title: Include MsBuild files in multi-repo solution
body: <p>I would like to add some MsBuild files, which are in different Git repositories, but are always built at the same time, to a common Visual Studio solution. In VS2022, support for multi-repo solutions has been added, which seems like a useful feature for me.</p>
  <p>My MsBuild files are quite simple. They do not compile anything; they only run an external tool or print summaries of item lists.</p>
  <p>I have renamed the extension of my files from <code>.proj</code> to <code>.msbuildproj,</code> since .proj was not an accepted project format in Visual Studio. Still, Visual Studio will not accept my MsBuild files as project files (&quot;cannot be opened by the project system&quot;, &quot;missing some critical imports&quot;).</p>
  <p>What is the recommended project/solution type to go with in this case? What would a valid <code>.msbuildproj</code> file look like?</p>
  <p>Sample MsBuild file:</p>
  <pre><code>&lt;Project ToolsVersion=&quot;4.0&quot; xmlns=&quot;http://schemas.microsoft.com/developer/msbuild/2003&quot; DefaultTargets=&quot;Build&quot;&gt;
    &lt;Import Project=&quot;MyFiles.xml&quot;/&gt;
    &lt;Target Name=&quot;Build&quot; DependsOnTargets=&quot;PrintSourceFiles&quot;/&gt;
    &lt;Target Name=&quot;PrintSourceFiles&quot;&gt;
      &lt;ItemGroup&gt;
        &lt;MyList Include=&quot;@(MyFirstFiles);@(OtherTexts);@(TheRestOfTheFiles)&quot;&gt;&lt;/MyList&gt;
      &lt;/ItemGroup&gt;
      &lt;Message Text=&quot;%(MyList.FullPath)&quot; /&gt;
    &lt;/Target&gt;
  &lt;/Project&gt;
  </code></pre>