From 69426524a6fcc4e2c51135ec011824a109491570 Mon Sep 17 00:00:00 2001
From: David Wrighton <davidwr@microsoft.com>
Date: Tue, 11 May 2021 14:46:14 -0700
Subject: [PATCH] Add support for interface variance - Fix incorrect details in
 interface variance test - Add loop over actually implemented interfaces to
 try and find possible matches in a way which matches the behavior of normal
 interface variance matching

---
 src/coreclr/vm/methodtable.cpp                | 33 +++++++++++++++++--
 .../InterfaceVariance/InterfaceVariance.il    | 15 +++++----
 2 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/src/coreclr/vm/methodtable.cpp b/src/coreclr/vm/methodtable.cpp
index 9084c3fe5c20eb..a4020a875afb84 100644
--- a/src/coreclr/vm/methodtable.cpp
+++ b/src/coreclr/vm/methodtable.cpp
@@ -9208,6 +9208,37 @@ MethodTable::ResolveVirtualStaticMethod(MethodTable* pInterfaceType, MethodDesc*
                 {
                     return pMD;
                 }
+
+                if (pInterfaceType->HasVariance())
+                {
+                    // Variant interface dispatch
+                    MethodTable::InterfaceMapIterator it = IterateInterfaceMap();
+                    while (it.Next())
+                    {
+                        if (it.GetInterface() == pInterfaceType)
+                        {
+                            // This is the variant interface check logic, skip the 
+                            continue;
+                        }
+
+                        if (!it.GetInterface()->HasSameTypeDefAs(pInterfaceType))
+                        {
+                            // Variance matches require a typedef match
+                            continue;
+                        }
+
+                        if (it.GetInterface()->CanCastTo(pInterfaceType, NULL))
+                        {
+                            // Variant matching interface found
+                            // Attempt to resolve on variance matched interface
+                            pMD = pMT->TryResolveVirtualStaticMethodOnThisType(it.GetInterface(), pInterfaceMD);
+                            if (pMD != nullptr)
+                            {
+                                return pMD;
+                            }
+                        }
+                    }
+                }
             }
         }
     }
@@ -9238,8 +9269,6 @@ MethodTable::TryResolveVirtualStaticMethodOnThisType(MethodTable* pInterfaceType
     // This gets the count out of the metadata interface.
     uint32_t dwNumberMethodImpls = hEnumMethodImpl.EnumMethodImplGetCount();
 
-    // TODO: support type-equivalent interface type matches and variant interface scenarios
-
     // Iterate through each MethodImpl declared on this class
     for (uint32_t i = 0; i < dwNumberMethodImpls; i++)
     {
diff --git a/src/tests/Loader/classloader/StaticVirtualMethods/InterfaceVariance/InterfaceVariance.il b/src/tests/Loader/classloader/StaticVirtualMethods/InterfaceVariance/InterfaceVariance.il
index 88cc8638c5da48..63eeb79f937ab9 100644
--- a/src/tests/Loader/classloader/StaticVirtualMethods/InterfaceVariance/InterfaceVariance.il
+++ b/src/tests/Loader/classloader/StaticVirtualMethods/InterfaceVariance/InterfaceVariance.il
@@ -12,7 +12,8 @@
   .method public newslot virtual abstract static int32 Method() cil managed noinlining
   {
   } // end of method Method
-} // end of class InterfaceScenario1
+} // end of class InterfaceScenario1`1
+
 .class interface public abstract auto ansi InterfaceScenario2`1<- T>
 {
   .method public newslot virtual abstract static int32 Method() cil managed noinlining
@@ -43,7 +44,7 @@
 
 .class public auto ansi BaseScenario2
        extends [System.Runtime]System.Object
-       implements class InterfaceScenario1`1<string>, class InterfaceScenario1`1<object>
+       implements class InterfaceScenario2`1<string>, class InterfaceScenario2`1<object>
 {
   // NOTE: The order of the methods in this .il file is important as it controls the MethodImpl record creation order
   .method public static int32 Method() cil managed noinlining
@@ -77,18 +78,18 @@
 {
     .method public static int32 Method() cil managed noinlining
   {
-    .override method int32 class InterfaceScenario2`1<string>::Method()
+    .override method int32 class InterfaceScenario2`1<object>::Method()
     ldc.i4 6
     ret
   } // end of method Method
 
   .method public static int32 Method2() cil managed noinlining
   {
-    .override method int32 class InterfaceScenario2`1<string>::Method2()
+    .override method int32 class InterfaceScenario2`1<object>::Method2()
     ldc.i4 7
     ret
   } // end of method Method
-} // end of class DerivedScenario1
+} // end of class DerivedScenario2
 
 
 .class public auto ansi TestEntrypoint
@@ -106,7 +107,7 @@
     ret
   } // end of method Test_Scenario1
 
-  .method public static string Test_Scenario2_1<T, (class InterfaceScenario1`1<!!0>) ImplType>() cil managed noinlining
+  .method public static string Test_Scenario2_1<T, (class InterfaceScenario2`1<!!0>) ImplType>() cil managed noinlining
   {
     // Variant dispatch to method on base type
     .locals init (int32 V_1)
@@ -118,7 +119,7 @@
     ret
   } // end of method Test_Scenario1
 
-  .method public static string Test_Scenario2_2<T, (class InterfaceScenario1`1<!!0>) ImplType>() cil managed noinlining
+  .method public static string Test_Scenario2_2<T, (class InterfaceScenario2`1<!!0>) ImplType>() cil managed noinlining
   {
     // Variant dispatch to method on base type
     .locals init (int32 V_1)