Adding any files from old NuGet packages projects into .NET Core SDK-based MSBuild projects

Publication date: 2018-05-24

Not so long ago, while working on an open-source project, I had to solve an problem: how to integrate an old C++/CLI NuGet package (built in 2012) that's compatible only with full .NET Framework with the project built using .NET Core SDK. While solving the issue I encountered some interesting historical and engineering facts about MSBuild and NuGet, and finally I've solved the problem.

The package in question includes multiple native DLLs. That means that my project couldn't have any references to these DLLs, but I need these files in my output directory (like bin/Debug) to run the project.

For example, there's a file lib/net20/Cosmo.dll and it should be placed into the same directory MyProject.exe is placed after the build.

This package works correctly with "old" .NET SDK, because for old SDK, MSBuild was copying everything from the lib/net20 directory into the output directory. For new SDK (and actually for old SDK, too) package authors should've used contentFiles, although, obviously, it's unlikely they will fix their C++/CLI package to be compoatible with .NET Core SDK: it's not in fact compatible with .NET Core at all, so why bother?

Fortunately, MSBuild is flexible enough to fix the issue from our side by writing some additional XML. We'll create a package file list manually (note that wildcards are supported) and make MSBuild to copy these files for us.

The following code should be included into the <Project> element in your .csproj:

<PackageReference Include="$(ActivizNetPackage)" Version="$(ActivizNetVersion)"/>
    <Content CopyToOutputDirectory="Always" Include="$(ActivizNetContents)">
    <Content Remove="$(ActivizNetExclude)" />

This sample shows how to get package content path (via the NuGetPackageRoot builtin variable) and how to add package content into your project (optionally excluding some items with <Content Remove="…"/>).

Using this mechanic, you can create a .NET Core SDK project that will use any old NuGet packages relied on this MSBuild+NuGet quirk.