Reposition: tolerate more scenarios in ATC_mgr

When starting at an airport, but not at parking or a runway, create
an empty AIFlightPlan, and ensure the AIManager code doesn’t choke on
empty FPs.

Add a unit-test which simulates the C172 tutorial reposition logic,
which is a little gnarly.

src/AIModel/AIAircraft.cxx

@@ -1022,7 +1022,7 @@ void FGAIAircraft::controlSpeed(FGAIWaypoint* curr, FGAIWaypoint* next) {
  * Update target values (heading, alt, speed) depending on flight plan or control properties
  */
 void FGAIAircraft::updatePrimaryTargetValues(double dt, bool& flightplanActive, bool& aiOutOfSight) {
-    if (fp)                      // AI object has a flightplan
+    if (fp && fp->isValidPlan()) // AI object has a flightplan
     {
         //TODO make this a function of AIBase
         time_t now = globals->get_time_params()->get_cur_time();

src/AIModel/AIFlightPlan.cxx

@@ -327,12 +327,15 @@ FGAIWaypoint* FGAIFlightPlan::getLastWaypoint()
 
 FGAIWaypoint* FGAIFlightPlan::getPreviousWaypoint( void ) const
 {
-  if (wpt_iterator == waypoints.begin()) {
-      return nullptr;
-  } else {
-    wpt_vector_iterator prev = wpt_iterator;
-    return *(--prev);
-  }
+    if (empty())
+        return nullptr;
+
+    if (wpt_iterator == waypoints.begin()) {
+        return nullptr;
+    } else {
+        wpt_vector_iterator prev = wpt_iterator;
+        return *(--prev);
+    }
 }
 
 FGAIWaypoint* FGAIFlightPlan::getCurrentWaypoint( void ) const
@@ -357,6 +360,9 @@ FGAIWaypoint* FGAIFlightPlan::getNextWaypoint( void ) const
 
 void FGAIFlightPlan::IncrementWaypoint(bool eraseWaypoints )
 {
+    if (empty())
+        return;
+
     if (eraseWaypoints)
     {
         if (wpt_iterator == waypoints.begin())
@@ -376,11 +382,17 @@ void FGAIFlightPlan::IncrementWaypoint(bool eraseWaypoints )
 
 void FGAIFlightPlan::DecrementWaypoint()
 {
-  wpt_iterator--;
+    if (empty())
+        return;
+
+    wpt_iterator--;
 }
 
 void FGAIFlightPlan::eraseLastWaypoint()
 {
+    if (empty())
+        return;
+
     delete (waypoints.back());
     waypoints.pop_back();;
     wpt_iterator = waypoints.begin();
@@ -559,3 +571,15 @@ FGAirportRef FGAIFlightPlan::arrivalAirport() const
 {
     return arrival;
 }
+
+FGAIFlightPlan* FGAIFlightPlan::createDummyUserPlan()
+{
+    FGAIFlightPlan* fp = new FGAIFlightPlan;
+    fp->isValid = false;
+    return fp;
+}
+
+bool FGAIFlightPlan::empty() const
+{
+    return waypoints.empty();
+}

src/AIModel/AIFlightPlan.hxx

@@ -150,6 +150,12 @@ public:
    ~FGAIFlightPlan();
 
    /**
+        @brief create a neatrly empty FlightPlan for the user aircraft, based
+     on the current position and route-manager data.
+     */
+   static FGAIFlightPlan* createDummyUserPlan();
+   /**
+    
      @brief read a flight-plan from a file.
      All current contents of the flight-plan are replaxced, and the current waypoint is reset to the beginning
      */
@@ -220,6 +226,9 @@ public:
 
