Open types can exist as entries in interface map

src/coreclr/vm/methodtable.cpp

@@ -1577,6 +1577,7 @@ BOOL MethodTable::CanCastByVarianceToInterfaceOrDelegate(MethodTable *pTargetMT,
 
     // Shortcut for generic approx type scenario
     if (pMTInterfaceMapOwner != NULL &&
+        !pMTInterfaceMapOwner->ContainsGenericVariables() &&
         IsSpecialMarkerTypeForGenericCasting() &&
         GetTypeDefRid() == pTargetMT->GetTypeDefRid() &&
         GetModule() == pTargetMT->GetModule() &&
@@ -1603,7 +1604,7 @@ BOOL MethodTable::CanCastByVarianceToInterfaceOrDelegate(MethodTable *pTargetMT,
         for (DWORD i = 0; i < inst.GetNumArgs(); i++)
         {
             TypeHandle thArg = inst[i];
-            if (IsSpecialMarkerTypeForGenericCasting() && pMTInterfaceMapOwner)
+            if (IsSpecialMarkerTypeForGenericCasting() && pMTInterfaceMapOwner && pMTInterfaceMapOwner->ContainsGenericVariables())
             {
                 thArg = pMTInterfaceMapOwner;
             }
@@ -9820,7 +9821,7 @@ PTR_MethodTable MethodTable::InterfaceMapIterator::GetInterface(MethodTable* pMT
     CONTRACT_END;
 
     MethodTable *pResult = m_pMap->GetMethodTable();
-    if (pResult->IsSpecialMarkerTypeForGenericCasting())
+    if (pResult->IsSpecialMarkerTypeForGenericCasting() && pMTOwner->ContainsGenericVariables())
     {
         TypeHandle ownerAsInst[MaxGenericParametersForSpecialMarkerType];
         for (DWORD i = 0; i < MaxGenericParametersForSpecialMarkerType; i++)

src/coreclr/vm/methodtable.h

@@ -2245,7 +2245,8 @@ class MethodTable
             {
                 if (pCurrentMethodTable->HasSameTypeDefAs(pMT) && 
                     pMT->HasInstantiation() && 
-                    pCurrentMethodTable->IsSpecialMarkerTypeForGenericCasting() && 
+                    pCurrentMethodTable->IsSpecialMarkerTypeForGenericCasting() &&
+                    !pMTOwner->ContainsGenericVariables() &&
                     pMT->GetInstantiation().ContainsAllOneType(pMTOwner))
                 {
                     exactMatch = true;

src/coreclr/vm/methodtable.inl

@@ -1571,7 +1571,7 @@ FORCEINLINE BOOL MethodTable::ImplementsInterfaceInline(MethodTable *pInterface)
     while (--numInterfaces);
 
     // Second scan, looking for the curiously recurring generic scenario
-    if (pInterface->HasInstantiation() && pInterface->GetInstantiation().ContainsAllOneType(this))
+    if (pInterface->HasInstantiation() && !ContainsGenericVariables() && pInterface->GetInstantiation().ContainsAllOneType(this))
     {
         numInterfaces = GetNumInterfaces();
         pInfo = GetInterfaceMap();

src/coreclr/vm/methodtablebuilder.cpp

@@ -9101,8 +9101,13 @@ MethodTableBuilder::LoadExactInterfaceMap(MethodTable *pMT)
     MethodTable **pExactMTs = (MethodTable**) _alloca(sizeof(MethodTable *) * nInterfacesCount);
     BOOL duplicates;
     bool retry = false;
-    bool retryWithExactInterfaces = !pMT->IsValueType() || pMT->IsSharedByGenericInstantiations(); // Always use exact loading behavior with classes or shared generics, as they have to deal with inheritance, and the
-                                                                                          // inexact matching logic for classes would be more complex to write.
+
+    // Always use exact loading behavior with classes or shared generics, as they have to deal with inheritance, and the
+    // inexact matching logic for classes would be more complex to write.
+    // Also always use the exact loading behavior with any generic that contains generic variables, as the open type is used
+    // to represent a type instantiated over its own generic variables, and the special marker type is currently the open type
+    // and we make this case distinguishable by simply disallowing the optimization in those cases.
+    bool retryWithExactInterfaces = !pMT->IsValueType() || pMT->IsSharedByGenericInstantiations() || pMT->ContainsGenericVariables();
 
     DWORD nAssigned = 0;
     do
@@ -9132,7 +9137,7 @@ MethodTableBuilder::LoadExactInterfaceMap(MethodTable *pMT)
                                                                                 (const Substitution*)0,
                                                                                 retryWithExactInterfaces ? NULL : pMT).GetMethodTable();
 
-            bool uninstGenericCase = pNewIntfMT->IsSpecialMarkerTypeForGenericCasting();
+            bool uninstGenericCase = !retryWithExactInterfaces && pNewIntfMT->IsSpecialMarkerTypeForGenericCasting();
 
             duplicates |= InsertMethodTable(pNewIntfMT, pExactMTs, nInterfacesCount, &nAssigned);
 

src/tests/Loader/classloader/generics/Instantiation/Positive/CuriouslyRecurringThroughInterface.cs

@@ -0,0 +1,23 @@
+namespace CuriouslyRecurringPatternThroughInterface
+{
+    interface IGeneric<T_IGeneric>
+    {
+    }
+    interface ICuriouslyRecurring<T_ICuriouslyRecurring> : IGeneric<CuriouslyRecurringThroughInterface<T_ICuriouslyRecurring>>
+    {
+    }
+    class CuriouslyRecurringThroughInterface<T_CuriouslyRecurringThroughInterface> : ICuriouslyRecurring<T_CuriouslyRecurringThroughInterface>
+    {
+    }
+
+    class Program
+    {
+        static object _o;
+        static int Main(string[] args)
+        {
+            // Test that the a generic using a variant of the curiously recurring pattern involving an interface can be loaded.
+            _o = typeof(CuriouslyRecurringThroughInterface<int>);
+            return 100;
+        }
+    }
+}

src/tests/Loader/classloader/generics/Instantiation/Positive/CuriouslyRecurringThroughInterface.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <OutputType>Exe</OutputType>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <CLRTestPriority>1</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="CuriouslyRecurringThroughInterface.cs" />
+  </ItemGroup>
+</Project>