Help: Suppressing Roslyn rules in generated code when TreatWarningAsErrors is true

[nschuessler]

We wrote a rule that flags string.Format when there are 4 or fewer arguments (because string.Concat or the $"" format which is string.Concat underneath are better options).

Unfortunately, System.Text.Json generates serialization code with an error message that violates this rule. With TreatWarningsAsErrors enabled this fails the build.

There are a few scenarios we've tried to suppress it, but it appears to be ignored by .editor.config and the globalsuppressions system (I didn't personally verify this one -- verified by customer of our rules).

The only way to suppress it is on the command line, globally, for the whole project.

Q1: What is the most supported way to do fine tuned configuration of suppressions? I thought .editor.config superseeded .rulesets but maybe that's not the case?

Q2: Should the analyzer itself be looking at settings and not supporting generated code if it sees something in .editor.config (i.e. the following initialization code should have a conditional on the generated code analyis:

       public override void Initialize(AnalysisContext context)
       {
           // This allows parallel analysis of methods and types
           // and requires proper synchronization if needed in the analyzer
           context.EnableConcurrentExecution();
           context.RegisterCompilationStartAction(this.OnStartCompilation);
           context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.Analyze | GeneratedCodeAnalysisFlags.ReportDiagnostics);
       }

Q3: How does // <autogenerated /> and #pragma warning disable fit in with suppression (i.e. if we could inject the latter, the former is already in the generated code and doesn't affect anything).

Q4: We found the following issue on this matter that seems related and resolved in .Net 8, but still seems to repro / doesn't seem to help in the latest bits (Roslyn 4.10).

Adding <CodeAnalysisTreatWarningsAsErrors>true</CodeAnalysisTreatWarningsAsErrors> to the file with TreatWarningsAsErrors as either true or false doesn't seem to have any effect. What should we be doing here?

Project file:

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

  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Contoso.OurAnalyzers" Version="311.21.1022.2">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.4.0" />
  </ItemGroup>

 
</Project>

Editor config entries:

dotnet_diagnostic.CPR105.severity = none
dotnet_diagnostic.CPR138.severity = none
dotnet_diagnostic.CPR126.severity = none

[sharwell]

Why is this analyzer using GeneratedCodeAnalysisFlags.ReportDiagnostics? As a performance analyzer, it seems like it should not be reporting diagnostics in generated code, as there is no way for a user to address those warnings.

[nschuessler]

I was either following an example, or when I was writing tests against the code library it was failing to pass in the generated scenario. There is also I think a analyzer rule for Roslyn that flag it if you don't specify the initialization that may have fiddled with it as a result.

In any case, what is the scenario where generated code should be analyzed?
Should the default be for most analyzers .None then?