Allow reabstraction of default interface methods (#23313)

Allow the runtime to load types with incomplete interface implementations. With this change, we allow (in pseudo-C#):

```csharp
interface IFoo { void Frob() { } } 
interface IBar : IFoo { abstract void IFoo.Frob() }
class Fooer : IBar { }
```

Calling IFoo.Frob on an instance of `Fooer` will result in new exception being thrown because the default implementation of `IFoo.Frob` was re-abstracted by `IBar`.

5 files changed, 213 insertions, 8 deletions

diff --git a/tests/src/reflection/DefaultInterfaceMethods/Emit.cs b/tests/src/reflection/DefaultInterfaceMethods/Emit.cs
index e57f7c1f6f..4cd872ad64 100644
--- a/tests/src/reflection/DefaultInterfaceMethods/Emit.cs
+++ b/tests/src/reflection/DefaultInterfaceMethods/Emit.cs
@@ -73,14 +73,66 @@ class Program
         // Test what we created
         //
 
-        object o = Activator.CreateInstance(fooType);
-
         int result = 0;
 
-        result |= (int)ifooType.GetMethod("InstanceMethod").Invoke(o, null);
-        result |= (int)ifooType.GetMethod("DefaultMethod").Invoke(o, null);
-        result |= (int)ifooType.GetMethod("InterfaceMethod").Invoke(o, null);
+        {
+            object o = Activator.CreateInstance(fooType);
+
+            result |= (int)ifooType.GetMethod("InstanceMethod").Invoke(o, null);
+            result |= (int)ifooType.GetMethod("DefaultMethod").Invoke(o, null);
+            result |= (int)ifooType.GetMethod("InterfaceMethod").Invoke(o, null);
+        }
+
+        //
+        // Set up the IBaz interface
+        //
+
+        var ibazType = modb.DefineType("IBaz", TypeAttributes.Interface | TypeAttributes.Abstract | TypeAttributes.Public, null, new Type[] { ifooType });
+
+        // Override the default interface method on IFoo with a reabstraction
+        {
+            var mb = ibazType.DefineMethod("DefaultMethodImpl", MethodAttributes.Public | MethodAttributes.Virtual | MethodAttributes.NewSlot | MethodAttributes.Final | MethodAttributes.Abstract, typeof(int), Type.EmptyTypes);
+            ibazType.DefineMethodOverride(mb, ifooType.GetMethod("DefaultMethod"));
+        }
+
+        // Override the regular interface method on IFoo with a reabstraction
+        {
+            var mb = ibazType.DefineMethod("InterfaceMethodImpl", MethodAttributes.Public | MethodAttributes.Virtual | MethodAttributes.NewSlot | MethodAttributes.Final | MethodAttributes.Abstract, typeof(int), Type.EmptyTypes);
+            ibazType.DefineMethodOverride(mb, ifooType.GetMethod("InterfaceMethod"));
+        }
+
+        ibazType.CreateTypeInfo();
+
+        //
+        // Make a simple Baz class that implements IBaz
+        //
+
+        var bazType = modb.DefineType("Baz", TypeAttributes.Class | TypeAttributes.Public, typeof(object), new Type[] { ibazType });
+
+        bazType.CreateTypeInfo();
+
+        {
+            object o = Activator.CreateInstance(bazType);
+
+            try
+            {
+                ifooType.GetMethod("DefaultMethod").Invoke(o, null);
+            }
+            catch (EntryPointNotFoundException)
+            {
+                result |= 0x10;
+            }
+
+            try
+            {
+                ifooType.GetMethod("InterfaceMethod").Invoke(o, null);
+            }
+            catch (EntryPointNotFoundException)
+            {
+                result |= 0x20;
+            }
+        }
 
-        return result == 0x07 ? 100 : result;
+        return result == 0x37 ? 100 : result;
     }
 }
diff --git a/tests/src/reflection/DefaultInterfaceMethods/GetInterfaceMapConsumer.cs b/tests/src/reflection/DefaultInterfaceMethods/GetInterfaceMapConsumer.cs
index ecb6373291..845cf49005 100644
--- a/tests/src/reflection/DefaultInterfaceMethods/GetInterfaceMapConsumer.cs
+++ b/tests/src/reflection/DefaultInterfaceMethods/GetInterfaceMapConsumer.cs
@@ -85,12 +85,86 @@ class Program
                 return 10;
         }
 
