Look on base types and interfaces for interfaceImpl

src/tools/illink/src/linker/Linker/InterfaceImplementor.cs

@@ -1,6 +1,9 @@
 // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+using System;
+using System.Collections;
+using System.Collections.Generic;
 using System.Diagnostics;
 using Mono.Cecil;
 
@@ -27,5 +30,39 @@ public InterfaceImplementor (TypeDefinition implementor, InterfaceImplementation
 			InterfaceImplementation = interfaceImplementation;
 			InterfaceType = interfaceType;
 		}
+
+		public static InterfaceImplementor Create(TypeDefinition implementor, TypeDefinition interfaceType, IMetadataResolver resolver)
+		{
+			foreach(InterfaceImplementation iface in implementor.Interfaces) {
+				if (resolver.Resolve(iface.InterfaceType) == interfaceType) {
+					return new InterfaceImplementor(implementor, iface, interfaceType);
+				}
+			}
+			var baseTypeRef = implementor.BaseType;
+			while (baseTypeRef is not null) {
+				var baseType = resolver.Resolve (baseTypeRef);
+				foreach(InterfaceImplementation iface in baseType.Interfaces) {
+					if (resolver.Resolve(iface.InterfaceType) == interfaceType) {
+						return new InterfaceImplementor(implementor, iface, interfaceType);
+					}
+				}
+				baseTypeRef = baseType.BaseType;
+			}
+
+			Queue<TypeDefinition> ifacesToCheck = new ();
+			ifacesToCheck.Enqueue(implementor);
+			while (ifacesToCheck.Count > 0) {
+				var myFace = ifacesToCheck.Dequeue ();
+
+				foreach(InterfaceImplementation ifaceImpl in myFace.Interfaces) {
+					var iface = resolver.Resolve (ifaceImpl.InterfaceType);
+					if (iface == interfaceType) {
+						return new InterfaceImplementor(implementor, ifaceImpl, interfaceType);
+					}
+					ifacesToCheck.Enqueue (iface);
+				}
+			}
+			throw new InvalidOperationException ($"Type '{implementor.FullName}' does not implement interface '{interfaceType.FullName}' directly or through any base types or interfaces");
+		}
 	}
 }

src/tools/illink/src/linker/Linker/TypeMapInfo.cs

@@ -29,9 +29,11 @@
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
 
+using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
+using System.Linq;
 using Mono.Cecil;
 
 namespace Mono.Linker
@@ -222,21 +224,13 @@ void MapOverrides (MethodDefinition method)
 				MethodDefinition? baseMethod = context.TryResolve (baseMethodRef);
 				if (baseMethod == null)
 					continue;
-				if (baseMethod.DeclaringType.IsInterface)
+				if (!baseMethod.DeclaringType.IsInterface)
 				{
-					// Find the matching interface implementation if the base is an interface method
-					foreach (var iface in method.DeclaringType.Interfaces)
-					{
-						if (context.TryResolve (iface.InterfaceType) == baseMethod.DeclaringType)
-						{
-							AnnotateMethods (baseMethod, method, new InterfaceImplementor (method.DeclaringType, iface, baseMethod.DeclaringType));
-							break;
-						}
-					}
+					AnnotateMethods (baseMethod, method);
 				}
 				else
 				{
-					AnnotateMethods (baseMethod, method);
+					AnnotateMethods (baseMethod, method, InterfaceImplementor.Create (method.DeclaringType, baseMethod.DeclaringType, context));
 				}
 			}
 		}