Add filter just for direct flex itineraries

src/main/java/org/opentripplanner/model/plan/Itinerary.java

@@ -164,6 +164,13 @@ public boolean isOnStreetAllTheWay() {
     return isStreetOnly();
   }
 
+  /**
+   * Returns true if this itinerary has only flex and walking legs.
+   */
+  public boolean isFlexAndWalkOnly() {
+    return legs.stream().allMatch(l -> l.isFlexibleTrip() || l.isWalkingLeg());
+  }
+
   /** TRUE if at least one leg is a transit leg. */
   public boolean hasTransit() {
     return legs

src/main/java/org/opentripplanner/routing/algorithm/filterchain/ItineraryListFilterChainBuilder.java

@@ -25,6 +25,7 @@
 import org.opentripplanner.routing.algorithm.filterchain.filters.street.RemoveNonTransitItinerariesBasedOnGeneralizedCost;
 import org.opentripplanner.routing.algorithm.filterchain.filters.street.RemoveParkAndRideWithMostlyWalkingFilter;
 import org.opentripplanner.routing.algorithm.filterchain.filters.street.RemoveWalkOnlyFilter;
+import org.opentripplanner.routing.algorithm.filterchain.filters.system.FlexSearchWindowFilter;
 import org.opentripplanner.routing.algorithm.filterchain.filters.system.NumItinerariesFilter;
 import org.opentripplanner.routing.algorithm.filterchain.filters.system.OutsideSearchWindowFilter;
 import org.opentripplanner.routing.algorithm.filterchain.filters.system.PagingFilter;
@@ -468,6 +469,7 @@ public ItineraryListFilterChain build() {
           filters,
           new OutsideSearchWindowFilter(earliestDepartureTime, searchWindow)
         );
+        addRemoveFilter(filters, new FlexSearchWindowFilter(earliestDepartureTime));
       }
 
       // Remove itineraries present in the page retrieved before this page/search.

src/main/java/org/opentripplanner/routing/algorithm/filterchain/filters/system/FlexSearchWindowFilter.java

@@ -0,0 +1,46 @@
+package org.opentripplanner.routing.algorithm.filterchain.filters.system;
+
+import java.time.Instant;
+import java.util.function.Predicate;
+import org.opentripplanner.model.plan.Itinerary;
+import org.opentripplanner.routing.algorithm.filterchain.framework.spi.RemoveItineraryFlagger;
+
+/**
+ * The flex router doesn't use the transit router's time window but nevertheless using it
+ * for filtering is useful when combining flex with transit.
+ * <p>
+ * The flex router also searches the previous day (arrive by) or the next one (depart after).
+ * If you didn't do it you could get yesterday's or tomorrow's results where you would not expect it.
+ */
+public class FlexSearchWindowFilter implements RemoveItineraryFlagger {
+
+  public static final String TAG = "outside-flex-window";
+
+  private final Instant earliestDepartureTime;
+
+  public FlexSearchWindowFilter(Instant earliestDepartureTime) {
+    this.earliestDepartureTime = earliestDepartureTime;
+  }
+
+  @Override
+  public String name() {
+    return TAG;
+  }
+
+  @Override
+  public Predicate<Itinerary> shouldBeFlaggedForRemoval() {
+    return it -> {
+      if (it.isFlexAndWalkOnly()) {
+        var time = it.startTime().toInstant();
+        return time.isBefore(earliestDepartureTime);
+      } else {
+        return false;
+      }
+    };
+  }
+
+  @Override
+  public boolean skipAlreadyFlaggedItineraries() {
+    return false;
+  }
+}

src/main/java/org/opentripplanner/routing/algorithm/filterchain/filters/system/OutsideSearchWindowFilter.java

@@ -7,8 +7,10 @@
 import org.opentripplanner.routing.algorithm.filterchain.framework.spi.RemoveItineraryFlagger;
 
 /**
- * This filter will remove all itineraries that are outside the search-window. In some
- * cases the access is time-shifted after the end of the search-window. These results
+ * This filter will remove all itineraries that are both search-window aware and outside the
+ * search-window. Only those that use transit are search-window, street and flex itineraries are not.
+ * <p>
+ * In some cases the access is time-shifted after the end of the search-window. These results
  * should appear again when paging to the next page. Hence, this filter will remove
  * such itineraries. The same is true for when paging to the previous page for arriveBy=true.
  * <p>

src/test/java/org/opentripplanner/model/plan/ItineraryTest.java

@@ -258,6 +258,12 @@ void bothPenalties() {
       );
     }
 
+    @Test
+    void flexAndWalk() {
+      assertFalse(itinerary().isFlexAndWalkOnly());
+      assertTrue(newItinerary(A).flex(T11_10, T11_20, B).build().isFlexAndWalkOnly());
+    }
+
     private static Itinerary itinerary() {
       return newItinerary(A).bus(1, T11_04, T11_14, B).build();
     }