+
+        {
+            var map = typeof(Reabstractor).GetInterfaceMap(typeof(IFoo));
+
+            int foundMatchMask = 0;
+
+            MethodInfo ifooDefaultMethod = typeof(IFoo).GetMethod("DefaultMethod");
+            MethodInfo ifooOtherMethod = typeof(IFoo).GetMethod("OtherMethod");
+
+            for (int i = 0; i < map.InterfaceMethods.Length; i++)
+            {
+                MethodInfo declMethod = map.InterfaceMethods[i];
+                MethodInfo implMethod = map.TargetMethods[i];
+
+                Console.Write("{0} ({1}) - {2} ({3}) - ", declMethod, declMethod.DeclaringType, implMethod, implMethod?.DeclaringType);
+
+                if (declMethod.Equals(ifooDefaultMethod))
+                {
+                    foundMatchMask |= 1;
+                    CheckEqual(ref failed, implMethod, null);
+                }
+                else if (declMethod.Equals(ifooOtherMethod))
+                {
+                    foundMatchMask |= 2;
+                    CheckEqual(ref failed, implMethod, null);
+                }
+                else
+                {
+                    Console.WriteLine("UNEXPECTED");
+                    failed = true;
+                }
+            }
+
+            if (foundMatchMask != 3)
+                return 10;
+        }
+
+        {
+            var map = typeof(Diamond).GetInterfaceMap(typeof(IFoo));
+
+            int foundMatchMask = 0;
+
+            MethodInfo ifooDefaultMethod = typeof(IFoo).GetMethod("DefaultMethod");
+            MethodInfo ifooOtherMethod = typeof(IFoo).GetMethod("OtherMethod");
+
+            for (int i = 0; i < map.InterfaceMethods.Length; i++)
+            {
+                MethodInfo declMethod = map.InterfaceMethods[i];
+                MethodInfo implMethod = map.TargetMethods[i];
+
+                Console.Write("{0} ({1}) - {2} ({3}) - ", declMethod, declMethod.DeclaringType, implMethod, implMethod?.DeclaringType);
+
+                if (declMethod.Equals(ifooDefaultMethod))
+                {
+                    foundMatchMask |= 1;
+                    CheckEqual(ref failed, implMethod, ifooDefaultMethod);
+                }
+                else if (declMethod.Equals(ifooOtherMethod))
+                {
+                    foundMatchMask |= 2;
+                    CheckEqual(ref failed, implMethod, null);
+                }
+                else
+                {
+                    Console.WriteLine("UNEXPECTED");
+                    failed = true;
+                }
+            }
+
+            if (foundMatchMask != 3)
+                return 10;
+        }
+
+
         return failed ? -1 : 100;
     }
 
     static void CheckEqual(ref bool failed, MethodInfo method1, MethodInfo method2)
     {
-        if (method1.Equals(method2))
+        if (Object.Equals(method1, method2))
             Console.WriteLine("OK");
         else
         {
@@ -98,4 +172,4 @@ class Program
             failed = true;
         }
     }
-}
\ No newline at end of file
+}
diff --git a/tests/src/reflection/DefaultInterfaceMethods/GetInterfaceMapProvider.il b/tests/src/reflection/DefaultInterfaceMethods/GetInterfaceMapProvider.il
index 03785988e0..9ad1a7db4f 100644
--- a/tests/src/reflection/DefaultInterfaceMethods/GetInterfaceMapProvider.il
+++ b/tests/src/reflection/DefaultInterfaceMethods/GetInterfaceMapProvider.il
@@ -43,6 +43,29 @@
   }
 }
 
