Using T4 templates to manage assembly version information

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I wanted to configure version information generation for some .NET projects. It’s been a long time since I investigated available options, so I searched around hoping to find some simple way of doing this. What I’ve found didn’t look very encouraging: people write Visual Studio add-ins and custom MsBuild tasks just to obtain one integer number (okay, maybe two). This felt overkill for a small personal project.

The inspiration came from one of the StackOverflow discussions where somebody suggested that T4 templates could do the job. And of course they can. The solution requires a minimal effort and no Visual Studio or build process customization. Here what should be done:

1. Create a file with extension ".tt" and place there T4 template that will generate AssemblyVersion and AssemblyFileVersion attributes:

<#@ template language="C#" #>
// 
// This code was generated by a tool. Any changes made manually will be lost
// the next time this code is regenerated.
// 

using System.Reflection;

[assembly: AssemblyVersion("1.0.1.<#= this.RevisionNumber #>")]
[assembly: AssemblyFileVersion("1.0.1.<#= this.RevisionNumber #>")]
<#+
    int RevisionNumber = (int)(DateTime.UtcNow - new DateTime(2010,1,1)).TotalDays;
#>

You will have to decide about version number generation algoritm. For me it was sufficient to auto-generate a revision number that is set to the number of days since January 1st, 2010. As you can see, the version generation rule is written in plain C#, so you can easily adjust it to your needs.

2. The file above should be placed in one of the projects. I created a new project with just this single file to make version management technique clear. When I build this project (actually I don’t even need to build it: saving the file is enough to trigger a Visual Studio action), the following C# is generated:

// 
// This code was generated by a tool. Any changes made manually will be lost
// the next time this code is regenerated.
// 

using System.Reflection;

[assembly: AssemblyVersion("1.0.1.113")]
[assembly: AssemblyFileVersion("1.0.1.113")]

Yes, today it’s 113 days since January 1st, 2010. Tomorrow the revision number will change.

3. Next step is to remove AssemblyVersion and AssemblyFileVersion attributes from AssemblyInfo.cs files in all projects that should share the same auto-generated version information. Instead choose “Add existing item” for each projects, navigate to the folder with T4 template file, select corresponding “.cs” file and add it as a link. That will do!

What I like about this approach is that it is lightweight (no custom MsBuild tasks), and auto-generated version information is not added to source control. And of course using C# for version generation algorithm opens for algorithms of any complexity.

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