Code model of EnvDTE using Roslyn internally in VS 2015. Bugs ahead.

One of the things that I have done in the last weeks has been to run the integration tests that I have for my MZ-Tools extension (now converted to a package) in Visual Studio 2015 Preview. I have hundreds of them and pass successfully in VS 2005 / 2008 / 2010 / 2012 and 2013 (with some sporadic timing-related failures that I try to reproduce and fix forever, but that’s another subject). When I ran them on VS 2015 Preview, dozens and dozens of them failed, to my desolation, because I immediately knew that there was something very wrong in VS 2015. One after another, I clasified them, identified patterns and all of them were related to the code model (EnvDTE.ProjectItem.FileCodeModel, EnvDTE.CodeElement, etc.) which my add-in uses intensively in several features. Eventually I isolated the root causes and I identified several bugs in the implementation of the automation code model in VS 2015, which soon I learned was changed internally to use the .NET compiler platform (“Roslyn”). I even discovered and disassembled the new assemblies that provide the implementation because one of the bugs is so severe that it crashes Visual Studio:

FatalExecutionEngineError / InvalidCastException after sorting body-less properties in VB.NET file

Although I can reproduce it 100%, I have not isolated it to the minimal package because I think that with the information provided to Microsoft should be enough. I am still awaiting the acknowledgement of the problem.

Other ones, that are far less severe, don’t crash Visual Studio but cause exceptions, and would need some fix:

ComException getting start/end points of EnvDTE80.CodeEvent Adder/Remover/Thrower

EnvDTE.CodeParameter.StartPoint and EndPoint causes exception for “ByVal ParamArray” parameters

EnvDTE.CodeFunction.FunctionKind causes exception for methods of classes with explicit interface implementation

And yet another ones don’t cause exceptions, but return an incorrect value when in VS 2013 returned the correct values:

EnvDTE.CodeElement.FullName doesn’t return full name for constants, fields, methods, properties and events in VB.NET

EnvDTE.CodeClass.Members collection doesn’t include code elements for “Declare” methods of VB.NET class

EnvDTE.CodeFunction.FunctionKind doesn’t return vsCMFunction.vsCMFunctionDestructor for Protected Overrides Sub Finalize()

EnvDTE.CodeFunction.FunctionKind doesn’t return correct value for EnvDTE80.CodeEvent.Adder, Remover or Thrower

EnvDTE.CodeDelegate.Attributes and EnvDTE80.CodeEvent.Attributes returns 0 elements always

This change in the implementation of the automation code model to use “Roslyn” is quite surprising to me. I reported lots of bugs in the automation code model in the last years until I got tired of getting the same answer: no fix would be provided because a new API was being developed. Later I learned that the new API was Roslyn but I didn’t expect the automation code model bugs to be fixed by leveraging Roslyn. AFAIK, Microsoft hasn’t provide any information about this change, but the truth is that bugs have been introduced. I have implemented workarounds in my code for some of them until Microsoft fixes them (in VS 2015 CTP5 they are not fixed). There are also a couple of them (very minor) that I haven’t reported yet. So, if your extension uses the automation code model, I encourage you to test that area carefully and report the bugs that you find.

3 thoughts on “Code model of EnvDTE using Roslyn internally in VS 2015. Bugs ahead.”

  1. Hi Carlos —

    Yes, we had to re-implement C# and Visual Basic’s Code Model implementations on top of Roslyn. The situation is that the Code Model is actually exposed by the language services — it isn’t separate a thing. Because we have completely rebuilt the C# and Visual Basic language services for Visual Studio 2015, Code Model had to be rebuilt as well.

    Thanks very much for your bug reports. We put out a lot of previews of Roslyn over the past year or so to try and shake out many of these problems, but we’re still getting to the end of the tail of bugs. I was actually the one who drew the short straw and rebuilt C# and VB Code Model, so the bugs are mine. 🙂

    If you find more problems, please let us know right away. Also, if you want to report issues to us more expediently, you can do so over at

    Dustin Campbell
    Visual Studio Managed Languages

  2. If possible, I would like Microsoft to offer a session(s) at Build 2015 that explain vNext VS extensions, VS Shell, new capabilities and issues introduced. Carlos, use your connections to help make this happen 🙂

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