T4 Text Transformations in VS2013 and VS2015

Question

Our company has legacy system that heavily relies on T4 and the employee who architected it is gone. It was running fine for us, however recently some developers upgraded to VS2015. The T4 transformations stopped working for them (with error similar as reported below). It looked at though there were references to Microsoft.VisualStudio.TextTemplating.12.0.dll. They changed the references to '14' and all worked for them. However, the same project shared by other developers on VS2013 no longer worked with error:

Compiling transformation: The type 'Microsoft.VisualStudio.TextTemplating.TextTransformation' is defined in an assembly that is not referenced. You must add a reference to assembly 'Microsoft.VisualStudio.TextTemplating.14.0, Version=14.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.

Are you able to run T4 on same project that is opened in both VS2013 and VS2015? One side note, there was a dependent assembly that the old employee made that all the TextTransformations derived from (it also provides helpers that are used in the *.tt files). Unfortunately it used an interface only present in Microsoft.VisualStudio.TextTemplating.Interfaces.10.0.dll, so that old reference is being dragged aroundÎ. Not sure if that is contributing or not. But basically here is the bottom line:

When all devs on VS2013, everything worked and references were:

Microsoft.VisualStudio.TextTemplating.12.0.dll
Microsoft.VisualStudio.TextTemplating.Interfaces.10.0.dll
Microsoft.VisualStudio.TextTemplating.VSHost.12.0.dll

Then when some went to vs2015, the only way to get it to work was to change out the 12.0* dlls with 14.0, but then vs2013 developers ceased to work.

UPDATE

I might not have clarified our complete setup. We have 20-30 *.tt files in a separate project that is included in the solution with the project that will have Text Transformations applied to it.

1. We have a helper Extensibility.CodeGeneration.dll (this references Microsoft.VisualStudio.TextTemplating.N.dll files as well) that have several static helpers and also base classes that derive from Microsoft.VisualStudio.TextTemplating.TextTransformation.

2. The 'templates' project that contains all the *.tt files, every .tt file use static methods from our helper dll. It also references all the same Microsoft.VisualStudio. dlls.

3. In every *.tt file, we have something that looks like this, where AreaTemplate is a class defined in the *.tt file itself and either derives from Microsoft.VisualStudio.TextTemplating.TextTransformation or one of the exposed base classes in our helper dll.

   var template = new AreaTemplate { Settings = settings, Area = area, Layouts = layouts }; Write( template.TransformText() );

4. It was asked in comments how I obtained/used a 'host'. In searching through code we have a few common scenarios (all done inside the helper dll). In each instance, host is of type ITextTemplatingEngineHost.

Case 1:

var dte = (EnvDTE.DTE)( (IServiceProvider)host ).GetService( typeof( EnvDTE.DTE ) );

Case 2:

var hostServiceProvider = (IServiceProvider)host;

Given #3 above, I think I have to reference the Microsoft.TextTemplating dlls (and not just the Interfaces dll) due to the use/exposing of TextTransformation class.

Also, if I change references to in both my 'Helper' and 'Templates' project to 12.0...in vs2015, I get error about 'you must add reference to 12.0'...I have references to that in both applicable (in my eyes) projects...not sure why VS tells me to add it. I tried adding an explicit reference in the *.tt file using

<#@ assembly Name="$(ProjectDir)..\..\Assemblies\Microsoft.VisualStudio.TextTemplating.12.0.dll" #>

But then I got the error

The type 'Microsoft.VisualStudio.TextTemplating.TextTransformation' exists in both 'c:\BTR\Source\Assemblies\Microsoft.VisualStudio.TextTemplating.12.0.dll' and 'c:\Windows\Microsoft.NET\assembly\GAC_MSIL\Microsoft.VisualStudio.TextTemplating.14.0\v4.0_14.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualStudio.TextTemplating.14.0.dll'

It is almost like there is a hidden/implicit reference to the latest Texttemplating already built into VS??

Not sure if our setup was a more complicated way to achieve our original goal, but I don't think I'll be able to unwind it and change if we are doing it the incorrect way.

Given our setup let me know if you think I am stuck or not. I was trying to figure out 'conditions' in MSBuild to help support both Visual Studios but couldn't succeed.

Thanks in advance.

