测试源生成器答案

【问题标题】：Testing source generator测试源生成器
【发布时间】：2021-11-06 06:00:33
【问题描述】：

我正在尝试测试源生成器。生成器：

[Generator]
public class CustomGenerator : ISourceGenerator
{
    public void Initialize(GeneratorInitializationContext context) { }

    public void Execute(GeneratorExecutionContext context)
    {
        //...
    }
}

测试代码：

              Compilation inputCompilation = CreateCompilation(@"
namespace MyCode
{
    public class Program
    {
        public static void Main(string[] args)
        {
        }
    } 
}
");   
            var generator = new CustomGenerator();
             
            var driver = CSharpGeneratorDriver.Create(generator);
             
            driver.RunGeneratorsAndUpdateCompilation(inputCompilation, out var outputCompilation, out var diagnostics);

            static Compilation CreateCompilation(string source)
                => CSharpCompilation.Create("compilation",
                    new[] { CSharpSyntaxTree.ParseText(source) },
                    new[] { MetadataReference.CreateFromFile(typeof(Binder).GetTypeInfo().Assembly.Location) },
                    new CSharpCompilationOptions(OutputKind.ConsoleApplication));

问题是 context.SyntaxReceiver 总是为空，如何解决？

【问题讨论】：

您需要首先在您的Initialize 方法中注册一个语法接收器，方法是调用context.RegisterForSyntaxNotifications。见the cookbook。

标签： c# roslyn roslyn-code-analysis

【解决方案1】：

让我们检查GeneratorExecutionContext.SyntaxReceiver属性的定义：

namespace Microsoft.CodeAnalysis
{
    public readonly struct GeneratorExecutionContext
    {
        // Summary:
        //     If the generator registered an Microsoft.CodeAnalysis.ISyntaxReceiver during
        //     initialization, this will be the instance created for this generation pass.
        public ISyntaxReceiver? SyntaxReceiver { get; }
    }
}

我们看到GeneratorExecutionContext.SyntaxReceiver 属性被声明为可为空，这意味着在某些情况下它确实应该为空。文档注释显示我们首先必须在ISourceGenerator.Initialize 中注册我们的ISyntaxReceiver。

正如canton7所指出的，我们首先需要通过GeneratorInitializationContext.RegisterForSyntaxNotifications方法注册它：

[Generator]
public class CustomGenerator : ISourceGenerator
{
    public void Initialize(GeneratorInitializationContext context)
    {
        context.RegisterForSyntaxNotifications(static () => new CustomReceiver());
    }

    public void Execute(GeneratorExecutionContext context)
    {
        Debug.Assert(context.SyntaxReceiver is not null, $"No {nameof(ISyntaxReceiver)} registerd via {nameof(GeneratorInitializationContext.RegisterForSyntaxNotifications)}.");

        if (context.SyntaxReceiver is not CustomReceiver receiver)
        {
            return;
        }

        Debug.Assert(receiver is not null);

        //...
    }
}

internal sealed class CustomReceiver : ISyntaxReceiver
{
    public void OnVisitSyntaxNode(SyntaxNode syntaxNode)
    {
    }
}

请记住避免在 ISyntaxReceiver 中进行昂贵的操作，因为它不支持取消不像 Generator 本身。

【讨论】：