Conditional PackageReference version splitting analyzer presence fails

If a project references two different versions of the same package in two different TargetFrameworks, and the package has added or removed a Roslyn analyzer, the analyzer will be added from both versions of the package, even the one where it’s not present.

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

  <PropertyGroup>
    <TargetFrameworks>net6.0;net472</TargetFrameworks>
    <RootNamespace>two_systemtextjson</RootNamespace>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="System.Text.Json" Version="4.7.0" Condition=" '$(TargetFramework)' == 'net472' " />
    <PackageReference Include="System.Text.Json" Version="6.0.0-preview.4.21253.7" Condition=" '$(TargetFramework)' == 'net6.0' " />
  </ItemGroup>

</Project>

two-systemtextjson on master .NET v6.0.100-preview.5.21302.13 🎯 net6.0;net472 
❯ dotnet build  
Microsoft (R) Build Engine version 17.0.0-preview-21302-02+018bed83d for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  Restored S:\work\two-systemtextjson\two-systemtextjson.csproj (in 135 ms).
  You are using a preview version of .NET. See: https://aka.ms/dotnet-core-preview
  You are using a preview version of .NET. See: https://aka.ms/dotnet-core-preview
CSC : error CS0006: Metadata file 'C:\Users\raines\.nuget\packages\system.text.json\4.7.0\analyzers\dotnet\cs\System.Text.Json.SourceGeneration.dll' could not be found [S:\work\two-systemtextjson\two-systemtextjson.csproj]
  two-systemtextjson -> S:\work\two-systemtextjson\bin\Debug\net6.0\two-systemtextjson.dll

Build FAILED.

CSC : error CS0006: Metadata file 'C:\Users\raines\.nuget\packages\system.text.json\4.7.0\analyzers\dotnet\cs\System.Text.Json.SourceGeneration.dll' could not be found [S:\work\two-systemtextjson\two-systemtextjson.csproj]
    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:01.20

Because 4.7.0 of that package didn’t have an analyzer/source generator, the file isn’t found in that package version. The reference is only there because it was found in the other version.

[Eilon]

We just ran into this with the newly-introduced analyzer in Microsoft.Extensions.Logging.Abstractions 6.0.0-preview.5.21301.5. We found a fairly easy workaround for this, as long as you don’t actually need the analyzer in the project:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFrameworks>netstandard2.1;net6.0-android</TargetFrameworks>
  </PropertyGroup>
  <ItemGroup Condition="'$(TargetFramework.Contains(net6.0))' == 'true'">
    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="6.0.0-preview.5.21301.5" />
  </ItemGroup>
  <ItemGroup Condition="'$(TargetFramework.Contains(net6.0))' != 'true'">
    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="5.0.0" />
  </ItemGroup>

  <!-- Workaround for this bug (replace the analyzer name with the one you need to exclude (filename only, no extension) -->
  <Target Name="RemoveLoggingAnalyzer" BeforeTargets="CoreCompile">
    <ItemGroup>
      <Analyzer Remove="@(Analyzer)" Condition="%(FileName) == 'Microsoft.Extensions.Logging.Generators'" />
    </ItemGroup>
  </Target>
</Project>

[dsplaisted]

I went ahead and sent a PR to fix this: #18877

Thanks to @ericst for identifying where and what the fix was.

I still would really like to see NuGet fix this class of issue by treating analyzers as a proper asset type, though I recognize that’s a lot more complicated.