`DynamicProxyException` ("duplicate element") when type to proxy contains members whose names differ only in case

[dark-dark-darkness]

Description

When mocking an interface that contains multiple methods with similar signatures using Moq, an exception is thrown during proxy generation. This issue arises because the proxy generator performs a case-insensitive comparison when determining if methods are duplicates, leading to a conflict even when method names differ only by case.

Moq version: 4.20.72
Castle.Core: 5.1.1
.Net version: net48;net8.0

Program.cs

using Moq;

_ = new Mock<IDialogService>().Object;


public interface IDialogService
{
    bool? YESNoCancel(string? message, Exception? exception);
    bool? YesNOCancel(string? message, Exception? exception);
    bool? YesNoCANCEL(string? message, Exception? exception);
}

Exception

The exception message is as follows:

Castle.DynamicProxy.DynamicProxyException: Duplicate element: Castle.DynamicProxy.Generators.MetaMethod
   at Castle.DynamicProxy.Generators.MetaTypeElementCollection`1.Add(TElement item)
   at Castle.DynamicProxy.Generators.MetaType.AddMethod(MetaMethod method)
   at Castle.DynamicProxy.Contributors.CompositeTypeContributor.MembersCollectorSink.Add(MetaMethod method)
   at Castle.DynamicProxy.Contributors.MembersCollector.<CollectMembersToProxy>g__AddMethod|7_5(MethodInfo method, Boolean isStandalone, <>c__DisplayClass7_0&)
   at Castle.DynamicProxy.Contributors.MembersCollector.<CollectMembersToProxy>g__CollectMethods|7_2(<>c__DisplayClass7_0&)
   at Castle.DynamicProxy.Contributors.MembersCollector.CollectMembersToProxy(IProxyGenerationHook hook, IMembersCollectorSink sink)
   at Castle.DynamicProxy.Contributors.CompositeTypeContributor.CollectElementsToProxy(IProxyGenerationHook hook, MetaType model)
   at Castle.DynamicProxy.Generators.BaseInterfaceProxyGenerator.GenerateType(String typeName, INamingScope namingScope)
   at Castle.DynamicProxy.Generators.BaseProxyGenerator.<>c__DisplayClass13_0.<GetProxyType>b__0(CacheKey cacheKey)
   at Castle.Core.Internal.SynchronizedDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at Castle.DynamicProxy.Generators.BaseProxyGenerator.GetProxyType()
   at Castle.DynamicProxy.DefaultProxyBuilder.CreateInterfaceProxyTypeWithoutTarget(Type interfaceToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options)
   at Castle.DynamicProxy.ProxyGenerator.CreateInterfaceProxyTypeWithoutTarget(Type interfaceToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options)
   at Castle.DynamicProxy.ProxyGenerator.CreateInterfaceProxyWithoutTarget(Type interfaceToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options, IInterceptor[] interceptors)
   at Moq.CastleProxyFactory.CreateProxy(Type mockType, IInterceptor interceptor, Type[] interfaces, Object[] arguments) in /_/src/Moq/Interception/CastleProxyFactory.cs:line 50
   at Moq.Mock`1.InitializeInstance() in /_/src/Moq/Mock`1.cs:line 309
   at Moq.Mock`1.OnGetObject() in /_/src/Moq/Mock`1.cs:line 323
   at Moq.Mock.get_Object() in /_/src/Moq/Mock.cs:line 181
   at Moq.Mock`1.get_Object() in /_/src/Moq/Mock`1.cs:line 281
   at Program.<Main>$(String[] args) in D:\repos\ConsoleApp2\ConsoleApp2\Program.cs:line 3

[stakx]

Thanks for reporting this, @dark-dark-darkness.

This is caused by the case-insensitive method name comparison here:

Core/src/Castle.Core/DynamicProxy/Generators/MetaMethod.cs

Line 72 in 8411ea6

if (!StringComparer.OrdinalIgnoreCase.Equals(name, other.name))

which was introduced a long time ago, in d1d6226.

I'm not sure why StringComparer.OrdinalIgnoreCase was chosen over StringComparer.Ordinal – perhaps in consideration of case-insensitive languages like VB.NET or the CLS (Common Language Specification)?

In any case, I tried changing the above line of code to use StringComparer.Ordinal instead, which broke no tests and fixed the above scenario. So we could probably classify this as a bug, and go ahead and make the method name comparisons case-insensitive.

Any thoughts?