T4 Text Templating with .NET 8

The software in this repository allows you to run a T4 template with the .NET 8 runtime. This means you can load .NET Core and .NET 5/6/7/8 assemblies and use .NET 8 libraries. My team uses it to generate C# code for types in a .NET assembly (using Reflection). We also use it to process a JSON file using .NET's System.Text.Json library.

Author: RdJNL

Latest release

Version 1.3.0 can be downloaded here.

Requirements

• .NET 8
• .NET Framework 4.8
• Visual Studio 2019/2022 (for the VS extension)

How to use it

Visual Studio 2019/2022 extension

• The extension is provided as a VSIX file. Run this file to install the extension to Visual Studio. You may need to use an elevated command prompt to run the file as admin.
• Once the extension is installed, open your solution in Visual Studio.
• Select the .tt file in the Solution Explorer, right click it and click properties.
• In the properties window, set Custom Tool to TextTemplatingFileGeneratorCore.
• Right click the file in the Solution Explorer and click Run Custom Tool.

TextTransformCore executable

To use the executable, simply run it from the command line. Provide as first and only argument the path to the template file. If the path has spaces in it, makes sure to surround it with double quotes (").

Differences with Visual Studio's .NET Framework T4 processor

There are several limitations to this approach:

• The hostspecific setting must be false.
• No debugging.
• No template parameters.
• The VS extension cannot be used in database projects (this seems to be a bug in Visual Studio).

This processor has one feature that Visual Studio's processor does not have:

• From a T4 template, you can access the TemplateFile string property to get the absolute path to the template file.

There is one other difference with Visual Studio's processor:

• When running a template using the VS extension, relative paths in assembly directives are relative to the T4 template file, rather than to the solution directory. To provide a path relative to the solution directory, use the $(SolutionDir) environment variable.

Remarks

• Microsoft has added a new T4 command line tool to Visual Studio 2022. See this blog post for more information. The reactions to this tool have been mixed. Hopefully Microsoft's tool will be able to replace this project in the future.
• When using this extension, if you need the T4 template to have access to internal types/members of your assembly, add <ItemGroup><InternalsVisibleTo Include="GeneratedTemplate.dll" /></ItemGroup> to the project file of the assembly containing the internal types/members.

How does it work?

The following steps are followed to process the T4 template:

• .NET Framework 4.8 code (either the VS extension or the TextTransformCore executable) uses Visual Studio's T4 template processor to preprocess the template into C# code. This C# code is saved to a temporary file.
• The .NET Framework code runs a .NET 8 executable which compiles the C# code and runs it. The result is once again saved to a temporary file.
• The .NET Framework code loads the content of the temporary file and either passes it to Visual Studio (the VS extension) or saves it to the output file (the TextTransformCore executable).

License

The license for all contents of the repository can be found in the LICENSE file.