Pets follow stairs well

src/game.cpp

@@ -227,6 +227,7 @@ static const efftype_id effect_downed( "downed" );
 static const efftype_id effect_fake_common_cold( "fake_common_cold" );
 static const efftype_id effect_fake_flu( "fake_flu" );
 static const efftype_id effect_laserlocked( "laserlocked" );
+static const efftype_id effect_led_by_leash( "led_by_leash" );
 static const efftype_id effect_no_sight( "no_sight" );
 static const efftype_id effect_onfire( "onfire" );
 static const efftype_id effect_pet( "pet" );
@@ -11954,8 +11955,8 @@ void game::vertical_move( int movez, bool force, bool peeking )
             // TODO: just check if it's going for the avatar's location, it's simpler
             Creature *target = critter.attack_target();
             if( ( target && target->is_avatar() ) || ( !critter.has_effect( effect_ridden ) &&
-                    critter.has_effect( effect_pet ) && critter.friendly == -1 &&
-                    !critter.has_effect( effect_tied ) ) ) {
+                ( critter.is_pet_follow() || critter.has_effect( effect_led_by_leash ) ) &&
+                !critter.has_effect( effect_tied ) && critter.sees( u ) ) ) {
                 monsters_following.push_back( &critter );
             }
         }

src/monexamine.cpp

@@ -456,6 +456,7 @@ void start_leading( monster &z )
         untie_pet( z );
     }
     z.add_effect( effect_led_by_leash, 1_turns, true );
+    z.unset_dest();
     add_msg( _( "You take hold of the %s's leash to make it follow you." ), z.get_name() );
 }
 

src/monmove.cpp

@@ -758,28 +758,24 @@ void monster::plan()
             next_stop = patrol_route.at( next_patrol_point );
         }
         set_dest( next_stop );
-    } else if( friendly != 0 && has_effect( effect_led_by_leash ) ) {
+    } else if( friendly != 0 && has_effect( effect_led_by_leash ) &&
+            get_location().z() == get_dest().z() ) {
         // visibility doesn't matter, we're getting pulled by a leash
-        if( rl_dist( get_location(), player_character.get_location() ) > 1 ) {
-            set_dest( player_character.get_location() );
-        } else {
-            unset_dest();
-        }
+        // To use stairs smoothly, if the destination is on a different Z-level, move there first.
+        set_dest( player_character.get_location() );
         if( friendly > 0 && one_in( 3 ) ) {
             // Grow restless with no targets
             friendly--;
         }
     } else if( friendly > 0 && one_in( 3 ) ) {
         // Grow restless with no targets
         friendly--;
-    } else if( friendly < 0 && sees( player_character ) &&
-               // Simpleminded animals are too dumb to follow the player.
-               !has_flag( mon_flag_PET_WONT_FOLLOW ) ) {
-        if( rl_dist( get_location(), player_character.get_location() ) > 2 ) {
-            set_dest( player_character.get_location() );
-        } else {
-            unset_dest();
-        }
+    } else if( is_pet_follow() && sees( player_character ) &&
+            ( get_location().z() == player_character.get_location().z() ||
+            get_location().z() == get_dest().z() ) ) {
+        // Simpleminded animals are too dumb to follow the player.
+        // To use stairs smoothly, if the destination is on a different Z-level, move there first.
+        set_dest( player_character.get_location() );
     }
 }
 
@@ -977,7 +973,15 @@ void monster::move()
         }
     }
 
-    if( ( current_attitude == MATT_IGNORE && patrol_route.empty() ) ||
+    if( is_pet_follow() || ( friendly != 0 && has_effect( effect_led_by_leash ) ) ) {
+        const int dist = rl_dist( get_location(), get_dest() );
+        if( ( dist <= 1 || ( dist <= 2 && !has_effect( effect_led_by_leash ) && sees( player_character ) ) ) &&
+            ( get_dest() == player_character.get_location() && get_location().z() == player_character.get_location().z() ) ) {
+            moves = 0;
+            stumble();
+            return;
+        }
+    } else if( ( current_attitude == MATT_IGNORE && patrol_route.empty() ) ||
         ( ( current_attitude == MATT_FOLLOW ||
             ( has_flag( mon_flag_KEEP_DISTANCE ) && !( current_attitude == MATT_FLEE ) ) )
           && rl_dist( get_location(), get_dest() ) <= type->tracking_distance ) ) {

src/monster.cpp

@@ -104,6 +104,7 @@ static const efftype_id effect_no_sight( "no_sight" );
 static const efftype_id effect_onfire( "onfire" );
 static const efftype_id effect_pacified( "pacified" );
 static const efftype_id effect_paralyzepoison( "paralyzepoison" );
+static const efftype_id effect_pet( "pet" );
 static const efftype_id effect_photophobia( "photophobia" );
 static const efftype_id effect_poison( "poison" );
 static const efftype_id effect_ridden( "ridden" );
@@ -177,6 +178,7 @@ static const mon_flag_str_id mon_flag_NO_BREED( "NO_BREED" );
 static const mon_flag_str_id mon_flag_NO_FUNG_DMG( "NO_FUNG_DMG" );
 static const mon_flag_str_id mon_flag_PARALYZEVENOM( "PARALYZEVENOM" );
 static const mon_flag_str_id mon_flag_PET_MOUNTABLE( "PET_MOUNTABLE" );
+static const mon_flag_str_id mon_flag_PET_WONT_FOLLOW( "PET_WONT_FOLLOW" );
 static const mon_flag_str_id mon_flag_PHOTOPHOBIC( "PHOTOPHOBIC" );
 static const mon_flag_str_id mon_flag_PLASTIC( "PLASTIC" );
 static const mon_flag_str_id mon_flag_QUEEN( "QUEEN" );
@@ -1283,6 +1285,16 @@ bool monster::made_of( phase_id p ) const
     return type->phase == p;
 }
 
+bool monster::is_pet() const
+{
+    return friendly == -1 && has_effect( effect_pet );
+}
+
+bool monster::is_pet_follow() const
+{
+    return is_pet() && !has_flag( mon_flag_PET_WONT_FOLLOW );
+}
+
 std::vector<material_id> monster::get_absorb_material() const
 {
     return type->absorb_material;

src/monster.h

@@ -181,6 +181,8 @@ class monster : public Creature
         bool made_of( phase_id p ) const; // Returns true if its phase is p
 
         bool shearable() const;
+        bool is_pet() const;
+        bool is_pet_follow() const;
 
         bool avoid_trap( const tripoint &pos, const trap &tr ) const override;