Prevent duplicating files in NuGet content and contentFiles folders

My NuGet package needs to deliver some rather large files to build output directory.

In an old NuGet model, such files have to be stored in content folder of the .nupkg. While in a new model introduced in NuGet 3.3, such files have to be stored in contentFiles folder.

To maintain a compatibility with older versions of NuGet and mainly with Package.config package management format, I need to duplicate the files into both folders. That unfortunately almost doubles a size of the package.

Is there a way to prevent that? Can I somehow link contentFiles to content folder?

Solution

If you only want to output the file to the build output (content only copies the file to the output directory but does cause it to be set as copy to output directory item), you can use a completely different approach by creating an msbuild file that will be included in the project.

You can do this by putting both the file - say test.jpg into the tools folder (you could also use build) and add a Your.Package.Id.targets file to the build folder (the name being the package id of your package with .targets as extension) with the following content:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <ItemGroup>
    <Content Include="$(MSBuildThisFileDirectory)..\tools\test.jpg">
      <Link>test.jpg</Link>
      <Visible>false</Visible>
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
    </Content>
  </ItemGroup>
</Project>

This target will be automatically imported into the project files regardless of which "style" of NuGet reference is used (packages.config, PackageReference) and should be backwards compatible to older versions of VS as long as they support NuGet and ToolsVersion 4.0.

The Link metadata denotes where in the output / publish directories the file will end up. You could set it to e.g. defaultContent\images\foo.jpg to create a nested structure and rename the file. (you could even use MSBulid variables to use some of the referencing project's configuration). The Visible metadata prevents the solution explorer from showing the full relative path to the file, which could end up in lots of nested .. nodes. The CopyToPublishDirectory applies to .NET Core / ASP.NET Core apps or SDK-based projects using the Publish target for publishing.

Note that you can set the Inclue-path to anything depending on where in your package the file is. You can also use wildcards (but then set Link to %(Filename)%(Extension))