Attempt at having more useful errors for plugin setup

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

slixmpp_omemo/__init__.py

@@ -32,14 +32,17 @@ from .stanza import Bundle, Devices, Device, Encrypted, Key, PreKeyPublic
 
 log = logging.getLogger(__name__)
 
-HAS_OMEMO = True
+HAS_OMEMO = False
+HAS_OMEMO_BACKEND = False
 try:
     import omemo.exceptions
     from omemo import SessionManager, ExtendedPublicBundle, DefaultOTPKPolicy
     from omemo.util import generateDeviceID
     from omemo.implementations import JSONFileStorage
     from omemo.backends import Backend
+    HAS_OMEMO = True
     from omemo_backend_signal import BACKEND as SignalBackend
+    HAS_OMEMO_BACKEND = True
 except (ImportError,):
     class Backend:
         pass
@@ -50,8 +53,6 @@ except (ImportError,):
     class SignalBackend:
         pass
 
-    HAS_OMEMO = False
-
 TRUE_VALUES = {True, 'true', '1'}
 PUBLISH_OPTIONS_NODE = 'http://jabber.org/protocol/pubsub#publish-options'
 PUBSUB_ERRORS = 'http://jabber.org/protocol/pubsub#errors'
@@ -186,15 +187,21 @@ class XEP_0384(BasePlugin):
         'omemo_backend': SignalBackend,
     }
 
-    backend_loaded = HAS_OMEMO
+    backend_loaded = HAS_OMEMO and HAS_OMEMO_BACKEND
 
     # OMEMO Bundles used for encryption
     bundles = {}  # type: Dict[str, Dict[int, ExtendedPublicBundle]]
 
     def plugin_init(self) -> None:
         if not self.backend_loaded:
-            log.info("xep_0384 cannot be loaded as the backend omemo library "
-                     "is not available")
+            log_str = ("xep_0384 cannot be loaded as the backend omemo library "
+                       "is not available. ")
+            if not HAS_OMEMO_BACKEND:
+                log_str += ("Make sure you have a python OMEMO backend "
+                            "(python-omemo-backend-signal) installed")
+            else:
+                log_str += "Make sure you have the python OMEMO library installed."
+            log.error(log_str)
             raise PluginCouldNotLoad
 
         if not self.data_dir: