimeError(OscBaseError):
     """Exception raised when there is a runtime error of an external tool"""
     def __init__(self, msg, fname):