MEF and open generics using ConventionBuilder

[TMiNus]

I am trying to use MEF with open generics without markups attributes, this is an example of the problem

public class Logger<TLog>
{
      private ISetting settings;

      public Logger(ISetting settings)
      {
          this.settings = settings;
      }

      public TLog Fetch()
      {
          return default(TLog);
      }
}

To create the container I do

var conventions = new ConventionBuilder();

conventions.ForType<Setting>()
           .Export<ISetting>();
conventions.ForType(typeof(Logger<>))
           .Export();

var configuration = new ContainerConfiguration()
      .WithAssembly(typeof(Program).Assembly, conventions);

using (var container = configuration.CreateContainer())
{
       var logic = container.GetExport(typeof(Logger<object>));
}

With that code I am getting a No importing constructor was found on type 'Logger`1[System.Object]' exception

If I mark the constructor with the attribute it works as intended but this should be possible without using markups

I have also tried this on the MEF version that ships with .NET40 and it works without the markups

My findings about the issue

[TMiNus]

I think I got the bug solved, unit test enhanced. Sorry for the commit with the short message, fixed that :)

[nblumhardt]

SelectConstructor() should cover this scenario:

conventions.ForType(typeof(Logger<>))
    .SelectConstructor(c => c.Single())
    .Export();

But, as you've pointed out, it's not working here. The delegate is invoked with the list of constructors from Logger<>, but the returned value isn't being applied when constructors from Logger<object> are searched. This looks like a bug.

[TMiNus]

I already found the source of the problem for the SelectConstructor although the fix would require a little more work.

To be honest the problem is not rooted in SelectConstructor it derives from the open closed generics.

[karelz]

@TMiNus do you have a fix? We would be happy to take it ...

[karelz]

I assume it was fixed by dotnet/corefx#15315.

[danielmeza]

I have this bug, I'm using System.Composition v 1.2 in a netcopreapp2.1

[karelz]

@danielmeza it was supposed to be fixed in 2.0.
Please create minimal repro and file a new issue if you think something is still left.