通过CompilationAnalysisContext.ReportDiagnostic上报的Roslyn诊断在VS中不显示

问题背景 #

使用Visual Studio 2022的「Analyzer with Code Fix」模板创建Roslyn分析器，单元测试中Rule1（通过SymbolAction上报）和Rule2（通过CompilationAction上报）均能正常生成诊断，但在Visual Studio界面中仅能看到Rule1的诊断。调试确认两个context.ReportDiagnostic调用都已执行，且VS设置中未抑制任何诊断。由于业务需要检查多个符号间的关系，改用SymbolAnalysisContext.ReportDiagnostic重写成本过高。

复现代码 #

[DiagnosticAnalyzer(LanguageNames.CSharp)]
public class DummyAnalyzer : DiagnosticAnalyzer
{
    private static readonly DiagnosticDescriptor Rule1 = new ("D001", "SymbolAction", "SymbolAction", "Test", DiagnosticSeverity.Warning, true);
    private static readonly DiagnosticDescriptor Rule2 = new ("D002", "CompilationAction", "CompilationAction", "Test", DiagnosticSeverity.Warning, true);

    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => [Rule1, Rule2];

    public override void Initialize(AnalysisContext context)
    {
        context.EnableConcurrentExecution();

        context.RegisterSymbolAction(c => c.ReportDiagnostic(Diagnostic.Create(Rule1, c.Symbol.Locations.FirstOrDefault())), SymbolKind.Method);

        context.RegisterCompilationAction(CompilationAction);
    }

    private void CompilationAction(CompilationAnalysisContext context)
    {
        foreach (var syntaxTree in context.Compilation.SyntaxTrees)
        {
            var compilationUnitSyntax = syntaxTree.GetRoot(context.CancellationToken) as CompilationUnitSyntax;
            var typeDeclarationSyntax = compilationUnitSyntax?.Members.OfType<BaseNamespaceDeclarationSyntax>().SelectMany(syntax => syntax.Members).OfType<TypeDeclarationSyntax>().FirstOrDefault();
            if (typeDeclarationSyntax != null)
                context.ReportDiagnostic(Diagnostic.Create(Rule2, typeDeclarationSyntax.GetLocation()));
        }
    }
}

解决方法 #

核心原因 #

Visual Studio的**实时分析（Live Analysis）**默认会跳过全编译级别的分析动作（如CompilationAction），因为这类动作遍历整个编译单元，性能开销较大，仅在全编译（如项目重建）时才会执行。

具体修复步骤 #

1. 配置CompilationAction的执行上下文
   在Initialize方法中，为RegisterCompilationAction添加分析选项，明确指定允许该动作在实时分析中执行：

   context.RegisterCompilationAction(CompilationAction, 
       new CompilationAnalysisOptions(ExecutionContext = AnalysisExecutionContext.LiveAnalysis));
   

2. 优化CompilationAction的性能
   实时分析会频繁触发，必须确保动作执行高效，避免卡顿。可以限制仅处理当前活跃文档的语法树：

   private void CompilationAction(CompilationAnalysisContext context)
   {
       // 获取当前活跃文档路径（仅在VS实时分析中有效）
       context.Options.AnalyzerConfigOptionsProvider.GlobalOptions.TryGetValue(
           "build_metadata.AdditionalFiles.ActiveDocumentPath", 
           out var activeDocumentPath);
   
       foreach (var syntaxTree in context.Compilation.SyntaxTrees)
       {
           // 跳过非活跃文档的语法树，减少不必要的计算
           if (!string.IsNullOrEmpty(activeDocumentPath) && 
               !syntaxTree.FilePath.Equals(activeDocumentPath, StringComparison.OrdinalIgnoreCase))
           {
               continue;
           }
   
           var compilationUnitSyntax = syntaxTree.GetRoot(context.CancellationToken) as CompilationUnitSyntax;
           var typeDeclarationSyntax = compilationUnitSyntax?.Members.OfType<BaseNamespaceDeclarationSyntax>()
               .SelectMany(syntax => syntax.Members)
               .OfType<TypeDeclarationSyntax>()
               .FirstOrDefault();
           
           if (typeDeclarationSyntax != null)
           {
               context.ReportDiagnostic(Diagnostic.Create(Rule2, typeDeclarationSyntax.GetLocation()));
           }
       }
   }
   

3. 验证全编译场景
   如果配置后实时分析仍未显示诊断，可以右键项目选择「重建」触发全编译，确认诊断是否出现，以此排除增量分析的干扰。

内容的提问来源于stack exchange，提问作者Dark Daskin