Navigation and dashboard: Do not crash page if a plugin fails

Generally, I don't think it's a good approach for plugins to fail
silently. A missing menu item or button is a weird failure mode, people
will search for it and the system will feel buggy. However, a single bug
in a plugin should not cause the entire system to feel "down" since the
entire backend can't load, not even the dashboard right after login. So
here, I think the trade-off is warranted to fail silently -- and
escalate quickly via Sentry.

src/pretix/base/signals.py

@@ -147,7 +147,7 @@ class PluginSignal(Generic[T], django.dispatch.Signal):
     def _is_receiver_active(self, sender, receiver):
         return is_receiver_active(sender, receiver)
 
-    def send(self, sender: T, **named) -> List[Tuple[Callable, Any]]:
+    def send(self, sender: T, skip_exceptions=False, **named) -> List[Tuple[Callable, Any]]:
         """
         Send signal from sender to all connected receivers that belong to
         plugins enabled for the given event / organizer.
@@ -164,8 +164,19 @@ class PluginSignal(Generic[T], django.dispatch.Signal):
 
         for receiver in self._live_receivers(sender)[0]:
             if self._is_receiver_active(sender, receiver):
-                response = receiver(signal=self, sender=sender, **named)
-                responses.append((receiver, response))
+                try:
+                    response = receiver(signal=self, sender=sender, **named)
+                except Exception as e:
+                    if skip_exceptions:
+                        logger.exception("Signal handler skipped due to exception")
+                        if settings.SENTRY_ENABLED:
+                            import sentry_sdk
+
+                            sentry_sdk.capture_exception(e)
+                    else:
+                        raise
+                else:
+                    responses.append((receiver, response))
         return responses
 
     def send_chained(self, sender: T, chain_kwarg_name, **named) -> List[Tuple[Callable, Any]]:
@@ -312,6 +323,30 @@ class OrganizerPluginSignal(PluginSignal[Organizer]):
 
 
 class GlobalSignal(django.dispatch.Signal):
+    def send(self, sender, skip_exceptions=False, **named):
+        if (
+                not self.receivers
+                or self.sender_receivers_cache.get(sender) is NO_RECEIVERS
+        ):
+            return []
+        responses = []
+        sync_receivers, _ = self._live_receivers(sender)
+        for receiver in sync_receivers:
+            try:
+                response = receiver(signal=self, sender=sender, **named)
+            except Exception as e:
+                if skip_exceptions:
+                    logger.exception("Signal handler skipped due to exception")
+                    if settings.SENTRY_ENABLED:
+                        import sentry_sdk
+
+                        sentry_sdk.capture_exception(e)
+                else:
+                    raise
+            else:
+                responses.append((receiver, response))
+        return responses
+
     def send_chained(self, sender: Event, chain_kwarg_name, **named) -> List[Tuple[Callable, Any]]:
         """
         Send signal from sender to all connected receivers. The return value of the first receiver

src/pretix/control/navigation.py

@@ -135,7 +135,7 @@ def get_event_navigation(request: HttpRequest):
         # It would be better to allow plugins to handle the permission themselves, but for backwards compatibility
         # we need to have it in the "if" statement
         event_settings += sorted(
-            sum((list(a[1]) for a in nav_event_settings.send(request.event, request=request)), []),
+            sum((list(a[1]) for a in nav_event_settings.send(request.event, skip_exceptions=True, request=request)), []),
             key=lambda r: r['label']
         )
     if event_settings:
@@ -487,7 +487,7 @@ def get_global_navigation(request):
         })
 
     merge_in(nav, sorted(
-        sum((list(a[1]) for a in nav_global.send(request, request=request)), []),
+        sum((list(a[1]) for a in nav_global.send(request, skip_exceptions=True, request=request)), []),
         key=lambda r: (1 if r.get('parent') else 0, r['label'])
     ))
     return nav
@@ -718,7 +718,7 @@ def get_organizer_navigation(request):
         })
 
     merge_in(nav, sorted(
-        sum((list(a[1]) for a in nav_organizer.send(request.organizer, request=request, organizer=request.organizer)),
+        sum((list(a[1]) for a in nav_organizer.send(request.organizer, skip_exceptions=True, request=request, organizer=request.organizer)),
             []),
         key=lambda r: (1 if r.get('parent') else 0, r['label'])
     ))

src/pretix/control/views/dashboards.py

@@ -370,7 +370,7 @@ def event_index(request, organizer, event):
 
     widgets = []
     if can_view_orders:
-        for r, result in event_dashboard_widgets.send(sender=request.event, subevent=subevent, lazy=True):
+        for r, result in event_dashboard_widgets.send(sender=request.event, subevent=subevent, lazy=True, skip_exceptions=True):
             widgets.extend(result)
 
     ctx = {
@@ -406,7 +406,7 @@ def event_index_widgets_lazy(request, organizer, event):
                                                         request=request)
     widgets = []
     if can_view_orders:
-        for r, result in event_dashboard_widgets.send(sender=request.event, subevent=subevent, lazy=False):
+        for r, result in event_dashboard_widgets.send(sender=request.event, subevent=subevent, lazy=False, skip_exceptions=True):
             widgets.extend(result)
 
     return build_json_response(widgets)
@@ -666,7 +666,7 @@ def user_index_widgets_lazy(request):
 
 def user_index(request):
     widgets = []
-    for r, result in user_dashboard_widgets.send(request, user=request.user):
+    for r, result in user_dashboard_widgets.send(request, skip_exceptions=True, user=request.user):
         widgets.extend(result)
 
     ctx = {