确定两个SyntaxTokens是否相同

Question

以下面的代码为例:

public class Thing
{
    public int Item { get; }

    public Thing(int item)
    {
        Item = Item; // note incorrect assignment: rhs should be item, the passed-in arg, hence analyzer should warn
    }

    public Thing(Thing other)
    {
      Item = other.Item; // correct assignment, should NOT trigger analyzer
    }
}

我正在编写一个Roslyn分析器来检测和报告这些可能错误的自我分配的情况,以下相关部分:

public override void Initialize(AnalysisContext context)
{
    context.RegisterSyntaxNodeAction(MistakenSelfAssignment, SyntaxKind.SimpleAssignmentExpression);
}

private static void MistakenSelfAssignment(SyntaxNodeAnalysisContext context)
{
    var assignment = context.Node as AssignmentExpressionSyntax;
    if (assignment == null)
    {
        return;
    }

    var leftToken = GetIdentifierToken(assignment.Left);
    var rightToken = GetIdentifierToken(assignment.Right);

    if (leftToken != null && leftToken.IsEquivalentTo(rightToken)) // this never works
    {
        var diagnostic = Diagnostic.Create(Rule, assignment.GetLocation());
        context.ReportDiagnostic(diagnostic);
    }
}

private static SyntaxToken GetIdentifierToken(ExpressionSyntax syntax)
{
    var identifierName = syntax as IdentifierNameSyntax;
    if (identifierName != null)
    {
        return identifierName.Identifier;
    }

    var identifierAccess = syntax as MemberAccessExpressionSyntax;
    if (identifierAccess != null)
    {
        return identifierAccess.Name.Identifier;
    }

    return default(SyntaxToken);
}

但我无法弄清楚如何确定赋值的LHS和RHS是否是相同的标记 - SyntaxToken.IsEquivalentTo似乎是我想要的方法,但它总是返回false,就像SyntaxToken.Equals和==.

确定令牌是否指向自身的正确方法是什么？

Answer 1

我不认为你能在这个SyntaxToken层面上做到这一点。起初，我认为语义模型会在这里帮助你，但在这两种情况下，符号指的是同一事物，所以你不能用它来区分。

但是，您可以做的只是调查SimpleAssignmentExpression，检查两个操作数是否都是标识符，并通过 Marcus 提到的相同方法检查它们的等价性SyntaxFactory.AreEquivalent()。我得到了这个（请参阅此要点以获取完整的 LINQPad 查询）：

假设您编写了这个方法：

private static bool IsAssignmentBad(AssignmentExpressionSyntax assignmentNode)
{
    if (!assignmentNode.IsKind(SyntaxKind.SimpleAssignmentExpression))
    {
        return false;
    }

    var lhs = assignmentNode.Left;
    if (!lhs.IsKind(SyntaxKind.IdentifierName))
    {
        return false;
    }

    var rhs = assignmentNode.Right;
    if (!rhs.IsKind(SyntaxKind.IdentifierName))
    {
        return false;
    }

    return SyntaxFactory.AreEquivalent(lhs, rhs);
}

然后用这个运行它会得到你想要的，我认为：

var tree = CSharpSyntaxTree.ParseText(
@"public class Thing
{
    public int Item { get; }

    public Thing(int item)
    {
        Item = Item; // note incorrect assignment: rhs should be item, the passed-in arg, hence analyzer should warn
    }

    public Thing(Thing other)
    {
        Item = other.Item; // correct assignment, should NOT trigger analyzer
    }
}");

var root = tree.GetRoot();

var incorrectAssignment = root.DescendantNodes().OfType<AssignmentExpressionSyntax>().First();
var correctAssignment = root.DescendantNodes().OfType<AssignmentExpressionSyntax>().Last();

var b1 = IsAssignmentBad(correctAssignment); // doesn't consider the assignment bad
var b2 = IsAssignmentBad(incorrectAssignment); // this one does