Roslyn:检测是否已使用`using`声明了局部变量

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;

string code = @"
using System;
using System.IO;

namespace MyNamespace
{
    class MyClass
    {
        public void MyMethod()
        {
            using (var stream = new FileStream(""file.txt"", FileMode.Open))
            {
                // Code block
            }
        }
    }
}";
SyntaxTree tree = CSharpSyntaxTree.ParseText(code);

var root = (CompilationUnitSyntax)tree.GetRoot();

var usingDeclarations = root.DescendantNodes().OfType<UsingStatementSyntax>();

foreach (var usingDeclaration in usingDeclarations)
{
    var declaredVariables = usingDeclaration.Declaration.Variables;
    foreach (var variable in declaredVariables)
    {
        Console.WriteLine($"局部变量名：{variable.Identifier.Value}");
    }
}