Answer 1

I have faced the same problem and I think I have a solution, which works - use the VisualStudioVersion msbuild property to reference the right version of the assemblies. Something like this:

<Reference Include="Microsoft.VisualStudio.TextTemplating.$(VisualStudioVersion)">
  <HintPath>..\Dependencies\Microsoft.VisualStudio.TextTemplating.$(VisualStudioVersion).dll</HintPath>
</Reference>
<Reference Include="Microsoft.VisualStudio.TextTemplating.Interfaces.10.0">
  <HintPath>..\Dependencies\Microsoft.VisualStudio.TextTemplating.Interfaces.10.0.dll</HintPath>
</Reference>

Make sure the Dependencies folder has both Microsoft.VisualStudio.TextTemplating.12.0.dll and Microsoft.VisualStudio.TextTemplating.14.0.dll.

Seems to work.

Answer 2

We have a very similar scenario to yours, just a bit more complex because our T4 templates depend on a couple of DSL-Tools packages.

I’ve made some tests and in fact the solution for this problem is to remove any reference to Microsoft.VisualStudio.TextTemplating.12.0 and keep the references to the Interfaces assemblies. Exactly as pointed by Frank. This would make the projects and the templates compatible with both Visual Studio 2013 and 2015.

Unfortunately this doesn’t help in our scenario because DSL-tools projects require references to Microsoft.VisualStudio.TextTemplating.12.0 or Microsoft.VisualStudio.TextTemplating.14.0 because the DirectiveProcessor.tt template generates a class that derives from RequiresProvidesDirectiveProcessor, an abstract class that resides in one of those assemblies (depending on the version of Visual Studio you would want to compile the DSL-tools project with). I suppose that is one of the reasons why DSL-tools projects are upgraded when you open them with higher Visual Studio versions… But that is a pain because it forces large teams like ours to upgrade Visual Studio all at the same time.

Answer 3

Try changing the reference from "Microsoft.VisualStudio.TextTemplating.12.0.dll" to "Microsoft.VisualStudio.TextTemplating.Interfaces.12.0.dll". Each new version of Visual Studio services will have a new implementation assembly that will implement the previous versions interfaces. To maintain backward compatibility, you should only reference the interface assemblies and not the implementation assemblies. You might have to change the templates if they reference anything not in the interface.

Updated

Wow, so you have a pretty complicated setup and I don't know if you will be able to use it in both versions without changing the code like you did.

I think the main problem is in your helper class, in #3 you said that the AreaTemplate class derives from TextTransformation. TextTransformation is in the implementation dll so it will exist in each version of visual studio. If you helper dll is complied to reference it from 2013 and then you use that dll in 2015 it will not work.

When a T4 template is transformed, the text in the file is parsed into a class, that class is loaded into an app domain(separate from the one visual studio is running in) and the class's TransformText method is called. Since your templates reference your helper class, the helper assembly will be loaded into the new app domain, which will in turn try to load TextTemplating 12 in there too, the app domain will not be able to resolve the 12 reference because you are using VS 2015.

In the other direction when you reference text templating 14 from 2015 and try to use it in VS 2013 you will have the same problem, the app domain will not be able to find TextTemplating 14 because you are in VS 2013 and the 14 dll does not exist.

In the last scenario when you are in VS 2015 and your add a link to TextTemplating 12 in your tt files it is failing because the app domain created to run the template has already loaded the TextTemplating 14 dll then you also tell it to load the TextTemplating 12 dll. This goes back to my posts in the comments when I talked about VS backward compatibility, TextTemplating 12 and 14 have the same TextTransformation class in the same namespace and the runtime can't load them both so you get that error.

Few things you can try:

1) Put the TextTemplating 12 dll in the GAC on the VS 2015 machines. In theory, this will let the T4 AppDomain load both copies of TextTemplating and then VS 2015 would be able to use the 14 version while your tt files and helper dll use the 12 version. Leave the VS 2013 machines the same.

2) Do the same as 1 but in reverse, setup the projects to target 2015 and reference the 14 dll then on the vs 2013 machines GAC the 14 dll, not sure if this will work since the 14 dll might have other dependencies on newer vs assemblies.

3) On the vs 2015 machines figure out a way to do binding redirects for the T4 App Domain so that calls looking to TextTemplating 12 would be resolved to TextTemplating 14. Usually binding redirects are done in the app/web.config files but not sure how you would do them for T4, may have to peek at the code and see how the app domain is created and loaded.