VisualStudioTextTransform

The Problem:

Basically we want to transform our T4 templates as part of the build, but still use the "Host" variable. A stackoverflow answer reveals that this is not possible out-of-the-box: http://stackoverflow.com/questions/14409368/t4-template-will-not-transform-with-build/14409896#14409896

However there is possible to write a custom TextTransform.exe in a way to provide the necessary services to the T4 templates.

The Solution

The Technologies

Custom TextTransform.exe.

You can actually create a modified template host with by implementing the ITextTemplatingEngineHost interface.

• https://msdn.microsoft.com/en-us/library/bb126519.aspx
• https://msdn.microsoft.com/en-us/library/microsoft.visualstudio.texttemplating.itexttemplatingenginehost%28v=vs.110%29.aspx

EnvDTE.DTE interface.

Some text templates use the "Automation and Extensibility for Visual Studio"-API (EnvDTE.DTE interface). So in order to use those templates you need to provide the DTE interface from within your custom host as well. To provide a DTE instance to the template we obviously need to either create an instance or get one from an existing Visual Studio instance.

• http://www.viva64.com/en/b/0169/
• https://msdn.microsoft.com/en-us/library/envdte.dte.aspx

Combining the technologies

We can now combine the two technologies to write a custom text template processor, which provides exactly the same behavior as the Visual Studio Text template processor.

First we create a custom T4 template host and implement the ITextTemplatingEngineHost interface almost exactly as given by the Microsoft sample above. The differences are:

• We additionally implement IServiceProvider to provide the EnvDTE80.DTE2/EnvDTE.DTE instance
• We replace $(ProjectDir) and $(TargetDir) with the respective paths (read from the dte instance), because some of our text templates expected those paths.

We use the same MessageFilter class as suggested by http://www.viva64.com/en/b/0169/ to automatically retry on COMExceptions.

Finally we create our own EnvDTE.DTE instance, iterate over all text template files and process them with our new shiny host.

You can find an example implementation in this repository.

Usage

./VisualStudioTextTransform.exe <solution-file> (--TargetDir <target-dir>)

This will transform all the *.tt files from the given solution (The tool is searching all sub-directories). You can optionally specify a target-dir if you use $(TargetDir) in your templates and overwrite the location via msbuild command line.

Known Limitations

• The program will “hang” when Visual Studio decides to open a startup dialog (for example: License, ReSharper, …). It’s a good idea to manually open Visual Studio (and check that no dialog pops up) before using this program.