When `transitOnly` is used, a user should be able to specify a direct mode to filter with that does not appear in the results

[VillePihlava]

Is your feature request related to a problem? Please describe.

When the StreetMode is unset, logic in the RoutingWorker sets the direct mode to WALK for filtering. The WALK mode direct search result is filtered away before returning the results to the user.

OpenTripPlanner/application/src/main/java/org/opentripplanner/apis/gtfs/mapping/routerequest/ModePreferencesMapper.java

Lines 28 to 30 in 9ee0c58

	if (Boolean.TRUE.equals(modesInput.getGraphQLTransitOnly())) {
	journey.direct().setMode(StreetMode.NOT_SET);
	} else if (direct != null) {

OpenTripPlanner/application/src/main/java/org/opentripplanner/routing/algorithm/RoutingWorker.java

Line 98 in 9ee0c58

request.journey().direct().setMode(emptyDirectModeHandler.resolveDirectMode());

OpenTripPlanner/application/src/main/java/org/opentripplanner/routing/algorithm/RoutingWorker.java

Line 137 in 9ee0c58

emptyDirectModeHandler.removeWalkAllTheWayResults() ||

Instead of setting the direct mode to WALK when the direct mode is unset, it should be configurable.

Goal / high level use-case

For example, with CAR mode transit results it would be useful to filter based on the CAR direct mode. With paging the default WALK direct mode search is skipped. However, it would be useful to be able to specify a direct mode with transitOnly that does not appear in the results with paging as well. Currently only a direct + transit search with filtering is possible when using paging.

Additional context

This PR removed the default WALK direct search for filtering when used with paging: #6474

[miklcct]

Can you please further explain why you want a direct mode when transitOnly is set? Even in such a case, shouldn't the direct mode be inferred from the interchange mode used in the transit search, as it implies bringing your vehicle for the whole journey?

[VillePihlava]

@miklcct this was something that came up during a discussion about an addition to paging with @optionsome and @t2gran. If you want additional context, please look at issue #6083, for example. There are reasons you would want to filter transitOnly results, however, the problem is that determining what to filter with can be difficult. Issue #6083 suggests a matrix that determines what mode to filter with.