Roslyn analyzer missing assembly warning

Some background on this issue is here. When an analyzer depends on another assembly, then both must be listed as analyzers, but there is generally an exception for the core system assemblies. Unfortunately, it does not appear that .Net standard 2.0 has yet been added to the exceptions list; presumably, that will occur at some point in the future. I was able to make code changes to target the analyzer to .Net Standard 1.3 instead, thus avoiding the warning.

This problem will also arise when adding other assemblies (such as Newtonsoft.Json) into your analyzer. One solution to this is simply not to do so; for example, StyleCop eliminated its dependence on Newtonsoft.Json and simply includes the code for LightJson directly in its assembly. Other solutions might be (1) to manually copy the dll you are depending on (taking it from your packages folder if necessary) into the .nupkg file, recognizing that .nupkg is really just a .zip file; or (2) to use a tool like ILMerge to merge the dependency into your DLL. I have not yet experimented with these approaches, so if someone else can produce a step-by-step explanation of how to integrate this into a build for an analyzer, I will mark that as a correct answer.

You can use the approach in the Source Generators Cookbook (Thanks to @mbabramo for the link!).

<ItemGroup>
<PackageReference Include="Analyzer4" Version="1.0.0.1" />
</ItemGroup>

Becomes:

<ItemGroup>
<PackageReference Include="Analyzer4" Version="1.0.0.1" PrivateAssets="all" GeneratePathProperty="true" />
<None Include="$(PkgAnalyzer4)\lib\netstandard2.0\*.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
</ItemGroup>

This should add the package dlls into your analyzer's folder, and it should work.