Lots of build warnings when COM objects ActiveDs or MSXML2 are referenced

After moving a project from .NET 1.1 to .NET 2.0, MsBuild emits lots of warnings for some COM objects.

Sample code for test (actual code doesn't matter, just used to create the warnings):

using System;
using System.DirectoryServices;
using ActiveDs;
namespace Test
{
    public class Class1
    {
        public static void Main(string[] args)
        {
            string adsPath = String.Format("WinNT://{0}/{1}", args[0], args[1]);
            DirectoryEntry localuser = new DirectoryEntry(adsPath);
            IADsUser pUser = (IADsUser) localuser.NativeObject;
            Console.WriteLine("User = {0}", pUser.ADsPath);
        }
    }
}

Warning messages look like

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Microsoft.Common.targets : warning : At least one of the arguments for 'ITypeLib.RemoteGetLibAttr' cannot be marshaled by the runtime marshaler. Such arguments will therefore be passed as a pointer and may require unsafe code to manipulate.

Observations:

Happens for ActiveDs (11 warnings) and MSXML2 (54 warnings).
Not seen for our own COM objects.
<Reference> entry in .csproj file contains attribute WrapperTool = "tlbimp"
Despite of all warnings, no problems have been observed in the running system.

Any idea how to get rid of the warnings?

Solution

According to a comment in the MDSN article about TLBIMP for 2.0, you can't fix this problem w/o running TLBIMP yourself.

It was easy to reproduce your problem using VS. I also reproduced it running TLBIMP manually from a VS comment prompt:

   tlbimp c:\WINNT\system32\activeds.tlb /out:interop.activeds.dll

The fix was to use the /silent switch

   tlbimp c:\WINNT\system32\activeds.tlb /silent /out:interop.activeds.dll

As pointed out in the comment in the MSDN article, the COM reference becomes a .net assembly reference to the interop assembly you built yourself.

I'm not a VS expert, but I made this work by adding a prebuild to project of:

    "$(DevEnvDir)\..\..\SDK\v2.0\bin\tlbimp" c:\WINNT\system32\activeds.tlb
            /namespace:ActiveDs /silent /out:"$(ProjectDir)interop.activeds.dll"

Built it once so I'd have a dll to add a reference with the browse tab. Added a reference to the interop.activeds.dll in my project root and then built again. You may want to do this some other way, like with an external make file via a C++ project. This is more of a POC.

Note a funny difference in MSBUILD vs VS, $(DevEnvDir) has a trailing backslash but MSBUILD does not.