password_command failures are now fatal

CHANGELOG.rst

@@ -9,6 +9,12 @@ Package maintainers and users who have to manually update their installation
 may want to subscribe to `GitHub's tag feed
 <https://github.com/untitaker/vdirsyncer/tags.atom>`_.
 
+Version 0.5.3
+=============
+
+- ``password_command`` invocations with non-zero exit code are now fatal (and
+  will abort synchronization) instead of just producing a warning.
+
 Version 0.5.2
 =============
 

vdirsyncer/utils/password.py

@@ -4,7 +4,7 @@ import threading
 
 from . import expand_path
 from .compat import urlparse
-from .. import log
+from .. import exceptions, log
 from ..doubleclick import click, ctx
 
 logger = log.get(__name__)
@@ -115,7 +115,7 @@ def _password_from_command(username, host):
     try:
         stdout = subprocess.check_output(command + [username, host],
                                          universal_newlines=True)
-        return stdout.strip()
+        return stdout.strip('\n') or None
     except OSError as e:
-        logger.warning('Failed to execute command: {}\n{}'.
+        raise exceptions.UserError('Failed to execute command: {}\n{}'.
-                       format(' '.join(command), str(e)))
+                                   format(' '.join(command), str(e)))