Revit_Engine: fix the copy of the DiffingConfig properties

Revit_Engine/Compute/RevitDiffing.cs

@@ -144,6 +144,7 @@ private static Diff Diffing(IEnumerable<object> pastObjects, IEnumerable<object>
             }
 
             // Checks and setup of DiffingConfig/ComparisonConfig.
+            diffConfig = diffConfig ?? new DiffingConfig();
             RevitComparisonConfig rcc = diffConfig?.ComparisonConfig as RevitComparisonConfig;
             if (rcc == null)
             {
@@ -152,11 +153,6 @@ private static Diff Diffing(IEnumerable<object> pastObjects, IEnumerable<object>
                 if (diffConfig != null)
                     BH.Engine.Reflection.Modify.CopyPropertiesFromParent(rcc, diffConfig?.ComparisonConfig);
             }
-            DiffingConfig diffConfigClone = GetRevitDiffingConfig(rcc);
-
-            //Add any custom object difference compares on the provided diff config
-            if (diffConfig.CustomObjectDifferencesComparers != null && diffConfig.CustomObjectDifferencesComparers.Any())
-                diffConfigClone.CustomObjectDifferencesComparers.AddRange(diffConfig.CustomObjectDifferencesComparers);
 
             // Get the past and following RevitIdentifiers fragments.
             IEnumerable<RevitIdentifiers> pastIdFragments = pastObjects.OfType<IBHoMObject>().Select(obj => obj.GetRevitIdentifiers()).Where(x => x != null);
@@ -206,20 +202,23 @@ private static Diff Diffing(IEnumerable<object> pastObjects, IEnumerable<object>
                 return null;
             }
 
+            // Get a Revit-customised instance of DiffingConfig.
+            DiffingConfig diffConfigClone = GetRevitDiffingConfig(rcc, diffConfig);
+
             //Compute the diffing through DiffWithCustomIds making use of the ids extracted from the objects
             Diff revitDiff = BH.Engine.Diffing.Compute.DiffWithCustomIds(pastObjects.ToList(), pastIds, followingObjects.ToList(), followingIds, diffConfigClone);
             return revitDiff;
         }
 
-        private static DiffingConfig GetRevitDiffingConfig(RevitComparisonConfig rcc)
+        private static DiffingConfig GetRevitDiffingConfig(RevitComparisonConfig rcc, DiffingConfig originalDiffConfig = null)
         {
             rcc = rcc ?? new RevitComparisonConfig();
 
             rcc.TypeExceptions.Add(typeof(RevitParameter));
             rcc.TypeExceptions.Add(typeof(RevitPulledParameters));
             rcc.TypeExceptions.Add(typeof(RevitParametersToPush));
 
-            return new DiffingConfig()
+            DiffingConfig result = new DiffingConfig()
             {
                 ComparisonConfig = rcc,
                 CustomObjectDifferencesComparers = new List<Func<object, object, BaseComparisonConfig, List<IPropertyDifference>>>()
@@ -228,8 +227,21 @@ private static DiffingConfig GetRevitDiffingConfig(RevitComparisonConfig rcc)
                     (obj1, obj2, baseComparisonConfig) => { return Query.RevitRevitParametersToPushDifferences(obj1, obj2, baseComparisonConfig); }
                 }
             };
-        }
-    }
-}
 
+            // If an instance of a diffingConfig was provided, copy its properties.
+            if (originalDiffConfig != null)
+            {
+                //Add any custom object difference compares provided via the original diff config.
+                if (originalDiffConfig.CustomObjectDifferencesComparers != null && originalDiffConfig.CustomObjectDifferencesComparers.Any())
+                    result.CustomObjectDifferencesComparers.AddRange(originalDiffConfig.CustomObjectDifferencesComparers.Except(result.CustomObjectDifferencesComparers));
+
+                result.AllowDuplicateIds = originalDiffConfig.AllowDuplicateIds;
+                result.EnablePropertyDiffing = originalDiffConfig.EnablePropertyDiffing;
+                result.IncludeUnchangedObjects = originalDiffConfig.IncludeUnchangedObjects;
+                result.ComparisonConfig = originalDiffConfig.ComparisonConfig;
+            }
 
+            return result;
+        }
+    }
+}