ReferencePathWithRefAssemblies missing for CoreCompile during DesignTime builds in Ionide.ProjInfo

[TheAngryByrd]

👋 Hey there!

I've been running down the issue ionide/proj-info#171 with regard to getting Ionide.ProjInfo working on dotnet 7. After doing some updates, I was able to get it to load projects but when trying to typecheck files, Fsharp.Compiler.Service would give the error:

Assembly: The system type 'System.Array'  was required but no referenced system DLL

Since System.Array is in System.Runtime.dll I started looking at the difference in dlls that ProjInfo finds
With a working version it finds in in the References C:\\Program Files\\dotnet\\packs\\Microsoft.NETCore.App.Ref\\6.0.9\\ref\\net6.0\\System.Runtime.dll With a nonworking version, it doesn't find find it in the references, and just looks it up via C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.8\Facades\System.Runtime.dll.

So after doing some binlog investigation I noticed that the FSCTask for the 7 branch was not outputting any reference files.

Working .net 6 version:

Not working dotnet 7 version:

There was a change recently #13567 that changed the Inputs of the CoreCompile step to use ReferencePathWithRefAssemblies instead of the previous ReferencePath. Looking for where that pops up, I found over in the Roslyn targets, a shim for this:

  <Target Name="ShimReferencePathsWhenCommonTargetsDoesNotUnderstandReferenceAssemblies"
          BeforeTargets="CoreCompile"
          Condition="'@(ReferencePathWithRefAssemblies)' == ''">
    <!-- 
      FindReferenceAssembliesForReferences target in Common targets populate this item 
      since dev15.3. The compiler targets may be used (via NuGet package) on earlier MSBuilds. 
      If the ReferencePathWithRefAssemblies item is not populated, just use ReferencePaths 
      (implementation assemblies) as they are.
      
      Since XAML inner build runs CoreCompile directly (instead of Compile target),
      it also doesn't invoke FindReferenceAssembliesForReferences listed in CompileDependsOn.
      In that case we also populate ReferencePathWithRefAssemblies with implementation assemblies.
    -->
    <ItemGroup>
      <ReferencePathWithRefAssemblies Include="@(ReferencePath)" />
    </ItemGroup>
  </Target>

I added this to my local Microsoft.FSharp.targets file and it seems to resolve the issue.

Screenshot of it working on dotnet 7

---

I discussed this with @vzarytovskii @baronfel on FSSF Slack. I can send a PR for this shim or if anyone knows of another way to get ReferencePathWithRefAssemblies set during DesignTime related build.

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[TheAngryByrd]

Well I just ended up following a thread dotnet/roslyn#19146 (comment) that talks about how to make sure that ReferencePathWithRefAssemblies is not empty. Adding FindReferenceAssembliesForReferences to ProjInfo seems to work.

Given that I don't think there's actually an issue here now. Feel free to close this.

[TheAngryByrd]

@baronfel mentioned in the issue in ProjInfo there's probably some work around aligning with Roslyn behavior as they might not be having this issue, so I'll let y'all decide if you want to use this issue or open a new one.

[vzarytovskii]

@KevinRansom shall we include it to our target files, so people don't need to do workarounds?

[KevinRansom]

@vzarytovskii yes