Including Generated Files Into Your Build

Files generated during the build are generally ignored by the build process. This can lead to confusing results, such as generated files not being included in the output directory by default. This article aims to explain why.

Static vs. Generated files

Files that get generated during the build behave differently from static files (eg. source files). For this reason, it's important to understand How MSBuild Builds Projects. I'll cover the main two phases here at a high level.

Evaluation Phase

MSBuild reads your project, imports everything, creates Properties, expands globs for Items outside of Targets, and sets up the build process.

Execution Phase

MSBuild runs Targets & Tasks with the provided Properties & Items in order to perform the build.

Key Takeaway: Files generated during execution don't exist during evaluation, therefore they aren't found. This particularly effects files that are globbed by default, such as source files (.cs).

The solution? When the files are generated, manually add them into the build process. The recommended way to do this is by adding the new file to the Content or None items before the BeforeBuild target.

Here's a sample target that does this:

<Target Name="Foo" BeforeTargets="BeforeBuild">
  
  <!-- Some logic that generates your file goes here -->
  <!-- Note: We recommend generating your files into $(IntermediateOutputPath)   -->

  <ItemGroup>
    <!-- If your generated file was placed in `obj\` -->
    <None Include="$(IntermediateOutputPath)my-generated-file.xyz" CopyToOutputDirectory="PreserveNewest"/>
    <!-- If you know exactly where that file is going to be, you can hard code the path. -->
    <None Include="some\specific\path\my-generated-file.xyz" CopyToOutputDirectory="PreserveNewest"/>
    
    <!-- If you want to capture "all files of a certain type", you can glob like so. -->
    <None Include="some\specific\path\*.xyz" CopyToOutputDirectory="PreserveNewest"/>
    <None Include="some\specific\path\*.*" CopyToOutputDirectory="PreserveNewest"/>
  </ItemGroup>
</Target>

Adding your generated file to None or Content is sufficient for the build process to see it and copy the files to the output directory. You also want to ensure it gets added at the right time. Ideally, your target runs before BeforeBuild. AssignTargetPaths is another option, as it is the "final stop" before None and Content items (among others) are transformed into new items.

Globbing

It's worth noting that globbing files (including files via wildcards such as *.xyz) will behave according to when the glob took place. A glob outside of a target will only see files visible at the beginning of the build, or during Evaluation phase. A glob inside of a target will see files during a build which, when timed correctly, can capture files generated during the build.