如何在Roslyn中获取未解析的符号？

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        // 示例源代码
        string sourceCode = @"
            using System;
            class Example
            {
                void Method()
                {
                    var x = NonExistentMethod();
                }
            }";

        // 创建语法树
        var syntaxTree = CSharpSyntaxTree.ParseText(sourceCode);

        // 创建语义模型
        var compilation = CSharpCompilation.Create("Example", syntaxTrees: new[] { syntaxTree });
        var semanticModel = compilation.GetSemanticModel(syntaxTree);

        // 遍历语法节点
        var root = syntaxTree.GetRoot();
        var unresolvedSymbols = new List<UnresolvedSymbolInfo>();

        foreach (var node in root.DescendantNodes())
        {
            if (node is InvocationExpressionSyntax invocation)
            {
                var symbolInfo = semanticModel.GetSymbolInfo(invocation.Expression);
                if (symbolInfo.Symbol == null && symbolInfo.CandidateSymbols.Length == 0)
                {
                    unresolvedSymbols.Add(new UnresolvedSymbolInfo
                    {
                        Node = invocation,
                        Message = "Unresolved symbol"
                    });
                }
            }
        }

        // 输出未解析的符号信息
        foreach (var unresolvedSymbol in unresolvedSymbols)
        {
            Console.WriteLine($"Unresolved symbol at line {unresolvedSymbol.Node.GetLocation().GetLineSpan().StartLinePosition.Line + 1}: {unresolvedSymbol.Node.ToFullString()}");
        }
    }
}

class UnresolvedSymbolInfo
{
    public SyntaxNode Node { get; set; }
    public string Message { get; set; }
}