Don't drop only partially supported GTFS-RT messages

Previously all messages containing unsupported fields like (alert or
vehicle) were ignored, even if they contained an understandable
trip_update.

Now all possible warnings are emitted, not just the first fatal one.

This commit also changes the debug output to show the names of the
relevant fields to make it easier to debug GTFS-RT feeds without looking
at the MOTIS source code.

src/rt/gtfsrt_update.cc

@@ -268,37 +268,54 @@ statistics gtfsrt_update_msg(timetable const& tt,
   span->SetAttribute("nigiri.gtfsrt.total_entities", msg.entity_size());
 
   for (auto const& entity : msg.entity()) {
-    if (entity.has_is_deleted() && entity.is_deleted()) {
+    bool skip = false;
+    if (int count = entity.has_alert() + entity.has_trip_update() +
+                    entity.has_vehicle();
+        count > 1) {
       log(log_lvl::error, "rt.gtfs.unsupported",
-          "unsupported deleted (tag={}, id={})", tag, entity.id());
-      ++stats.unsupported_deleted_;
-      continue;
-    } else if (entity.has_alert()) {
+          R"(message has multiple of "trip_update", "vehicle" and "alert" set. This is discouraged by the spec (https://gtfs.org/documentation/realtime/reference/#message-feedentity) (tag={}, id={}))",
+          tag, entity.id());
+    }
+    // no continue here so we don't skip as long as it also has a trip_update
+    if (entity.has_vehicle()) {
+      log(log_lvl::error, "rt.gtfs.unsupported",
+          R"(ignoring unsupported "vehicle" field (tag={}, id={}))", tag,
+          entity.id());
+      ++stats.unsupported_vehicle_;
+    }
+    // no continue here so we don't skip as long as it also has a trip_update
+    if (entity.has_alert()) {
       log(log_lvl::error, "rt.gtfs.unsupported",
-          "unsupported alert (tag={}, id={})", tag, entity.id());
+          R"(ignoring unsupported "alert" field (tag={}, id={}))", tag,
+          entity.id());
       ++stats.unsupported_alert_;
-      continue;
-    } else if (entity.has_vehicle()) {
+    }
+    if (entity.has_is_deleted() && entity.is_deleted()) {
       log(log_lvl::error, "rt.gtfs.unsupported",
-          "unsupported vehicle (tag={}, id={})", tag, entity.id());
-      ++stats.unsupported_vehicle_;
-      continue;
-    } else if (!entity.has_trip_update()) {
+          R"(unsupported "id_deleted" field (tag={}, id={}), skipping message)",
+          tag, entity.id());
+      ++stats.unsupported_deleted_;
+      skip = true;
+    }
+    if (!entity.has_trip_update()) {
       log(log_lvl::error, "rt.gtfs.unsupported",
-          "unsupported no trip update (tag={}, id={})", tag, entity.id());
+          R"(unsupported: no "trip_update" field (tag={}, id={}), skipping message)",
+          tag, entity.id());
       ++stats.no_trip_update_;
-      continue;
-    } else if (!entity.trip_update().has_trip()) {
+      skip = true;
+    }
+    if (!entity.trip_update().has_trip()) {
       log(log_lvl::error, "rt.gtfs.unsupported",
-          "unsupported no trip in trip update (tag={}, id={})", tag,
-          entity.id());
+          R"(unsupported: no "trip" field in "trip_update" field (tag={}, id={}), skipping message)",
+          tag, entity.id());
       ++stats.trip_update_without_trip_;
       continue;
     } else if (!entity.trip_update().trip().has_trip_id()) {
       log(log_lvl::error, "rt.gtfs.unsupported",
-          "unsupported trip without trip_id (tag={}, id={})", tag, entity.id());
+          R"(unsupported: no "trip_id" field in "trip_update.trip" (tag={}, id={}), skipping message)",
+          tag, entity.id());
       ++stats.unsupported_no_trip_id_;
-      continue;
+      skip = true;
     } else if (entity.trip_update().trip().schedule_relationship() !=
                    gtfsrt::TripDescriptor_ScheduleRelationship_SCHEDULED &&
                entity.trip_update().trip().schedule_relationship() !=
@@ -309,6 +326,10 @@ statistics gtfsrt_update_msg(timetable const& tt,
               entity.trip_update().trip().schedule_relationship()),
           tag, entity.id());
       ++stats.unsupported_schedule_relationship_;
+      skip = true;
+    }
+
+    if (skip) {
       continue;
     }