Code contract rewrite failing with 'Could not resolve member reference'

Question

Note that this might be a duplicate of this question, I'm not entirely sure.

My problem is that I have a class library project which has a reference to a third-party type library (COM). I want to put contracts into the methods in the class library, like so:

public class foo
{
    public static int divide(TypeFromTypeLib tftl, int a, int b)
    {
        Contract.Requires<ArgumentException>(b != 0);
        return a / b;
    }
}

And then have a client project make use of this method, e.g.

var n = foo.divide(null, 4, 2);

But I'd also like the client project also use contracts in some of its methods. So, I set the Code Contracts properties on both projects to 'Perform Runtime Contract Checking' (without which you get the runtime assert telling you that it needs this setting).

Now, when I then try to compile the client, I get the following error:

Could not resolve member reference: my_class_lib.foo::divide.

ccrewrite : error : Rewrite aborted due to metadata errors.

Which seems unavoidable - any time a method is called which has a type from the third party type library this happens. Remove the type from the method's signature and it's fine.

Can anyone explain why this happens? Is this a clue that the structure of my code is fundamentally flawed (if so, why?), or is it a quirk of code contracts? Is there a recommended fix for this problem?

I am getting this error from ccrewrite, from methods in a 1st party library that have embedded interop types in their signature. — JamesFaix, Feb 29 '16 at 17:42
I had my project open in VS2015 and switched to VS2013 and the issue went away. The Roslyn compiler seems to treat embedded interop types differently than the old compiler, but I can't find any documentation or conversation about it. Possibly related: http://stackoverflow.com/questions/35641972/why-does-visual-studio-2015-throw-more-cs1769-compiler-errors-than-vs2013 — JamesFaix, Mar 01 '16 at 00:00
What version of code contracts do you have installed? Up until the release of v.1.10.10126.2-rc1 on Jan 26, 2016 I've never got runtime checking in code contracts working in Visual Studio 2015. This version is the first major community-driven release of code contracts and addresses a lot of pending issues. It can be downloaded from: https://github.com/Microsoft/CodeContracts/releases. I have it installed and runtime checking now works for me again. — Ɖiamond ǤeezeƦ, Mar 01 '16 at 12:21
I know that the generic and regular versions of `Contract.Requires` are treated differently by `ccrewrite` in that the later can be included in the code even if you do not execute `ccrewrite`. Have you tried replacing `Contract.Requires(b != 0);` with `Contract.Requires(b != 0);` ? — Igor, Mar 07 '16 at 16:39

Michał Komorowski · Answer 1 · 2016-03-02T13:10:15.523

To be honest I don't know why ccrewrite has a problem with interop types but I can give you 3 workarounds:

Solution 1

This one is the simplest:

Go to list of references for a project.
Find third-party type library.
Right click.
From the context menu select Properties.
Change Embed Interop Types from True to False.

You have to do that for both projects. The drawback of this solution is that after a build you will get an additional interop assembly in the bin folder.

Solution 2

Another solution might be to remove types from a third-party type library from a public interface i.e.:

public class foo
{
    public static int divide(int a, int b)
    {
        return divide(null, a, b);
    }

    private static int divide(TypeFromTypeLib tftl, int a, int b)
    {
        Contract.Requires<ArgumentException>(b != 0);
        return a / b;
    }
}

Of course you can do that only if you do not need to use TypeFromTypeLib in your client.

Solution 3

If you need to use TypeFromTypeLib in your client you may write a wrapper for this class i.e.:

public class MyTypeFromTypeLib
{
   //...
}

public class foo
{
    public static int divide(MyTypeFromTypeLib mytftl, int a, int b)
    {
        var tftl = new TypeFromTypeLib();
        //Map MyTypeFromTypeLib  to TypeFromTypeLib 
        //...
        return divide(tftl , a, b);
    }

    private static int divide(TypeFromTypeLib tftl, int a, int b)
    {
        Contract.Requires<ArgumentException>(b != 0);
        return a / b;
    }
}

However, this solution is cumbersome because additional classes are needed.

Code contract rewrite failing with 'Could not resolve member reference'

1 Answers1