Make pushing a toggle (#4330)

* Make pushing a toggle

* Review

Content.Shared/CCVar/CCVars.cs

@@ -181,6 +181,15 @@ namespace Content.Shared.CCVar
         public static readonly CVarDef<float> StopSpeed =
             CVarDef.Create("physics.stop_speed", 0.1f);
 
+        /// <summary>
+        /// Whether mobs can push objects like lockers.
+        /// </summary>
+        /// <remarks>
+        /// Technically client doesn't need to know about it but this may prevent a bug in the distant future so it stays.
+        /// </remarks>
+        public static readonly CVarDef<bool> MobPushing =
+            CVarDef.Create("physics.mob_pushing", true, CVar.REPLICATED);
+
         /*
          * Ambience
          */

Content.Shared/Movement/EntitySystems/SharedMobMoverSystem.cs

@@ -1,23 +1,34 @@
+using Content.Shared.CCVar;
 using Content.Shared.Movement.Components;
+using Robust.Shared.Configuration;
 using Robust.Shared.GameObjects;
+using Robust.Shared.IoC;
 using Robust.Shared.Maths;
 using Robust.Shared.Physics;
-using Robust.Shared.Physics.Collision;
 using Robust.Shared.Physics.Dynamics;
 
 namespace Content.Shared.Movement.EntitySystems
 {
     public sealed class SharedMobMoverSystem : EntitySystem
     {
+        private bool _pushingEnabled;
+
         public override void Initialize()
         {
             base.Initialize();
             Get<SharedPhysicsSystem>().KinematicControllerCollision += HandleCollisionMessage;
+            IoCManager.Resolve<IConfigurationManager>().OnValueChanged(CCVars.MobPushing, SetPushing, true);
+        }
+
+        private void SetPushing(bool value)
+        {
+            _pushingEnabled = value;
         }
 
         public override void Shutdown()
         {
             base.Shutdown();
+            IoCManager.Resolve<IConfigurationManager>().UnsubValueChanged(CCVars.MobPushing, SetPushing);
             Get<SharedPhysicsSystem>().KinematicControllerCollision -= HandleCollisionMessage;
         }
 
@@ -26,6 +37,8 @@ namespace Content.Shared.Movement.EntitySystems
         /// </summary>
         private void HandleCollisionMessage(Fixture ourFixture, Fixture otherFixture, float frameTime, Vector2 worldNormal)
         {
+            if (!_pushingEnabled) return;
+
             var otherBody = otherFixture.Body;
 
             if (otherBody.BodyType != BodyType.Dynamic || !otherFixture.Hard) return;