Thrown soap/banana/(etc?) will fail to slip until it lands

Content.Shared/Slippery/SlipperySystem.cs

@@ -1,9 +1,12 @@
 using Content.Shared.Administration.Logs;
 using Content.Shared.Database;
 using Content.Shared.Inventory;
+using Robust.Shared.Network;
+using Content.Shared.Popups;
 using Content.Shared.StatusEffect;
 using Content.Shared.StepTrigger.Systems;
 using Content.Shared.Stunnable;
+using Content.Shared.Throwing;
 using JetBrains.Annotations;
 using Robust.Shared.Audio.Systems;
 using Robust.Shared.Containers;
@@ -18,6 +21,8 @@ public sealed class SlipperySystem : EntitySystem
 {
     [Dependency] private readonly ISharedAdminLogManager _adminLogger = default!;
     [Dependency] private readonly SharedAudioSystem _audio = default!;
+    [Dependency] private readonly INetManager _netManager = default!;
+    [Dependency] private readonly SharedPopupSystem _popup = default!;
     [Dependency] private readonly SharedStunSystem _stun = default!;
     [Dependency] private readonly StatusEffectsSystem _statusEffects = default!;
     [Dependency] private readonly SharedContainerSystem _container = default!;
@@ -30,6 +35,7 @@ public override void Initialize()
         SubscribeLocalEvent<SlipperyComponent, StepTriggerAttemptEvent>(HandleAttemptCollide);
         SubscribeLocalEvent<SlipperyComponent, StepTriggeredEvent>(HandleStepTrigger);
         SubscribeLocalEvent<NoSlipComponent, SlipAttemptEvent>(OnNoSlipAttempt);
+        SubscribeLocalEvent<ThrownItemComponent, SlipCausingAttemptEvent>(OnThrownSlipAttempt);
         // as long as slip-resistant mice are never added, this should be fine (otherwise a mouse-hat will transfer it's power to the wearer).
         SubscribeLocalEvent<NoSlipComponent, InventoryRelayedEvent<SlipAttemptEvent>>((e, c, ev) => OnNoSlipAttempt(e, c, ev.Args));
     }
@@ -52,6 +58,16 @@ private static void OnNoSlipAttempt(EntityUid uid, NoSlipComponent component, Sl
         args.Cancel();
     }
 
+    private void OnThrownSlipAttempt(EntityUid uid, ThrownItemComponent comp, ref SlipCausingAttemptEvent args)
+    {
+        args.Cancelled = true;
+
+        //TODO: If it's after 2024 April and this popup is still here, remove it
+        // Only here so people who don't read even the changelog won't think soap suddenly broke
+        if (_netManager.IsServer)
+            _popup.PopupEntity(Loc.GetString("thrown-slippery-missed"), uid, PopupType.Medium);
+    }
+
     private bool CanSlip(EntityUid uid, EntityUid toSlip)
     {
         return !_container.IsEntityInContainer(uid)
@@ -68,6 +84,11 @@ private void TrySlip(EntityUid uid, SlipperyComponent component, EntityUid other
         if (attemptEv.Cancelled)
             return;
 
+        var attemptCausingEv = new SlipCausingAttemptEvent();
+        RaiseLocalEvent(uid, ref attemptCausingEv);
+        if (attemptCausingEv.Cancelled)
+            return;
+
         var ev = new SlipEvent(other);
         RaiseLocalEvent(uid, ref ev);
 
@@ -107,7 +128,13 @@ public sealed class SlipAttemptEvent : CancellableEntityEventArgs, IInventoryRel
 }
 
 /// <summary>
-///     This event is raised directed at an entity that CAUSED some other entity to slip (e.g., the banana peel).
+/// Raised on an entity that is causing the slip event (e.g, the banana peel), to determine if the slip attempt should be cancelled.
 /// </summary>
+/// <param name="Cancelled">If the slip should be cancelled</param>
+[ByRefEvent]
+public record struct SlipCausingAttemptEvent (bool Cancelled);
+
+/// Raised on an entity that CAUSED some other entity to slip (e.g., the banana peel).
+/// <param name="Slipped">The entity being slipped</param>
 [ByRefEvent]
 public readonly record struct SlipEvent(EntityUid Slipped);

Resources/Locale/en-US/movement/slipping.ftl

@@ -0,0 +1 @@
+thrown-slippery-missed = MISS