C# Source Generator - warning CS8032: An instance of analyzer cannot be created

Question

I'm trying to build a Source Generator. Right now, just the most basic static method that returns "Hello World".

The generator project builds, but the generated code is not available, the debugger never starts, and the build output shows

CSC : warning CS8032: An instance of analyzer Generator.StaticPropertyEnum.helloWorld cannot be created from ...\bin\Debug\net5.0\Generator.StaticPropertyEnum.dll : Could not load file or assembly 'System.Runtime, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified..

Examples I'm referencing

• Roslyn Team Generator Sample Project
• Roslyn Team Generator Cookbook
• Generator.Equals Project
• How To Debug C# 9 Source Generators

I've tried

• changing the TargetFramework and LanguageVersion of both the generator and test projects
• referencing many version of the analyzer libraries Microsoft.CodeAnalysis.CSharp and Microsoft.CodeAnalysis.Analyzers
• referencing an explicit version of Microsoft.Net.Compilers.Toolset
• Adding an explicit reference to the NetStandard library
• starting from scratch with an analyzer project template
• looking for a generator project template (but didn't find one)

Versions

Visual Studio: version 16.8.3
.NET SDK: 5.0.101

Code

Generator.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net5.0</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.9.0-2.final" PrivateAssets="all" />
    <PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="3.0.0" PrivateAssets="all" />
  </ItemGroup>
</Project>

Test csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net5.0</TargetFramework>
    <IsPackable>false</IsPackable>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.7.1" />
    <PackageReference Include="xunit" Version="2.4.1" />
    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="coverlet.collector" Version="1.3.0">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
  </ItemGroup>
  <ItemGroup>
    <ProjectReference Include="..\Generator.StaticPropertyEnum\Generator.StaticPropertyEnum.csproj"  OutputItemType="Analyzer" ReferenceOutputAssembly="false"/>
  </ItemGroup>
</Project>

Generator

    [Generator]
    public class helloWorld : ISourceGenerator
    {
        public void Execute(GeneratorExecutionContext context)
        {
            context.AddSource("HelloWorld-generated.cs", @"
            using System;
            namespace HelloWorld
            {
                public static class Hello
                {
                    public static string SayHello() {
                        return ""HelloWorld"";
                    }
                }
            }");
        }
        public void Initialize(GeneratorInitializationContext context)
        {
#if DEBUG
            if(!Debugger.IsAttached) Debugger.Launch();
#endif
        }
    }

Solution 1

Source Generators must be .NET Standard 2.0 to run in Visual Studio 2019+ or .NET Standard 1.x to run in Visual Studio 2017+.

Solution 2

as @Yair-Halberstadt mentioned in a different answer, the specific error listed is due to the fact that currently source generator projects need to target netstandard2.0. However if you get the CS8032 error with a different assembly (for example Microsoft.CodeAnalysis, Version=3.0.x ...) your problem is probably caused by a SDK version mismatch. For example on my computer I have SDK 5.0.302 which has version 3.10.0 of Microsoft.CodeAnalysis and Microsoft.CodeAnalysis.CSharp. While the Generator project uses nuget to get these packages, the build of the project referencing the generator resolves these files from the SDK. This is why reverting to 3.8.0 has worked for some commentators, the SDK version they have installed contains 3.8.0 of these references.

Solution 3

I have source generator that targets netstandard2.0 and net5.0 for nullability support.

 <TargetFrameworks>net5.0;netstandard2.0</TargetFrameworks>
 <Nullable>enable</Nullable>

and sample library that targets same frameworks.

It crashes when project is being built within Visual Studio, but builds ok from the terminal.

To solve this, I've changed target framework when referencing it as a generator with SetTagetFramework and now it compiles without any warnings or errors.

  <ItemGroup>
    <ProjectReference Include="..\MyGenerator\MyGenerator.csproj"
                      OutputItemType="Analyzer" ReferenceOutputAssembly="false"
                      SetTargetFramework="TargetFramework=netstandard2.0" />
  </ItemGroup>