Avoid unneeded custom invocation types on interface proxy w/o target

src/Castle.Core/DynamicProxy/Contributors/InterfaceProxyWithoutTargetContributor.cs

@@ -20,6 +20,7 @@ namespace Castle.DynamicProxy.Contributors
 
 	using Castle.DynamicProxy.Generators;
 	using Castle.DynamicProxy.Generators.Emitters;
+	using Castle.DynamicProxy.Internal;
 
 	internal class InterfaceProxyWithoutTargetContributor : CompositeTypeContributor
 	{
@@ -60,6 +61,15 @@ protected override MethodGenerator GetMethodGenerator(MetaMethod method, ClassEm
 
 		private Type GetInvocationType(MetaMethod method, ClassEmitter emitter)
 		{
+			var methodInfo = method.Method;
+
+			if (canChangeTarget == false && methodInfo.IsAbstract && methodInfo.IsGenericMethod == false && methodInfo.IsGenericMethodDefinition == false)
+			{
+				// We do not need to generate a custom invocation type because no custom implementation
+				// for `InvokeMethodOnTarget` will be needed (proceeding to target isn't possible here):
+				return typeof(InterfaceMethodWithoutTargetInvocation);
+			}
+
 			var scope = emitter.ModuleScope;
 			Type[] invocationInterfaces;
 			if (canChangeTarget)
@@ -70,14 +80,14 @@ private Type GetInvocationType(MetaMethod method, ClassEmitter emitter)
 			{
 				invocationInterfaces = new[] { typeof(IInvocation) };
 			}
-			var key = new CacheKey(method.Method, CompositionInvocationTypeGenerator.BaseType, invocationInterfaces, null);
+			var key = new CacheKey(methodInfo, CompositionInvocationTypeGenerator.BaseType, invocationInterfaces, null);
 
 			// no locking required as we're already within a lock
 
 			return scope.TypeCache.GetOrAddWithoutTakingLock(key, _ =>
-				new CompositionInvocationTypeGenerator(method.Method.DeclaringType,
+				new CompositionInvocationTypeGenerator(methodInfo.DeclaringType,
 				                                       method,
-				                                       method.Method,
+				                                       methodInfo,
 				                                       canChangeTarget,
 				                                       null)
 				.Generate(emitter, namingScope)

src/Castle.Core/DynamicProxy/Internal/InterfaceMethodWithoutTargetInvocation.cs

@@ -0,0 +1,61 @@
+// Copyright 2004-2021 Castle Project - http://www.castleproject.org/
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+namespace Castle.DynamicProxy.Internal
+{
+	using System;
+	using System.ComponentModel;
+	using System.Diagnostics;
+	using System.Reflection;
+
+#if FEATURE_SERIALIZATION
+	[Serializable]
+#endif
+	[EditorBrowsable(EditorBrowsableState.Never)]
+	public sealed class InterfaceMethodWithoutTargetInvocation : AbstractInvocation
+	{
+		public InterfaceMethodWithoutTargetInvocation(object target, object proxy, IInterceptor[] interceptors, MethodInfo proxiedMethod, object[] arguments)
+			: base(proxy, interceptors, proxiedMethod, arguments)
+		{
+			// This invocation type is suitable for interface method invocations that cannot proceed
+			// to a target, i.e. where `InvokeMethodOnTarget` will always throw:
+
+			Debug.Assert(target == null, $"{nameof(InterfaceMethodWithoutTargetInvocation)} does not support targets.");
+			Debug.Assert(proxiedMethod.IsAbstract, $"{nameof(InterfaceMethodWithoutTargetInvocation)} does not support non-abstract methods.");
+
+			// Why this restriction? Because it greatly benefits proxy type generation performance.
+			//
+			// For invocations that can proceed to a target, `InvokeMethodOnTarget`'s implementation
+			// depends on the target method's signature. Because of this, DynamicProxy needs to
+			// dynamically generate a separate invocation type per such method. Type generation is
+			// always expensive... that is, slow.
+			//
+			// However, if it is known that `InvokeMethodOnTarget` won't forward, but throw,
+			// no custom (dynamically generated) invocation type is needed at all, and we can use
+			// this unspecific invocation type instead.
+		}
+
+		// The next three properties mimick the behavior seen with an interface proxy without target.
+		// (This is why this type's name starts with `Interface`.) A similar type could be written
+		// for class proxies without target, but the values returned here would be different.
+
+		public override object InvocationTarget => null;
+
+		public override MethodInfo MethodInvocationTarget => null;
+
+		public override Type TargetType => null;
+
+		protected override void InvokeMethodOnTarget() => ThrowOnNoTarget();
+	}
+}