From de8dcb75bfef334b3f49f97441556f2999c5729a Mon Sep 17 00:00:00 2001
From: Leon Friedrich <60421075+ElectroJr@users.noreply.github.com>
Date: Wed, 23 Feb 2022 17:58:06 +1300
Subject: [PATCH] Fix interact using sometimes having target==used (#6847)

---
 Content.Shared/Interaction/IInteractUsing.cs          | 6 ++++++
 Content.Shared/Interaction/SharedInteractionSystem.cs | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/Content.Shared/Interaction/IInteractUsing.cs b/Content.Shared/Interaction/IInteractUsing.cs
index 04f1e6c003..5a639e27ab 100644
--- a/Content.Shared/Interaction/IInteractUsing.cs
+++ b/Content.Shared/Interaction/IInteractUsing.cs
@@ -4,6 +4,7 @@ using JetBrains.Annotations;
 using Robust.Shared.Analyzers;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Map;
+using Robust.Shared.Utility;
 
 namespace Content.Shared.Interaction
 {
@@ -78,6 +79,11 @@ namespace Content.Shared.Interaction
 
         public InteractUsingEvent(EntityUid user, EntityUid used, EntityUid target, EntityCoordinates clickLocation, bool predicted = false)
         {
+            // Interact using should not have the same used and target.
+            // That should be a use-in-hand event instead.
+            // If this is not the case, can lead to bugs (e.g., attempting to merge a item stack into itself).
+            DebugTools.Assert(used != target);
+
             User = user;
             Used = used;
             Target = target;
diff --git a/Content.Shared/Interaction/SharedInteractionSystem.cs b/Content.Shared/Interaction/SharedInteractionSystem.cs
index 8874b7cc0c..253b77b6f3 100644
--- a/Content.Shared/Interaction/SharedInteractionSystem.cs
+++ b/Content.Shared/Interaction/SharedInteractionSystem.cs
@@ -216,6 +216,12 @@ namespace Content.Shared.Interaction
             if (checkCanUse && !_actionBlockerSystem.CanUseHeldEntity(user))
                 return;
 
+            if (target == hand.HeldEntity)
+            {
+                UseInHandInteraction(user, target.Value, checkCanUse: false, checkCanInteract: false);
+                return;
+            }
+
             if (inRangeUnobstructed && target != null)
             {
                 InteractUsing(