FIX: Delayed input backend prompt to make sure asset import is not interrupted (ISXB-608) (#2107)

Author: ritamerkl

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -11,8 +11,10 @@ however, it has to be formatted properly to pass verification tests.
 ## [Unreleased] - yyyy-mm-dd
 
 ### Fixed
+- Fixed an issue where the prompt to enable the InputSystem backends would interrupt the import of large assets.
 - Fixed Cut Mode for Action Maps and Actions to make renaming disabled. [ISXB-1155](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-1155)
 
+
 ## [1.12.0] - 2025-01-15
 
 ### Fixed

Packages/com.unity.inputsystem/InputSystem/InputSystem.cs

@@ -3599,14 +3599,29 @@ internal static void InitializeInEditor(IInputRuntime runtime = null)
             }
 
             Debug.Assert(settings != null);
-            #if UNITY_EDITOR
             Debug.Assert(EditorUtility.InstanceIDToObject(settings.GetInstanceID()) != null,
                 "InputSettings has lost its native object");
-            #endif
 
             // If native backends for new input system aren't enabled, ask user whether we should
             // enable them (requires restart). We only ask once per session and don't ask when
             // running in batch mode.
+            // The warning is delayed to delay call (called a short while after the Asset are loaded, on Inspector update) to make sure it doesn't pop up while the editor is still loading or assets are not fully loaded -
+            // this would cancel the import of large assets that are dependent on the InputSystem package and import it as a dependency.
+            EditorApplication.delayCall += ShowRestartWarning;
+
+#if UNITY_INPUT_SYSTEM_PROJECT_WIDE_ACTIONS
+            // Make sure project wide input actions are enabled.
+            // Note that this will always fail if entering play-mode within editor since not yet in play-mode.
+            EnableActions();
+#endif
+
+            RunInitialUpdate();
+
+            k_InputInitializeInEditorMarker.End();
+        }
+
+        private static void ShowRestartWarning()
+        {
             if (!s_SystemObject.newInputBackendsCheckedAsEnabled &&
                 !EditorPlayerSettingHelpers.newSystemBackendsEnabled &&
                 !s_Manager.m_Runtime.isInBatchMode)
@@ -3622,16 +3637,7 @@ internal static void InitializeInEditor(IInputRuntime runtime = null)
                 }
             }
             s_SystemObject.newInputBackendsCheckedAsEnabled = true;
-
-#if UNITY_INPUT_SYSTEM_PROJECT_WIDE_ACTIONS
-            // Make sure project wide input actions are enabled.
-            // Note that this will always fail if entering play-mode within editor since not yet in play-mode.
-            EnableActions();
-#endif
-
-            RunInitialUpdate();
-
-            k_InputInitializeInEditorMarker.End();
+            EditorApplication.delayCall -= ShowRestartWarning;
         }
 
         internal static void OnPlayModeChange(PlayModeStateChange change)