Exclude explicitly implemented interface methods from proxy (#8992)

* Exclude ExplicitInterfaceImplementation methods

* Add comments to test types and rename to suit

---------

Co-authored-by: ReubenBond <rebond@microsoft.com>

src/Orleans.CodeGenerator/Model/ProxyInterfaceDescription.cs

@@ -79,6 +79,14 @@ private List<ProxyMethodDescription> GetMethods()
             {
                 foreach (var method in iface.GetDeclaredInstanceMembers<IMethodSymbol>())
                 {
+                    if (method.MethodKind == MethodKind.ExplicitInterfaceImplementation)
+                    {
+                        // Explicit implementations can be ignored when generating a proxy.
+                        // Proxies must implement every method explicitly to ensure faithful reproduction of the interface behavior.
+                        // At the calling side, the explicit implementation will be called if it was not overridden by a derived type.
+                        continue;
+                    }
+
                     var methodDescription = CodeGenerator.GetProxyMethodDescription(InterfaceType, method: method);
                     result.Add(methodDescription);
                 }

test/DefaultCluster.Tests/CodeGenTests/IRuntimeCodeGenGrain.cs

@@ -8,6 +8,31 @@ namespace Tester.CodeGenTests
     using Orleans;
     using Orleans.Providers;
 
+    // Regression test for explicit interface method implementations https://github.com/dotnet/orleans/issues/8991
+    public interface IExplicitInterfaceMethodImplementationTestGenericBase<in T>
+    {
+        Task M(T arg);
+    }
+
+    public interface IExplicitInterfaceMethodImplementationTestBase : IExplicitInterfaceMethodImplementationTestGenericBase<object>;
+
+    public interface IExplicitInterfaceMethodImplementationTestDerived : IExplicitInterfaceMethodImplementationTestBase, IExplicitInterfaceMethodImplementationTestGenericBase<string>
+    {
+        Task IExplicitInterfaceMethodImplementationTestGenericBase<object>.M(object obj) => M(obj);
+    }
+
+    public interface IExplicitInterfaceMethodImplementationTestImplementation : IExplicitInterfaceMethodImplementationTestDerived, IGrainWithGuidKey;
+
+    public class ExplicitInterfaceMethodImplementationTestGrain : Grain, IExplicitInterfaceMethodImplementationTestImplementation
+    {
+        public Task M(string arg)
+        {
+            throw new NotImplementedException();
+        }
+    }
+
+    // End regression test for https://github.com/dotnet/orleans/issues/8991
+
     public interface IGrainWithGenericMethods : IGrainWithGuidKey
     {
         Task<Type[]> GetTypesExplicit<T, U, V>();