     FGAirportRef departureAirport() const;
     FGAirportRef arrivalAirport() const;
+
+    bool empty() const;
+
 private:
   FGAIFlightPlan *sid;
   typedef std::vector <FGAIWaypoint*> wpt_vector_type;

src/ATC/atc_mgr.cxx

@@ -191,19 +191,20 @@ void FGATCManager::postinit()
             userAircraft->setTakeOffStatus(2);
         } else {
             // We're on the ground somewhere. Handle this case later.
-            
+
             // important : we are on the ground, so reset the AIFlightPlan back to
-            // an empty one. Otherwise, in the reposition case, we end up with a
+            // a dummy one. Otherwise, in the reposition case, we end up with a
             // stale flight-plan which confuses other code (eg, PositionInit::finalizeForParking)
             // see unit test: PosInitTests::testRepositionAtOccupied
+            fp.reset(FGAIFlightPlan::createDummyUserPlan());
             userAircraft->FGAIBase::setFlightPlan(std::move(fp));
             controller = nullptr;
             
             initSucceeded = true; // should be false?
             return;
         }
-        
-        if (fp) {
+
+        if (fp && !fp->empty()) {
             fp->getLastWaypoint()->setName( fp->getLastWaypoint()->getName() + string("legend"));
         }
      } else {
@@ -222,7 +223,9 @@ void FGATCManager::postinit()
     
     if (controller) {
         FGAIFlightPlan* plan = userAircraft->GetFlightPlan();
-        controller->announcePosition(userAircraft->getID(), plan, plan->getCurrentWaypoint()->getRouteIndex(),
+        const int routeIndex = (plan && plan->getCurrentWaypoint()) ? plan->getCurrentWaypoint()->getRouteIndex() : 0;
+        controller->announcePosition(userAircraft->getID(), plan,
+                                     routeIndex,
                                      userAircraft->_getLatitude(),
                                      userAircraft->_getLongitude(),
                                      userAircraft->_getHeading(),
@@ -319,7 +322,6 @@ void FGATCManager::update ( double time ) {
         // user should be able to select a new route, but for now just shut down the
         // system. 
         if (size < 3) {
-            SG_LOG(SG_ATC, SG_INFO, "Shutting down the atc_mgr - ran out of waypoints");
             return;
         }
 #if 0

src/Main/positioninit.cxx

@@ -600,6 +600,10 @@ bool initPosition()
 
   bool set_pos = false;
 
+  // clear this value, so we don't preserve an old value and confuse
+  // the ATC manager. We will set it again if it's valid
+  fgSetString("/sim/atc/runway", "");
+
   // If glideslope is specified, then calculate offset-distance or
   // altitude relative to glide slope if either of those was not
   // specified.
@@ -683,9 +687,6 @@ bool initPosition()
     // until position finalisation
     // the rest of the work happens in finalizePosFromParkpos
     if ( airportParkingSetVicinity( apt ) ) {
-      // set tower position
-      fgSetString("/sim/airport/closest-airport-id",  apt.c_str());
-      fgSetString("/sim/tower/airport-id",  apt.c_str());
       set_pos = true;
     }
   }
@@ -693,10 +694,6 @@ bool initPosition()
   if ( !set_pos && !apt.empty() && !rwy_no.empty() ) {
     // An airport + runway is requested
     if ( fgSetPosFromAirportIDandRwy( apt, rwy_no, rwy_req ) ) {
-      // set tower position (a little off the heading for single
-      // runway airports)
-      fgSetString("/sim/airport/closest-airport-id",  apt.c_str());
-      fgSetString("/sim/tower/airport-id",  apt.c_str());
       set_pos = true;
     }
   }
@@ -704,14 +701,18 @@ bool initPosition()
   if ( !set_pos && !apt.empty() ) {
     // An airport is requested (find runway closest to hdg)
     if ( setPosFromAirportIDandHdg( apt, hdg ) ) {
-      // set tower position (a little off the heading for single
-      // runway airports)
-      fgSetString("/sim/airport/closest-airport-id",  apt.c_str());
-      fgSetString("/sim/tower/airport-id",  apt.c_str());
       set_pos = true;
     }
   }
 
