fix compile errors 2019.4. fixed package validation errors.

Author: Karl Henkel

Debug/Editor/Guides.cs

@@ -9,7 +9,7 @@ static class GuidesSettingsProvider
     {
         const string k_PreferencesPath = "Preferences/Scene Guides";
         static Settings s_Settings;
-        public static Settings settings => s_Settings ??= new Settings("com.unity.scene-guides");
+        public static Settings settings => s_Settings ?? (s_Settings = new Settings("com.unity.scene-guides"));
 
         [SettingsProvider]
         static SettingsProvider CreateSettingsProvider()
@@ -89,11 +89,19 @@ static void DrawLine(Vector3 from, Vector3 to, Color color, float occludedTint =
         {
             Handles.color = color;
             Handles.zTest = CompareFunction.LessEqual;
+#if UNITY_2021_1_OR_NEWER
             Handles.DrawLine(from, to, thickness);
+#else
+            Handles.DrawLine(from, to);
+#endif
 
             Handles.color = color * occludedTint;
             Handles.zTest = CompareFunction.Greater;
+#if UNITY_2021_1_OR_NEWER
             Handles.DrawLine(from, to, thickness);
+#else
+            Handles.DrawLine(from, to);
+#endif
         }
     }
 }

Runtime/Core/MeshUtility.cs

@@ -662,7 +662,7 @@ internal static void RestoreParticleSystem(ProBuilderMesh pbmesh)
 #endif
         }
 
-        public static Bounds GetBounds(this ProBuilderMesh mesh)
+        internal static Bounds GetBounds(this ProBuilderMesh mesh)
         {
             if (mesh.mesh != null)
                 return mesh.mesh.bounds;

Runtime/MeshOperations/MeshTransform.cs

@@ -11,7 +11,7 @@ public static class MeshTransform
         /// <param name="mesh">The <see cref="ProBuilderMesh"/> to adjust vertices for a new pivot point.</param>
         /// <param name="pivotLocation">The new pivot point is either the center of the mesh bounding box, or
         /// the bounds center - extents.</param>
-        public static void SetPivot(this ProBuilderMesh mesh, PivotLocation pivotLocation)
+        internal static void SetPivot(this ProBuilderMesh mesh, PivotLocation pivotLocation)
         {
             var bounds = mesh.GetBounds();
             var pivot = pivotLocation == PivotLocation.Center ? bounds.center : bounds.center - bounds.extents;