CHANGE: Override UGUI EventSystem with InputSystemUIInputModule (#1902)

* Override InputModule component of EventSystem

* Make it override only when ISX is enabled and IM disabled

InputSystem should override the input module for the `EventSystem` game object only when it's the only input system available. If IM (Input Manager) is available as well or is the only input backend available, we fallback to default behavior of adding `StandaloneInputModule`.

* Use static ObjectFactory.AddComponent

* Test that UGUI EventSystem is created correctly

This test assumes that the Input System package is enabled in the
project. In cases like this, the EventSystem GameObject will always
be created with the InputSystemUIInputModule.

* Rely on ENABLE_INPUT_SYSTEM instead

This avoids us having to use `EditorPlayerSettingsHelpers` which uses `FindObjectsOfTypeAll`. This is not allowed to be done on ScriptableObject constructor (or instance field initializer)

* Update CHANGELOG

---------

Co-authored-by: Lyndon Homewood <33493311+lyndon-unity@users.noreply.github.com>

Author: jfreire-unity

Assets/Tests/InputSystem.Editor/UGUITests.cs

@@ -0,0 +1,50 @@
+#if UNITY_EDITOR && UNITY_6000_0_OR_NEWER
+using System;
+using NUnit.Framework;
+using UnityEditor;
+using UnityEditor.SceneManagement;
+using UnityEngine.SceneManagement;
+using UnityEngine;
+using UnityEngine.EventSystems;
+using UnityEngine.InputSystem.UI;
+
+internal class UGUITests
+{
+    Scene m_Scene;
+    [SetUp]
+    public void SetUp()
+    {
+        // Ensure that the scene is clean before starting the test
+        m_Scene = EditorSceneManager.NewScene(NewSceneSetup.DefaultGameObjects);
+    }
+
+    [TearDown]
+    public void TearDown()
+    {
+        EditorSceneManager.CloseScene(m_Scene, true);
+    }
+
+    [Test]
+    [Category("UGUITests")]
+    // This test checks that when the Input System is enabled the EventSystem GameObject is created with the
+    // InputSystemUIInputModule component.
+    public void UGUITests_Editor_EventSystemGameObjectUsesUIInputModule()
+    {
+        m_Scene = EditorSceneManager.NewScene(NewSceneSetup.DefaultGameObjects);
+
+        // Creates the EventSystem GameObject using the Editor menu
+        string menuItem = "GameObject/UI/Event System";
+        Assert.AreEqual(2, m_Scene.rootCount);
+        EditorApplication.ExecuteMenuItem(menuItem);
+        Assert.AreEqual(3, m_Scene.rootCount);
+
+        // Get the EventSystem GameObject from the scene to check that it has the correct input module
+        var rootGameObjects = m_Scene.GetRootGameObjects();
+        GameObject eventSystem = rootGameObjects[2].GetComponent<EventSystem>().gameObject;
+
+        Assert.IsNotNull(eventSystem);
+        Assert.IsNotNull(eventSystem.GetComponent<InputSystemUIInputModule>());
+    }
+}
+
+#endif

Assets/Tests/InputSystem.Editor/UGUITests.cs.meta

@@ -15,6 +15,10 @@ however, it has to be formatted properly to pass verification tests.
 - NullReferenceException thrown when right-clicking an empty Action Map list in Input Actions Editor windows [ISXB-833](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-833).
 - Fixed an issue where `System.ObjectDisposedException` would be thrown when deleting the last ActionMap item in the Input Actions Asset editor.
 
+### Changed
+- For Unity 6.0 and above, when an `EventSystem` GameObject is created in the Editor it will have the
+`InputSystemUIInputModule` by default if the Input System package is installed and enabled.
+
 ## [1.8.1] - 2024-03-14
 
 ### Fixed

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -2,14 +2,25 @@
 using System;
 using System.Linq;
 using UnityEditor;
+using UnityEditor.EventSystems;
+using UnityEngine.InputSystem.Editor;
 
 ////TODO: add button to automatically set up gamepad mouse cursor support
 
 namespace UnityEngine.InputSystem.UI.Editor
 {
     [CustomEditor(typeof(InputSystemUIInputModule))]
+    [InitializeOnLoad]
     internal class InputSystemUIInputModuleEditor : UnityEditor.Editor
     {
+        static InputSystemUIInputModuleEditor()
+        {
+#if UNITY_6000_0_OR_NEWER && ENABLE_INPUT_SYSTEM
+            InputModuleComponentFactory.SetInputModuleComponentOverride(
+                go => ObjectFactory.AddComponent<InputSystemUIInputModule>(go));
+#endif
+        }
+
         private static InputActionReference GetActionReferenceFromAssets(InputActionReference[] actions, params string[] actionNames)
         {
             foreach (var actionName in actionNames)