Only run step collapsing based on original waypoints parameter (#4829)

CHANGELOG.md

@@ -1,5 +1,7 @@
 # UNRELEASED
   - Changes from 5.15.0:
+    - Bugfixes:
+      - FIXED: Segfault in map matching when RouteLeg collapsing code is run on a match with multiple submatches
     - Profile:
       - FIXED: `highway=service` will now be used for restricted access, `access=private` is still disabled for snapping.
       - ADDED #4775: Exposes more information to the turn function, now being able to set turn weights with highway and access information of the turn as well as other roads at the intersection [#4775](https://github.com/Project-OSRM/osrm-backend/issues/4775)

features/testbot/matching.feature

@@ -603,3 +603,26 @@ Feature: Basic Map Matching
         When I match I should get
             | trace | timestamps | code    |
             | ab1d  | 0 1 2 3    | NoMatch |
+
+    Scenario: Regression test - avoid collapsing legs of a tidied split trace
+        Given a grid size of 20 meters
+        Given the node map
+            """
+            a--b--f
+               |
+               |
+               e--c---d--g
+            """
+        Given the query options
+        | tidy | true |
+
+        And the ways
+            | nodes | oneway |
+            | abf   | no     |
+            | be    | no     |
+            | ecdg  | no     |
+
+        When I match I should get
+        | trace    | timestamps                                   | matchings  | code |
+        | abbecd   | 10 11 27 1516914902 1516914913 1516914952    | ab,ecd     | Ok   |
+

include/engine/api/match_parameters_tidy.hpp

@@ -48,12 +48,14 @@ inline Result keep_all(const MatchParameters &params)
 
     result.can_be_removed.resize(params.coordinates.size(), false);
     result.was_waypoint.resize(params.coordinates.size(), true);
+    // by default all input coordinates are treated as waypoints
     if (!params.waypoints.empty())
     {
         for (const auto p : params.waypoints)
         {
             result.was_waypoint.set(p, false);
         }
+        // logic is a little funny, uses inversion to set the bitfield
         result.was_waypoint.flip();
     }
     result.tidied_to_original.reserve(params.coordinates.size());

src/engine/plugins/match.cpp

@@ -247,6 +247,7 @@ Status MatchPlugin::HandleRequest(const RoutingAlgorithmsInterface &algorithms,
     }
 
     // Error: Check if user-supplied waypoints can be found in the resulting matches
+    if (!parameters.waypoints.empty())
     {
         std::set<std::size_t> tidied_waypoints(tidied.parameters.waypoints.begin(),
                                                tidied.parameters.waypoints.end());
@@ -262,6 +263,9 @@ Status MatchPlugin::HandleRequest(const RoutingAlgorithmsInterface &algorithms,
                 "NoMatch", "Requested waypoint parameter could not be matched.", json_result);
         }
     }
+    // we haven't errored yet, only allow leg collapsing if it was originally requested
+    BOOST_ASSERT(parameters.waypoints.empty() || sub_matchings.size() == 1);
+    const auto collapse_legs = !parameters.waypoints.empty();
 
     // each sub_route will correspond to a MatchObject
     std::vector<InternalRouteResult> sub_routes(sub_matchings.size());
@@ -286,7 +290,7 @@ Status MatchPlugin::HandleRequest(const RoutingAlgorithmsInterface &algorithms,
         sub_routes[index] =
             algorithms.ShortestPathSearch(sub_routes[index].segment_end_coordinates, {false});
         BOOST_ASSERT(sub_routes[index].shortest_path_weight != INVALID_EDGE_WEIGHT);
-        if (!tidied.parameters.waypoints.empty())
+        if (collapse_legs)
         {
             std::vector<bool> waypoint_legs;
             waypoint_legs.reserve(sub_matchings[index].indices.size());