FIX: ISXB-953 InputSystemProvider GC Alloc (#1973)

* Fixed isxb-953. Avoided memory allocation in InputSystemProvider.Update.

* Updated Changelog with fix for isxb-953.

* Added unit test for isxb-953.

Author: benoitalain

Assets/Tests/InputSystem/Plugins/InputForUITests.cs

@@ -8,6 +8,8 @@
 using UnityEngine.InputSystem;
 using UnityEngine.InputSystem.Controls;
 using UnityEngine.InputSystem.LowLevel;
+using UnityEngine.TestTools;
+using UnityEngine.TestTools.Constraints;
 #if UNITY_EDITOR
 using UnityEditor;
 using UnityEngine.InputSystem.Editor;
@@ -16,6 +18,7 @@
 using UnityEngine.TestTools;
 using Event = UnityEngine.InputForUI.Event;
 using EventProvider = UnityEngine.InputForUI.EventProvider;
+using Is = NUnit.Framework.Is;
 
 // Note that these tests do not verify InputForUI default bindings at all.
 // It only verifies integration with Project-wide Input Actions.
@@ -682,6 +685,13 @@ public void ActionWithDifferentExpectedControlType_ShouldGenerateWarning(string
 
 #endif // UNITY_EDITOR
 
+    [Test]
+    public void Update_DoesntAllocate()
+    {
+        Update(); // Warm-up internals
+        Assert.That(Update, Is.Not.AllocatingGCMemory());
+    }
+
     static void Update()
     {
         EventProvider.NotifyUpdate();

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -10,6 +10,9 @@ however, it has to be formatted properly to pass verification tests.
 
 ## [Unreleased] - yyyy-mm-dd
 
+### Fixed
+- Fixed memory allocation on every frame when using UIDocument without EventSystem. [ISXB-953](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-953)
+
 ### Changed
 - Use `ProfilerMarker` instead of `Profiler.BeginSample` and `Profiler.EndSample` when appropriate to enable recording of profiling data.
 

Packages/com.unity.inputsystem/InputSystem/Plugins/InputForUI/InputSystemProvider.cs

@@ -127,7 +127,7 @@ public void Update()
             // This is necessary to ensure that events are dispatched in the correct order.
             // If all events are of the PointerEvents type, sorting is based on reverse order of the EventSource enum.
             // Touch -> Pen -> Mouse.
-            m_Events.Sort(SortEvents);
+            m_Events.Sort((a, b) => SortEvents(a, b));
 
             var currentTime = (DiscreteTime)Time.timeAsRational;