C# 源代码生成器：通过命令行属性或预处理器定义常量有条件地生成代码

Question

I am writing a source generator using the incremental generator approach.

I want to allow the developers to be able to conditionally generate some extra code (eg extra comments, debug printouts, pedantic validations in the generated code, etc.) and I would like this to be controlled by either:

• DefineConstants by adding the following to the .csproj file of the project using my source generator:

<PropertyGroup>
  <DefineConstants>$(DefineConstants);MY_PROJECT_EXTRA</DefineConstants>
</PropertyGroup>

• or via the -p: option on the do.net build command line:

dotnet build ProjectUsingMySourceGeneratorCode.csproj -p:MyProjectExtra=true

I checked the following types I have access to: IncrementalGeneratorInitializationContext , SourceProductionContext , Compilation but could not find anything.

As workaround I could add a custom attribute that developers can use to decorate the syntax elements they want to control, but this might require developers to add the attribute many classes/methods manually.

Is there a way I can access either (or both) DefineConstants or command line -p: properties (or any other compile-time settings) inside the IncrementalGenerator workflow?

Answer 1

Thanks to comment from @caton7 I was able to find a way an initial solution using .editorconfig . I think incremental generators might work slightly different than original source generators so I ended up doing something similar to https://github.com/do.net/roslyn/blob/main/docs/features/source-generators.cookbook.md#access-analyzer-config-properties .

My solution

.editorconfig

myvalue = foo

SourceGenerator.cs

public class SourceGenerator : IIncrementalGenerator {
   public void Initialize(IncrementalGeneratorInitializationContext context)
   {
       // Step 1. Identify the classes.
       var classDeclarations = context.SyntaxProvider.CreateSyntaxProvider(
                static (node, ct) => true /* Update with your code */,
                static (context, ct) => context.Node as ClassDeclarationSyntax /* Update with your code*/)
            .Where(CommonExtensions.IsNotNull);

       // Step 2. Combine analyser, compilation and class declaration
       var analizerConfigOptionsCompilationAndClasses = context
            .AnalyzerConfigOptionsProvider
            .Combine(context
                .CompilationProvider
                .Combine(classDeclarations.Collect()));

       // Step 3. Register the source output to generate the code.
       context.RegisterSourceOutput(
            analizerConfigOptionsCompilationAndClasses,
            static (context, settings) => Execute(context, settings.Left, settings.Right.Left, settings.Right.Right));
    }

   private static Execute(SourceProductionContext context, AnalyzerConfigOptionsProvider analyzerConfigOptionsProvider, Compilation compilation, ImmutableArray<ClassDeclarationSyntax?> classDeclarationSyntaxes))
   {
      // NOTE: Unsure why by analyzerConfigOptionsProvider.TryGetValue("myvalue", out var x) would never return the values I would be expecting.

      foreach (var classDeclarationSyntax in classDeclarationSyntaxes)
      {
         if (classDeclarationSyntax is null)
         {
            continue;
         }

         var options = analyzerConfigOptionsProvider.GetOptions(classDeclarationSyntax.SyntaxTree);
         options.TryGetValue("myvalue", out string? myvalue);
         /* myvalue should now be equal to the string foo as defined in .editorconfig */
      }
   }
}