Add a validation rule to check for correct trip to route pair after the addition of trip-to-trip and route-to-route transfers

[isabelle-dr]

Describe the problem

In Q4 2021, trip-to-trip and route-to-route transfers were added to the specification (google/transit#278).
The validator schema has been modified accordingly (in PR #1208).

These new fields contain the mentions "must" that should be translated to new validation rules. Here are the spec additions in transfers.txt.

1. in from_route_id and from_trip_id

If both from_trip_id and from_route_id are defined, the trip_id must belong to the route_id, and from_trip_id will take precedence.

2. in to_route_id and to_trip_id

If both to_trip_id and to_route_id are defined, the trip_id must belong to the route_id, and to_trip_id will take precedence.

Describe the new validation rule

For each trip_id and route_id set defined in transfers.txt, make sure that the trip belongs to the correct route.

Pseudo code:

If [from_trip_id and from_route_id are defined] OR [to_trip_id and to_route_id are defined]:
  If  no record exists in trips.txt with the trip_id and route_id defined (not entirely sure this is the best way to see if the trip belongs to the correct route):
             Trigger the notice.

Sample GTFS datasets

No response

Severity

ERROR because there is a mention of "must"

Additional context

No response