NuGet: Two packages with targets files lead to incorrectly copied DLLs

Question

I have created two NuGet packages that contain Native Libraries. The first one has two subfolders (amd64 and x86) the second one includes the DLL flat under the build directory. The NativeLibraries of the the first package are supposed to be copied into subfolders of the OutputPath. The only DLL in the second package should be copied flat under the OutputPath. I used the following stackoverflow entry as a guide for creating the package: https://stackoverflow.com/a/30316946/4496150

The first NuGet package folder structure looks like this (amd64 and x86 subfolder under build):

• build
  • amd64
    • DLL1.dll
    • DLL2.dll
  • x86
    • DLL1.dll
    • DLL2.dll
  • packagename.targets

First targets file:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <ItemGroup>
    <NativeLibs Include="$(MSBuildThisFileDirectory)**\*.dll" />
    <None Include="@(NativeLibs)">
      <Link>%(RecursiveDir)%(FileName)%(Extension)</Link>
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
  </ItemGroup>
</Project>

Please notice $(MSBuildThisFileDirectory)** as NativeLibs Include and %(RecursiveDir) as part of Link attribute.

The second NuGet package structure looks like this (no subfolders under build):

• build
  • DLL1.dll
  • packagename.targets

Second targets file:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <ItemGroup>
    <NativeLibs Include="$(MSBuildThisFileDirectory)\*.dll" />
    <None Include="@(NativeLibs)">
      <Link>%(FileName)%(Extension)</Link>
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
  </ItemGroup>
</Project>

Please notice $(MSBuildThisFileDirectory) (without **) as NativeLibs Include and missing %(RecursiveDir) in Link attribute.

If you reference both packages, the DLLs from the first package are additionally copied flat into the output folder, which is not desired. I suspect this is because the second include step also reads the DLLs from the first package, but then does not use %(RecursiveDir).

A workaround is to also include in the second package both. and NativeLibs Include="$(MSBuildThisFileDirectory)***.dll" /> exactly as in the first package.

However, I would prefer to understand why the second package ensures that the DLLs from the first are copied flat.

If I read https://learn.microsoft.com/de-de/visualstudio/msbuild/msbuild-reserved-and-well-known-properties?view=vs-2019 correctly, $(MSBuildThisFileDirectory) points to the folder in my NuGet cache where the targets file of the NuGet package is located. So actually everything would be correct. But still (probably) wrong DLLs are copied.

Edit

I added the following snippet in both targets files to get some output:

<Target Name="OutputPackage1NativeLibs" BeforeTargets="Build">
    <Message Text="Package1 %(NativeLibs.Identity)" Importance="high"/>
</Target>

For the seconds targets file I changed the target name to OutputPackage2NativeLibs and started the text Output with Packag2.

When I clean my NuGet Package Cache and rebuild the solution everything is fine. But after the third or forth rebuild operation the DLLs of the first package are copied flat under the Output path and I get the following output:

Package1 C:\Users\USERNAME\.nuget\packages\PACKAGENAME1\1.2.3.4\build\amd64\DLL1.dll
Package1 C:\Users\USERNAME\.nuget\packages\PACKAGENAME1\1.2.3.4\build\amd64\DLL2.dll
Package1 C:\Users\USERNAME\.nuget\packages\PACKAGENAME1\1.2.3.4\build\x86\DLL1.dll
Package1 C:\Users\USERNAME\.nuget\packages\PACKAGENAME1\1.2.3.4\build\x86\DLL2.dll
Package1 C:\Users\USERNAME\.nuget\packages\PACKAGENAME2\1.0.0.0\build\DLL1.dll

Package2 C:\Users\USERNAME\.nuget\packages\PACKAGENAME1\1.2.3.4\build\amd64\DLL1.dll
Package2 C:\Users\USERNAME\.nuget\packages\PACKAGENAME1\1.2.3.4\build\amd64\DLL2.dll
Package2 C:\Users\USERNAME\.nuget\packages\PACKAGENAME1\1.2.3.4\build\x86\DLL1.dll
Package2 C:\Users\USERNAME\.nuget\packages\PACKAGENAME1\1.2.3.4\build\x86\DLL2.dll
Package2 C:\Users\USERNAME\.nuget\packages\PACKAGENAME2\1.0.0.0\build\DLL1.dll

So NativeLibs are added from the other NuGet package apparently after the third or fourth rebuild.

Answer 1

I think you are using Packages.config nuget package format with non-sdk net framework projects. If so, that could be explained.

For packages.config nuget management format, it imports the target files directly under csproj file. In my side, I created two nuget packages called flat 1.0.0 and faltt 1.0.0 nuget packages.

You can check my csproj file:

If so, the first import targets file flat.targets file is the same as your first nuget package's targets file:

It includes the x86 and amd64 folder files into output folder\x86 and output folder\amd64 folder, that is right as we excepted.

However, under pakckages.config, since the two targets file are in the same csproj file, they can access each other(they have the same life cycle in the same CSProj), when msbuild reads faltt.targets file after flat.targets file, also you did not change NativeLibs item for the second targets file, itself has the file:

C:\Users\xxx\source\repos\flat\packages\flat.1.0.0\build\amd64\Dll1.dll
C:\Users\xxx\source\repos\flat\packages\flat.1.0.0\build\amd64\Dll2.dll
C:\Users\xxx\source\repos\flat\packages\flat.1.0.0\build\x86\Dll1.dll
C:\Users\xxx\source\repos\flat\packages\flat.1.0.0\build\x86\Dll1.dll

When reads the flatt.targets file, it also includes C:\Users\xxx\source\repos\flat\packages\flatt.1.0.0\build\x86\Dll1.dll,

So it has five files under NativeLibs item.

And then it executes <Link>%(FileName)%(Extension)</Link>, the first nuget package's dlls will be executed under the second nuget packages's node, output to the output root folder.

Because of the special nature of Packages.config import targets files, they are interlaced.

You should note that

Under PackageReference nuget management format, the import targets files are stored under obj\xxx.csproj.nuget.g.targets file, like this:

 <ImportGroup Condition=" '$(ExcludeRestorePackageImports)' != 'true' ">
    <Import Project="$(NuGetPackageRoot)flatt\1.0.0\build\flatt.targets" Condition="Exists('$(NuGetPackageRoot)flatt\1.0.0\build\flatt.targets')" />
    <Import Project="$(NuGetPackageRoot)flat\1.0.0\build\flat.targets" Condition="Exists('$(NuGetPackageRoot)flat\1.0.0\build\flat.targets')" />
  </ImportGroup>

Since the content is not in csproj file and the particularity of the file xxx.csproj.nuget.g.targets, it will read the targets files in each nuget package separately. Each file is a separate life cycle, so it does not Will affect each other. This is also one of the advantages of the latest PackagesReference nuget management format.

Sorry for not telling you at the beginning that I was using packagesReference and I didn't notice packages.config.

So if you want to get the right behavior to separate them, try the two approaches:

1) do not change the two nuget packages, right-click on the packages.config file of the main project which installs the two nuget packages-->click Migrate packages.config to PackageReference option

After that, click Rebuild option to get that.

2) modify the nuget packages--> change the NativeLibs item's name to another for the second nuget package targets file:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <ItemGroup>
    <NativeLibs1 Include="$(MSBuildThisFileDirectory)*.dll" />
    <None Include="@(NativeLibs1)">
      <Link>%(FileName)%(Extension)</Link>
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
  </ItemGroup>
</Project>

When re-pack your project, uninstall them first, delete all cache files under C:\Users\xxx\.nuget\packages. And then re-install the packages again.