c# - 确定是否使用 Roslyn 读取私有(private)字段

Question

我已经搜索了一整天并阅读了很多帖子，但我无法对此得出结论。我正在尝试创建一个 Roslyn 分析器，以便在私有(private)字段未读时报告诊断。注册语法操作并确定其私有(private)是否真的很容易。但现在我一直在尝试找出该字段是否在类中被读取。

假设我们有以下示例代码:

public class C {
    private int foo; //private field is declared but never read. Should report diagnostic here
    
    public void DoNothing() {
        //irrelevant
    }
}

有几个例子说明我希望在哪里标记此标记(是否初始化、是否注入(inject)、单行上的多个声明等)，但我认为也许它们对于说明问题不是必需的。

到目前为止我所拥有的是:

public override void Initialize(AnalysisContext context) {
    context.EnableConcurrentExecution();
    context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);

    context.RegisterSyntaxNodeAction(AnalyzeField, SyntaxKind.FieldDeclaration);
}

private void AnalyzeField(SyntaxNodeAnalysisContext context) {
    if (!(context.Node is FieldDeclarationSyntax fieldDeclarationSyntax)) {
        return;
    }

    foreach (var variableDeclaration in fieldDeclarationSyntax.Declaration.Variables) {
        if (context.SemanticModel.GetDeclaredSymbol(variableDeclaration) is IFieldSymbol variableDeclarationSymbol &&
            IsFieldPrivate(variableDeclarationSymbol) &&
            !IsFieldRead(context, variableDeclarationSymbol)) {
            
            //report diagnostic here
        }
    }
}

private bool IsFieldPrivate(IFieldSymbol fieldSymbol) {
    return fieldSymbol.DeclaredAccessibility == Accessibility.Private || // the field itself is explicitly private
           fieldSymbol.ContainingType?.DeclaredAccessibility == Accessibility.Private; //the field is not private, but is contained within a private class
}

private bool IsFieldRead(SyntaxNodeAnalysisContext context, IFieldSymbol fieldSymbol) {
    //context.Node.Parent will be the class declaration here since we're analyzing a field declaration
    //but let's be safe about that just in case and make sure we traverse up until we find the class declaration
    var classDeclarationSyntax = context.Node.Parent;
    while (!(classDeclarationSyntax is ClassDeclarationSyntax)) {
        classDeclarationSyntax = classDeclarationSyntax.Parent;
    }
    var methodsInClassContainingPrivateField = classDeclarationSyntax.DescendantNodes().OfType<MethodDeclarationSyntax>().ToImmutableArray();
    foreach (var method in methodsInClassContainingPrivateField) {
        var dataFlowAnalysis = context.SemanticModel.AnalyzeDataFlow(method); //does not work because this is not a StatementSyntax or ExpressionSyntax
        if (dataFlowAnalysis.ReadInside.Contains(fieldSymbol) || dataFlowAnalysis.ReadOutside.Contains(fieldSymbol)) {
            return true;
        }
    }

    return false;
}

我只是不太清楚如何让 IsFieldRead() 方法发挥作用。这确实感觉像是一件应该很容易做到的事情，但我就是无法完全理解它。我认为获取方法并分析我的领域的方法，看看它是否被读取将是一个不错的主意，但这并不包括该领域是否被另一个私有(private)领域读取，而且我无论如何也无法让它工作。 :)

Answer 1

感谢this other SO answer，我成功地解决了这个问题。由真正在微软从事 Roslyn 工作的人撰写。现在这是我的 IsFieldRead() 方法。关键显然在于 Microsoft.CodeAnalysis.Operations 命名空间。

private bool IsFieldRead(SyntaxNodeAnalysisContext context, IFieldSymbol fieldSymbol) {
    var classDeclarationSyntax = context.Node.Parent;
    while (!(classDeclarationSyntax is ClassDeclarationSyntax)) {
        classDeclarationSyntax = classDeclarationSyntax.Parent;
        if (classDeclarationSyntax == null) {
            throw new InvalidOperationException("You have somehow traversed up and out of the syntax tree when determining if a private member field is being read.");
        }
    }

    //get all methods in the class
    var methodsInClass = classDeclarationSyntax.DescendantNodes().OfType<MethodDeclarationSyntax>().ToImmutableArray();
    foreach (var method in methodsInClass) {
        //get all member references in those methods
        if (context.SemanticModel.GetOperation(method).Descendants().OfType<IMemberReferenceOperation>().ToImmutableArray().Any(x => x.Member.Equals(fieldSymbol))) {
            return true;
        }
    }

    return false;
}

请注意，这仅涵盖方法内的用法。还有其他几个地方，例如其他字段、属性和构造函数，也需要检查。