Fix warning in HDAdditionalLightData OnValidate (#885)

* fix warning in HDAdditionalLightData OnValidate

* Changelog

* Avoid calling update

Co-authored-by: sebastienlagarde <sebastien@unity3d.com>

Author: pmavridis

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -685,6 +685,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed a serialization issue, preventing quality level parameters to undo/redo and update scene view on change.
 - Fixed an exception occuring when a camera doesn't have an HDAdditionalCameraData (1254383).
 - Fixed ray tracing with XR single-pass.
+- Fixed warning in HDAdditionalLightData OnValidate (cases 1250864, 1244578)
 
 ### Changed
 - Improve MIP selection for decals on Transparents

com.unity.render-pipelines.high-definition/Runtime/Lighting/Light/HDAdditionalLightData.cs

@@ -1586,6 +1586,7 @@ internal Light legacyLight
         internal MeshRenderer emissiveMeshRenderer { get; private set; }
 
 #if UNITY_EDITOR
+        bool m_NeedsPrefabInstanceCheck = false;
         bool needRefreshPrefabInstanceEmissiveMeshes = false;
 #endif
         bool needRefreshEmissiveMeshesFromTimeLineUpdate = false;
@@ -2292,6 +2293,14 @@ void LateUpdate()
 #endif
 
 #if UNITY_EDITOR
+
+            // If modification are due to change on prefab asset that are non overridden on this prefab instance
+            if (m_NeedsPrefabInstanceCheck && PrefabUtility.IsPartOfPrefabInstance(this) && ((PrefabUtility.GetCorrespondingObjectFromOriginalSource(this) as HDAdditionalLightData)?.needRefreshPrefabInstanceEmissiveMeshes ?? false))
+            {
+                needRefreshPrefabInstanceEmissiveMeshes = true;
+            }
+            m_NeedsPrefabInstanceCheck = false;
+
             // Update the list of overlapping lights for the LightOverlap scene view mode
             if (IsOverlapping())
                 s_overlappingHDLights.Add(this);
@@ -2499,13 +2508,9 @@ void OnValidate()
             RefreshCachedShadow();
 
 #if UNITY_EDITOR
-            // If modification are due to change on prefab asset that are non overridden on this prefab instance
-            if (PrefabUtility.IsPartOfPrefabInstance(this) && ((PrefabUtility.GetCorrespondingObjectFromOriginalSource(this) as HDAdditionalLightData)?.needRefreshPrefabInstanceEmissiveMeshes ?? false))
-            {
-                // As we cannot Create/Destroy in OnValidate, delay call to next Update
-                // To do this, wo set the same flag on prefab instances
-                needRefreshPrefabInstanceEmissiveMeshes = true;
-            }
+            // If modification are due to change on prefab asset, we want to have prefab instances to self-update, but we cannot check in OnValidate if this is part of
+            // prefab instance. So we delay the check on next update (and before teh LateUpdate logic)
+            m_NeedsPrefabInstanceCheck = true;
 #endif
         }