+  // if an airport ID was requested, set closest-airport-id
+  // and tower based upon it.
+  if (!apt.empty() && set_pos) {
+      // set tower position
+      fgSetString("/sim/airport/closest-airport-id", apt.c_str());
+      fgSetString("/sim/tower/airport-id", apt.c_str());
+  }
+
   if (original_hdg < 9990.0) {
     // The user-set heading may be overridden by the setPosFromAirportID above.
     SG_LOG(SG_GENERAL, SG_ALERT, "Setting heading preset to  : " << original_hdg);

test_suite/unit_tests/Main/test_posinit.cxx

@@ -177,10 +177,6 @@ void PosInitTests::testAirportAltitudeOffsetStartup()
 
     CPPUNIT_ASSERT(fgGetBool("/sim/presets/airport-requested"));
     initPosition();
-    
-    
-    
-    initPosition();
 
     SGGeod expectedPos = SGGeodesy::direct(FGAirport::getByIdent("EDDF")->geod(), 270, 5 * SG_NM_TO_METER);
     checkPosition(expectedPos, 5000.0);
@@ -616,6 +612,53 @@ void PosInitTests::testAirportRepositionAirport()
    
 }
 
+// this simulates what the C172 preflight tutorial does,
+// where the user is likely at a random airport (on a runway), and starts
+// the preflight tutorial, which repositions them to a ramp location
+// at PHTO
+void PosInitTests::testAirportRunwayRepositionAirport()
+{
+    {
+        Options* opts = Options::sharedInstance();
+        opts->setShouldLoadDefaultConfig(false);
+        const char* args[] = {"dummypath", "--airport=EDDS", "--runway=07"};
+        opts->init(3, (char**)args, SGPath());
+        opts->processOptions();
+    }
+
+    CPPUNIT_ASSERT(fgGetBool("/sim/presets/airport-requested"));
+    CPPUNIT_ASSERT(fgGetBool("/sim/presets/runway-requested"));
+    checkRunway(std::string("07"));
+    initPosition();
+    simulateFinalizePosition();
+
+    checkClosestAirport(std::string("EDDS"));
+    checkPosition(FGAirport::getByIdent("EDDS")->geod(), 10000.0);
+
+    // Now re-position to PHTO runway
+    // Reset the Lat/Lon as these will be used in preference to the airport ID
+    fgSetDouble("/sim/presets/longitude-deg", -155.0597483);
+    fgSetDouble("/sim/presets/latitude-deg", 19.71731272);
+    fgSetString("/sim/presets/airport-id", "PHTO");
+    fgSetDouble("/sim/presets/heading-deg", 125);
+    fgSetBool("/sim/presets/on-ground", true);
+    fgSetBool("/sim/presets/runway-requested", true);
+    fgSetBool("/sim/presets/airport-requested", true);
+    fgSetBool("/sim/presets/parking-requested", true);
+
+    simulateStartReposition();
+    finalizePosition();
+
+    FGTestApi::runForTime(1.0);
+
+    checkClosestAirport(std::string("PHTO"));
+    checkPosition(FGAirport::getByIdent("PHTO")->geod(), 5000.0);
+    checkHeading(125);
+    checkOnGround();
+
+    FGTestApi::runForTime(1.0);
+}
+
 void PosInitTests::testParkInvalid()
 {
     {

test_suite/unit_tests/Main/test_posinit.hxx

@@ -46,8 +46,9 @@ class PosInitTests : public CppUnit::TestFixture
     CPPUNIT_TEST(testRepositionAtParking);
     CPPUNIT_TEST(testParkAtOccupied);
     CPPUNIT_TEST(testParkInvalid);
-    
-    
+    CPPUNIT_TEST(testAirportRunwayRepositionAirport);
+
+
     // Navaid tests
     CPPUNIT_TEST(testVOROnlyStartup);
     CPPUNIT_TEST(testVOROffsetAltitudeHeadingStartup);
@@ -116,6 +117,8 @@ public:
     void testRepositionAtSameParking();
     void testRepositionAtOccupied();
     void testRepositionAtInvalid();
+    void testAirportRunwayRepositionAirport();
+
 private:
     // Helper functions for tests.  Return void as they use CPPUNIT_ASSERT
     void checkAlt(float value);