`ArgumentException`: "Could not find method overriding method" with overridden class method having generic by-ref parameter about core HOT 3 CLOSED

Thanks for reporting this @rbeurskens. Don't worry about your repro code example making use of NSubstitute for now, I expect it shouldn't be too difficult figuring out the underlying calls and deriving DynamicProxy-only repro code.

from core.

OK, it's taken me a while, but here is a corresponding DynamicProxy-only repro code example:

var generator = new ProxyGenerator();
var factory = generator.CreateClassProxy<DerivedFactory>(new QueryMethodInvocationTargetInterceptor());
factory.Create<object>(out _);

class QueryMethodInvocationTargetInterceptor : IInterceptor
{
    public void Intercept(IInvocation invocation)
    {
        _ = invocation.MethodInvocationTarget;
    }
}

public interface IFactory  // NOTE: the issue is also reproducible without this interface
{
    void Create<T>(out T result);
}

public class Factory : IFactory
{
    public virtual void Create<T>(out T result) => result = default;
}

public class DerivedFactory : Factory
{
    public override void Create<T>(out T result) => result = default;
}

It seems that the error is caused in this method:

When given two matching generic types (or type parameters) by-ref (in our repro code: the out T result parameters' types), this method claims that they do not match. This could possibly be fixed by introducing some new logic that erases by-ref-ness for further comparisons:

 private bool EqualSignatureTypes(Type x, Type y)
 {
     if (x.IsGenericParameter != y.IsGenericParameter)
     {
         return false;
     }
     else if (x.IsGenericType != y.IsGenericType)
     {
         return false;
     }
 
+    if (x.IsByRef != y.IsByRef)
+    {
+        return false;
+    }
+
+    if (x.IsByRef)
+    {
+        x = x.GetElementType();
+        y = y.GetElementType();
+    }
+
     if (x.IsGenericParameter)
     ...

But I haven't checked yet whether this code breaks any existing test cases.

The suggested code addition does not appear to break any existing test cases, but we should still double-check its validity, and whether it can possibly be added in a more optimal place (from a run-time performance standpoint).

from core.

Scratch the code fix suggested above, the following would be more correct (because it doesn't skip the first two checks):

 private bool EqualSignatureTypes(Type x, Type y)
 {
+    if (x.IsByRef != y.IsByRef)
+    {
+        return false;
+    }
+    else if (x.IsByRef)
+    {
+        return EqualSignatureTypes(x.GetElementType(), y.GetElementType());
+    }
+
     if (x.IsGenericParameter != y.IsGenericParameter)
     ...

from core.