Packaging does not handle a refonly build correctly

Use case: I am trying to generate a reference-assembly-only package for some of our runtime packages. This to allow giving a prospective customer code that compiles, but cannot run.

I’m trying to trigger this using ProduceOnlyReferenceAssembly=true. When this is set, I

• avoid setting GenerateDocumentationFile to true (it would leak information about internals)
• avoid setting ProduceReferenceAssembly to true (refout conflicts with refonly)
• add a .ReferenceAssemblies suffix to PackageId
• set BuildOutputTargetFolder to ref (because the docs say reference assemblies should go there instead of lib)
• set IncludeSymbols to false

The build works fine with that, producing just the reference assembly in the output folder.

However, the pack task complains:

error NU5026: The file '$(OutputPath)\$(Configuration)\$(TargetFramework)\$(TargetName).pdb' to be packed was not found on disk.

I am not asking for a symbols package, not have I otherwise asked for PDB files to be built or packed; the compiler does not seem to produce one at all when refonly is used.

Using the binlog file, I see that the Pack task seems to get the .pdb file names from a _TargetPathsToSymbols item group. Note that while the error refers to the file under OutputPath, the TargetPathsToSymbols being passed actually has them under IntermediateOutputPath (and OutputPath is not being passed).

I suppose there are two separate issues, that combine to form this error:

• the _TargetPathsToSymbols item group is populated with PDB files that are not actually produced by the build
  • this in turn is because _WalkEachTargetPerFramework calls _GetDebugSymbolsWithTfm for each target framework when IncludeBuildOutput is true
    • in and of itself, that seems fine
    • it in turn depends on a DebugSymbolsProjectOutputGroupOutput item group, set by DebugSymbolsProjectOutputGroup
• the Pack task requires the file names passed to its TargetPathsToSymbols parameter to exist even with IncludeSymbols set to false

I can work around the error using

    <Target Name="ThereAreNoPDBFilesAfterARefOnlyBuild"
          AfterTargets="DebugSymbolsProjectOutputGroup"
          Condition=" '$(ProduceOnlyReferenceAssembly)' == 'true' ">
    <ItemGroup>
      <DebugSymbolsProjectOutputGroupOutput Remove="$(IntermediateOutputPath)$(TargetName).pdb" />
    </ItemGroup>
  </Target>

but that is hardly a clean solution, and it then complains about missing reference assemblies:

C:\Program Files\dotnet\sdk\5.0.300\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(221,5): warning NU5131: References were found in the nuspec, but some reference assemblies were not found in both the nuspec and ref folder. Add the following reference assemblies:
C:\Program Files\dotnet\sdk\5.0.300\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(221,5): warning NU5131: - Add $(TargetFileName) to the net472 reference group in the nuspec
C:\Program Files\dotnet\sdk\5.0.300\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(221,5): warning NU5131: - Add $(TargetFileName) to the netcoreapp3.1 reference group in the nuspec
C:\Program Files\dotnet\sdk\5.0.300\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(221,5): warning NU5131:  

The generated .nuspec has

<?xml version="1.0" encoding="utf-8"?>
<package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
  <metadata>
    ...
    <dependencies>
      <group targetFramework=".NETFramework4.7.2" />
      <group targetFramework=".NETCoreApp3.1" />
    </dependencies>
  </metadata>
  <files>
    <file src="$(OutputPath)\Debug\net472\$(TargetFileName)" target="ref\net472\$(TargetFileName)" />
    <file src="$(OutputPath)\Debug\netcoreapp3.1\$(TargetFileName)" target="ref\netcoreapp3.1\$(TargetFileName)" />
  </files>
</package>

Looking at the NU5131 docs, it seems mostly concerned with packages containing both ref and lib assemblies. The suggestion seems to be that something like

<references>
    <group targetFramework="net472">
        <reference file="$(TargetFileName)" />
    </group>
    <group targetFramework="netcoreapp3.1">
        <reference file="$(TargetFileName)" />
    </group>
</references>

is needed, but I can’t immediately find any documentation on how to have the NuGet targets generate that.

[Zastai]

It’s possible that dotnet/msbuild#6510 will resolve things enough, and I do have a workaround for now.

And the remaining element (NU5131) is more a NuGet issue than an SDK one (but I don’t suppose issues can be transferred from the dotnet org to the NuGet one?) - and even that’s avoidable via NoWarn (as much as I dislike having to do that).

I’ll leave it open for a bit, but I would say it’s not currently all that urgent.

[sfoslund]

@Zastai it looks like you found a workaround, is there still an outstanding issue here?