+.class interface public abstract auto ansi IBaz implements IFoo
+{
+  .method public hidebysig newslot virtual final instance int32 OtherMethod(int32) cil managed
+  {
+    .override IFoo::OtherMethod
+    ldarg.1
+    ret
+  }
+}
+
+.class interface public abstract auto ansi IReabstractor implements IFoo
+{
+  .method public hidebysig newslot abstract virtual final instance int32 DefaultMethod(int32) cil managed
+  {
+    .override IFoo::DefaultMethod
+  }
+
+  .method public hidebysig newslot abstract virtual final instance int32 OtherMethod(int32) cil managed
+  {
+    .override IFoo::OtherMethod
+  }
+}
+
 .class interface public abstract auto ansi IFoo`1<T>
 {
   .method public hidebysig newslot virtual instance valuetype [mscorlib]System.RuntimeTypeHandle DefaultMethod() cil managed
@@ -79,3 +102,29 @@
     ret
   }
 }
+
+.class public auto ansi beforefieldinit Reabstractor
+       extends [mscorlib]System.Object
+       implements IReabstractor
+{
+  .method public hidebysig specialname rtspecialname 
+          instance void .ctor() cil managed
+  {
+    ldarg.0
+    call instance void [mscorlib]System.Object::.ctor()
+    ret
+  }
+}
+
+.class public auto ansi beforefieldinit Diamond
+       extends [mscorlib]System.Object
+       implements IBar, IBaz
+{
+  .method public hidebysig specialname rtspecialname 
+          instance void .ctor() cil managed
+  {
+    ldarg.0
+    call instance void [mscorlib]System.Object::.ctor()
+    ret
+  }
+}
diff --git a/tests/src/reflection/DefaultInterfaceMethods/InvokeConsumer.cs b/tests/src/reflection/DefaultInterfaceMethods/InvokeConsumer.cs
index 4ac82f9a1b..247b830b24 100644
--- a/tests/src/reflection/DefaultInterfaceMethods/InvokeConsumer.cs
+++ b/tests/src/reflection/DefaultInterfaceMethods/InvokeConsumer.cs
@@ -38,6 +38,15 @@ class Program
         if (!((RuntimeTypeHandle)typeof(IFoo<Fooer>).GetMethod("InstanceMethod").Invoke(new ValueFooer(), new object[] { })).Equals(typeof(Fooer[]).TypeHandle))
             return 33;
 
+        try
+        {
+            typeof(IFoo).GetMethod("DefaultMethod").Invoke(new Reabstractor(), new object[] { 1 });
+            return 501;
+        }
+        catch (EntryPointNotFoundException)
+        {
+        }
+
         return 100;
     }
 }
diff --git a/tests/src/reflection/DefaultInterfaceMethods/InvokeProvider.il b/tests/src/reflection/DefaultInterfaceMethods/InvokeProvider.il
index d1f6e73af8..4c43089571 100644
--- a/tests/src/reflection/DefaultInterfaceMethods/InvokeProvider.il
+++ b/tests/src/reflection/DefaultInterfaceMethods/InvokeProvider.il
@@ -33,6 +33,14 @@
   }
 }
 
+.class interface public abstract auto ansi IReabstractor implements IFoo
+{
+  .method public hidebysig newslot virtual abstract final instance int32 DefaultMethod(int32) cil managed
+  {
+    .override IFoo::DefaultMethod
+  }
+}
+
 .class interface public abstract auto ansi IFoo`1<T>
 {
   .method public hidebysig newslot virtual instance valuetype [mscorlib]System.RuntimeTypeHandle DefaultMethod() cil managed
@@ -67,6 +75,19 @@
   }
 }
 
+.class public auto ansi beforefieldinit Reabstractor
+       extends [mscorlib]System.Object
+       implements IReabstractor
+{
+  .method public hidebysig specialname rtspecialname 
+          instance void .ctor() cil managed
+  {
+    ldarg.0
+    call instance void [mscorlib]System.Object::.ctor()
+    ret
+  }
+}
+
 .class public sequential ansi sealed beforefieldinit ValueFooer
        extends [mscorlib]System.ValueType
        implements IFoo, class IFoo`1<class Fooer>