Fix duplicate types exception on WinRT interfaces (#23402)

* Fix duplicate types exception on WinRT interfaces

* Maintaining order

1 files changed, 8 insertions, 5 deletions

diff --git a/src/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/RuntimeBinder.cs b/src/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/RuntimeBinder.cs
index 8580cbadb3..8a65a132db 100644
--- a/src/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/RuntimeBinder.cs
+++ b/src/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/RuntimeBinder.cs
@@ -635,15 +635,18 @@ namespace Microsoft.CSharp.RuntimeBinder
                 callingType = (AggregateType)callingObjectType;
             }
 
-            List<CType> callingTypes = new List<CType>();
-
             // The C# binder expects that only the base virtual method is inserted
             // into the list of candidates, and only the type containing the base
             // virtual method is inserted into the list of types. However, since we
             // don't want to do all the logic, we're just going to insert every type
             // that has a member of the given name, and allow the C# binder to filter
             // out all overrides.
-            //
+
+            // CONSIDER: using a hashset to filter out duplicate interface types.
+            // Adopt a smarter algorithm to filter types before creating the exception.
+            HashSet<CType> distinctCallingTypes = new HashSet<CType>();
+            List<CType> callingTypes = new List<CType>();
+
             // Find that set of types now.
             symbmask_t mask = symbmask_t.MASK_MethodSymbol;
             switch (kind)
@@ -664,7 +667,7 @@ namespace Microsoft.CSharp.RuntimeBinder
             bool bIsConstructor = name == NameManager.GetPredefinedName(PredefinedName.PN_CTOR);
             foreach(AggregateType t in callingType.TypeHierarchy)
             {
-                if (_symbolTable.AggregateContainsMethod(t.GetOwningAggregate(), Name, mask))
+                if (_symbolTable.AggregateContainsMethod(t.GetOwningAggregate(), Name, mask) && distinctCallingTypes.Add(t))
                 {
                     callingTypes.Add(t);
                 }
@@ -684,7 +687,7 @@ namespace Microsoft.CSharp.RuntimeBinder
 
                 foreach (AggregateType t in callingType.GetWinRTCollectionIfacesAll(SymbolLoader).Items)
                 {
-                    if (_symbolTable.AggregateContainsMethod(t.GetOwningAggregate(), Name, mask))
+                    if (_symbolTable.AggregateContainsMethod(t.GetOwningAggregate(), Name, mask) && distinctCallingTypes.Add(t))
                     {
                         callingTypes.Add(t);
                     }