Setting a breakpoint in a T4 template

Question

I'm trying to debug the execution of a T4 template in Visual Studio 2008.

All the information I'm finding on debugging T4 templates in Visual Studio 2008 say that you can set a breakpoint (red dot) in the template as if it were a regular code file. I have the Clarius T4 code highlighter installed, so my T4 template is colored, but I can't set a breakpoint. When I click in the margin nothing happens.

I've tried Debugger.Break(), and it launches a new instance of VS.NET, but it can't load the code from my template. I get a dialog that says "There is no source code available for the current location." This happens if I have the same project loaded in the another instance of if I spin up a new instance.

What gives?

Answer 1

Set the following:

<#@ template debug="true" hostSpecific="true" #>
<#@ import namespace="System.Diagnostics" #>

Then in your template

Debugger.Launch();

VS will kick off the JIT debugger in a new instance of VS 2010

Answer 2

In Visual Studio 2013:

1. Set a breakpoint in the .tt file
2. Right-click the .tt file in the solution explorer
3. Select "Debug T4 Template"
4. Done!

No attaching a second instance of Visual Studio needed.