Player snaps back if teleport fails

src/game.cpp

@@ -11377,8 +11377,13 @@ point game::place_player( const tripoint &dest_loc, bool quick )
     return submap_shift;
 }
 
-void game::place_player_overmap( const tripoint_abs_omt &om_dest, bool move_player )
+void game::place_player_overmap( const tripoint_abs_ms &ms_dest, bool move_player )
 {
+    if( ms_dest == project_to<coords::ms>( u.global_sm_location() - point( HALF_MAPSIZE,
+                                           HALF_MAPSIZE ) ) + u.pos() ) {
+        return; // Already there
+    }
+
     // if player is teleporting around, they don't bring their horse with them
     if( u.is_mounted() ) {
         u.remove_effect( effect_riding );
@@ -11399,20 +11404,50 @@ void game::place_player_overmap( const tripoint_abs_omt &om_dest, bool move_play
     m.rebuild_vehicle_level_caches();
     m.access_cache( m.get_abs_sub().z() ).map_memory_cache_dec.reset();
     m.access_cache( m.get_abs_sub().z() ).map_memory_cache_ter.reset();
-    // offset because load_map expects the coordinates of the top left corner, but the
-    // player will be centered in the middle of the map.
+    // Set this now, if game::place_player fails we'll need it to recover.
+    const tripoint_abs_sm tele_from = u.global_sm_location();
+    // The subtraction is to get the reality bubble NW corner from the center position.
     const tripoint_abs_sm map_sm_pos =
-        project_to<coords::sm>( om_dest ) - point( HALF_MAPSIZE, HALF_MAPSIZE );
-    const tripoint player_pos( u.pos().xy(), map_sm_pos.z() );
+        project_to<coords::sm>( ms_dest ) - point( HALF_MAPSIZE, HALF_MAPSIZE );
+    const tripoint_bub_ms player_pos( u.pos_bub().xy(), map_sm_pos.z() );
     load_map( map_sm_pos );
     load_npcs();
     m.spawn_monsters( true ); // Static monsters
     update_overmap_seen();
     // update weather now as it could be different on the new location
     weather.nextweather = calendar::turn;
     if( move_player ) {
-        place_player( player_pos );
+        place_player( player_pos.raw() );
+    }
+    const tripoint_abs_sm tele_to = u.global_sm_location();
+    if( tele_from != tele_to || !move_player ) {
+        return;
+    } // else tele_from == tele_to !!!
+    // We've failed to teleport for some reason (probably monsters occupying destination squares).
+    // Let's try to recover gracefully. But also throw a warning, this is bad!
+    debugmsg( "Failed to place player at destination.  If you see this outside of debug teleporting it is a bug." );
+    update_map( u, ms_dest.z() != tele_from.z() );
+    // This recursive call safely calls map::load_map() again after making sure everything has been unloaded properly.
+    // Basically, its only purpose it to reset the z-level to the z-level you teleported *from*. Otherwise, it's redundant after update_map
+    // Again, translate the reality bubble reference to a mapsquare one.
+    place_player_overmap( project_to<coords::ms>( tele_from - point( HALF_MAPSIZE,
+                          HALF_MAPSIZE ) ) + player_pos.raw() );
+}
+
+void game::place_player_overmap( const tripoint_abs_omt &om_dest, bool move_player )
+{
+    // Project the bubble reference to a submap reference.
+    tripoint offset = u.pos() - point( 5 * SEEX, 5 * SEEY );
+
+    // And then on to an overmap one.
+    if( abs( u.global_sm_location().x() ) % 2 == 1 ) {
+        offset.x += SEEX;
+    }
+    if( abs( u.global_sm_location().y() ) % 2 == 1 ) {
+        offset.y += SEEY;
     }
+
+    place_player_overmap( project_to<coords::ms>( om_dest ) + offset, move_player );
 }
 
 bool game::phasing_move( const tripoint &dest_loc, const bool via_ramp )

src/game.h

@@ -853,7 +853,7 @@
         // at all and they will prevent the door from closing.
         // If bash_dmg is smaller than 0, _every_ item on the door tile will
         // prevent the door from closing. If bash_dmg is 0, only very small items
         // will do so, if bash_dmg is greater than 0, items won't stop the door
         // from closing at all.
         // If the door gets closed the items on the door tile get moved away or destroyed.
         // TODO: Get rid of untyped overload.
@@ -948,6 +948,7 @@
         void insert_item( drop_locations &targets );
         // Places the player at the specified point; hurts feet, lists items etc.
         point place_player( const tripoint &dest, bool quick = false );
+        void place_player_overmap( const tripoint_abs_ms &ms_dest, bool move_player = true );
         void place_player_overmap( const tripoint_abs_omt &om_dest, bool move_player = true );
         void perhaps_add_random_npc( bool ignore_spawn_timers_and_rates );
         static void display_om_pathfinding_progress( size_t open_set, size_t known_size );

tests/water_movement_test.cpp

@@ -118,7 +118,7 @@
 
     GIVEN( "avatar is underwater at z-2" ) {
         dummy.set_underwater( true );
-        dummy.setpos( test_origin + tripoint( 0, 0, -2 ) );
+        dummy.setpos( test_origin );
         g->vertical_shift( -2 );
 
         WHEN( "avatar dives down" ) {
@@ -261,8 +261,14 @@
 static int swimming_steps( avatar &swimmer )
 {
     map &here = get_map();
+    // This shouldn't work.
+    CAPTURE( swimmer.pos() );
+    avatar_action::move( swimmer, here, swimmer.pos() + tripoint_west );
+    CAPTURE( swimmer.pos() );
     const tripoint left = swimmer.pos();
     const tripoint right = left + tripoint_east;
+    CAPTURE( left );
+    CAPTURE( right );
     int steps = 0;
     constexpr int STOP_STEPS = 9000;
     int last_moves = swimmer.get_speed();
@@ -272,10 +278,10 @@
     while( swimmer.get_stamina() > 0 && !swimmer.has_effect( effect_winded ) && steps < STOP_STEPS ) {
         if( steps % 2 == 0 ) {
             REQUIRE( swimmer.pos() == left );
-            REQUIRE( avatar_action::move( swimmer, here, tripoint_east ) );
+            REQUIRE( avatar_action::move( swimmer, here, right ) );
         } else {
             REQUIRE( swimmer.pos() == right );
-            REQUIRE( avatar_action::move( swimmer, here, tripoint_west ) );
+            REQUIRE( avatar_action::move( swimmer, here, left ) );
         }
         ++steps;
         REQUIRE( swimmer.get_moves() < last_moves );
@@ -905,6 +911,7 @@
 
 TEST_CASE( "check_swim_move_cost_and_distance_values", "[swimming][slow]" )
 {
+    clear_avatar();
     setup_test_lake();
 
     avatar &dummy = get_avatar();