Handle a missing session folder at some places.

qutebrowser/app.py

@@ -44,7 +44,7 @@ except ImportError:
 import qutebrowser
 import qutebrowser.resources  # pylint: disable=unused-import
 from qutebrowser.completion.models import instances as completionmodels
-from qutebrowser.commands import cmdutils, runners
+from qutebrowser.commands import cmdutils, runners, cmdexc
 from qutebrowser.config import style, config, websettings, configexc
 from qutebrowser.browser import quickmarks, cookies, cache, adblock, history
 from qutebrowser.browser.network import qutescheme, proxy, networkmanager
@@ -728,7 +728,11 @@ class Application(QApplication):
     @cmdutils.register(instance='app')
     def restart(self):
         """Restart qutebrowser while keeping existing tabs open."""
+        try:
             ok = self._do_restart(session='_restart')
+        except sessions.SessionError as e:
+            log.destroy.exception("Failed to save session!")
+            raise cmdexc.CommandError("Failed to save session: {}!".format(e))
         if ok:
             self.shutdown()
 

qutebrowser/completion/models/miscmodels.py

@@ -20,7 +20,7 @@
 """Misc. CompletionModels."""
 
 from qutebrowser.config import config, configdata
-from qutebrowser.utils import objreg
+from qutebrowser.utils import objreg, log
 from qutebrowser.commands import cmdutils
 from qutebrowser.completion.models import base
 
@@ -120,6 +120,9 @@ class SessionCompletionModel(base.BaseCompletionModel):
     def __init__(self, parent=None):
         super().__init__(parent)
         cat = self.new_category("Sessions")
+        try:
             for name in objreg.get('session-manager').list_sessions():
                 if not name.startswith('_'):
                     self.new_item(cat, name)
+        except OSError:
+            log.completion.exception("Failed to list sessions!")

qutebrowser/misc/sessions.py

@@ -375,6 +375,10 @@ class SessionManager(QObject):
                                           name))
         try:
             self.delete(name)
-        except OSError as e:
+        except SessionNotFoundError as e:
+            log.misc.exception("Session not found!")
+            raise cmdexc.CommandError("Session {} not found".format(e))
+        except (OSError, SessionError) as e:
+            log.misc.exception("Error while deleting session!")
             raise cmdexc.CommandError("Error while deleting session: {}"
                                       .format(e))