Warning NU5118 packaging RCL with static contents and multi-target frameworks netcoreapp3.1;net5.0

[tmm360]

Details about Problem

Trying to package a Razor Class Library that contains static contents, and that multi-targets the frameworks netcoreapp3.1 and net5.0, I receive several NU5118 warnings. I'm using dotnet pack command from stable .NET 5 SDK. Building works without warnings, packaging no.

dotnet.exe --version: 5.0.100
VS version: 16.8.0

Detailed repro steps so we can see the same problem

1. Create a new RCL project with this minimal project file:

<Project Sdk="Microsoft.NET.Sdk.Razor">

  <PropertyGroup>
    <TargetFrameworks>netcoreapp3.1;net5.0</TargetFrameworks>
  </PropertyGroup>

</Project>

2. Add a wwwroot directory with a sample static file inside

3. Try to pack it with dotnet pack, or VS UI.

Logs

1>------ Build started: Project: RazorClassLibrary1, Configuration: Debug Any CPU ------
1>RazorClassLibrary1 -> C:\Users\mirko\Desktop\wow\WebApplication1\RazorClassLibrary1\bin\Debug\net5.0\RazorClassLibrary1.dll
1>RazorClassLibrary1 -> C:\Users\mirko\Desktop\wow\WebApplication1\RazorClassLibrary1\bin\Debug\netcoreapp3.1\RazorClassLibrary1.dll
1>C:\Program Files\dotnet\sdk\5.0.100\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(207,5): warning NU5118: File 'C:\Users\mirko\Desktop\wow\WebApplication1\RazorClassLibrary1\wwwroot\background.png' is not added because the package already contains file 'staticwebassets\background.png'
1>C:\Program Files\dotnet\sdk\5.0.100\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(207,5): warning NU5118: File 'C:\Users\mirko\Desktop\wow\WebApplication1\RazorClassLibrary1\obj\Debug\netcoreapp3.1\staticwebassets\msbuild.RazorClassLibrary1.Microsoft.AspNetCore.StaticWebAssets.props' is not added because the package already contains file 'build\Microsoft.AspNetCore.StaticWebAssets.props'
1>C:\Program Files\dotnet\sdk\5.0.100\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(207,5): warning NU5118: File 'C:\Users\mirko\Desktop\wow\WebApplication1\RazorClassLibrary1\obj\Debug\netcoreapp3.1\staticwebassets\msbuild.build.RazorClassLibrary1.props' is not added because the package already contains file 'build\RazorClassLibrary1.props'
1>C:\Program Files\dotnet\sdk\5.0.100\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(207,5): warning NU5118: File 'C:\Users\mirko\Desktop\wow\WebApplication1\RazorClassLibrary1\obj\Debug\netcoreapp3.1\staticwebassets\msbuild.buildMultiTargeting.RazorClassLibrary1.props' is not added because the package already contains file 'buildMultiTargeting\RazorClassLibrary1.props'
1>C:\Program Files\dotnet\sdk\5.0.100\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(207,5): warning NU5118: File 'C:\Users\mirko\Desktop\wow\WebApplication1\RazorClassLibrary1\obj\Debug\netcoreapp3.1\staticwebassets\msbuild.buildTransitive.RazorClassLibrary1.props' is not added because the package already contains file 'buildTransitive\RazorClassLibrary1.props'
1>Successfully created package 'C:\Users\mirko\Desktop\wow\WebApplication1\RazorClassLibrary1\bin\Debug\RazorClassLibrary1.1.0.0.nupkg'.
1>Done building project "RazorClassLibrary1.csproj".
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

Sample Project

RazorClassLibrary1.zip

[tmm360]

This looks to be fixed

[bigabdoul]

This issue is old, but it still does not unambiguously resolve the root cause. After investigating, I noticed that the issue arose from the lack of the Razor Language Version specification when targeting multiple frameworks. In other words, there should be an explicit and appropriate Razor Language Version property group for each target framework. The above project file should look like:

<Project Sdk="Microsoft.NET.Sdk.Razor">

  <PropertyGroup>
    <TargetFrameworks>netcoreapp3.1;net5.0</TargetFrameworks>
  </PropertyGroup>

  <PropertyGroup Condition="'$(TargetFramework)' == 'netcoreapp3.1'">
    <RazorLangVersion>3.0</RazorLangVersion>
  </PropertyGroup>

  <PropertyGroup Condition="'$(TargetFramework)' == 'net5.0'">
    <RazorLangVersion>5.0</RazorLangVersion>
  </PropertyGroup>
</Project>