可靠地将类型符号（ITypeSymbol）与Roslyn进行比较

我试图在以下情况下可靠地比较 ITypeSymbol 最简单和最直接的两种情况（我在一个更大的项目中遇到了这些问题，并试图尽可能地简化它）：

我有这个SyntaxTree的CSharpCompilation：

namespace MyAssembly
  {
    public class Foo
    {
      public Foo(Foo x)
      {
      }
    }
  }

我们正在使用 CSharpSyntaxRewriter 穿过树，更改类并更新 Compilation . 在第一次运行中，我们记住了第一个构造函数参数的 ITypeSymbol （在这种情况下，这是类本身的类型） . 更新编译后，我们再次调用相同的重写器，并再次从构造函数参数中获取ITypeSymbol . 之后，我比较了两个我希望代表相同类型 MyAssembly.Foo 的ITypeSymbol .

我的第一个比较方法是调用 ITypeSymbol.Equals() 方法，但它返回 false . 它基本上返回 false 因为我们改变了编译并在此期间得到了一个新的 SemanticModel . 如果我们不这样做，Equals（）方法实际上返回true .

比较 DeclaringSyntaxReferences （如此处所述How to compare type symbols (ITypeSymbol) from different projects in Roslyn?）返回false，因为我们在此期间更改了类 Foo 本身 . 如果构造函数参数的类型为 Bar ，那么行为将是相同的，我们重写了 Bar . 要验证这一点，只需取消注释该行

//RewriteBar(rewriter, compilation, resultTree);

并在代码示例中用 Bar 替换构造函数参数类型 .

Conclusion: ITypeSymbol.Equals() 不适用于新的编译和语义模型，并且比较 DeclaringSyntaxReferences 不适用于我们在此期间更改的类型 . （我还测试了一种外部程序集的行为 - 在这种情况下，ITypeSymbol.Equals（）为我工作 . ）

So my questions are:

• 在描述的情况下比较类型的预期方法是什么？

• 是否有单一的全能解决方案或者我是否需要混合/组合不同的方法来确定类型相等（也可能考虑完全限定名称的字符串表示）？

这是完整的测试程序，使用该程序可以重现该问题 . 只需复制，包含Roslyn引用并执行：

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

namespace Demo.TypeSymbol
{
  class Program
  {
    static void Main(string[] args)
    {    
      var compilation = (CSharpCompilation) GetTestCompilation();

      var rewriter = new Rewriter(changeSomething: true);
      var tree = compilation.SyntaxTrees.First(); //first SyntaxTree is the one of class MyAssembly.Foo
      rewriter.Model = compilation.GetSemanticModel (tree);

      //first rewrite run
      var resultTree = rewriter.Visit (tree.GetRoot()).SyntaxTree;
      compilation = UpdateIfNecessary (compilation, rewriter, tree, resultTree);
      rewriter.Model = compilation.GetSemanticModel (resultTree);

      //just for demonstration; comment in to test behaviour when we are rewriting the class Bar -> in this case use Bar as constructor parameter in Foo
      //RewriteBar(rewriter, compilation, resultTree);

      //second rewrite run
      rewriter.Visit (resultTree.GetRoot());

      //now we want to compare the types...

      Console.WriteLine(rewriter.ParameterTypeFirstRun);
      Console.WriteLine(rewriter.ParameterTypeSecondRun);

      //=> types are *not* equal
      var typesAreEqual = rewriter.ParameterTypeFirstRun.Equals (rewriter.ParameterTypeSecondRun);
      Console.WriteLine("typesAreEqual:            " + typesAreEqual);

      //=> syntax references are not equal
      if(rewriter.ParameterTypeFirstRun.DeclaringSyntaxReferences.Any())
      {
        var syntaxReferencesAreEqual =
          rewriter.ParameterTypeFirstRun.DeclaringSyntaxReferences.First()
          .Equals(rewriter.ParameterTypeSecondRun.DeclaringSyntaxReferences.First());
        Console.WriteLine("syntaxReferencesAreEqual: " + syntaxReferencesAreEqual);
      }

      //==> other options??
    }

    private static CSharpCompilation UpdateIfNecessary(CSharpCompilation compilation, Rewriter rewriter, SyntaxTree oldTree, SyntaxTree newTree)
    {
      if (oldTree != newTree)
      {
        //update compilation as the syntaxTree changed
        compilation = compilation.ReplaceSyntaxTree(oldTree, newTree);
        rewriter.Model = compilation.GetSemanticModel(newTree);
      }
      return compilation;
    }

    /// <summary>
    /// rewrites the SyntaxTree of the class Bar, updates the compilation as well as the semantic model of the passed rewriter
    /// </summary>
    private static void RewriteBar(Rewriter rewriter, CSharpCompilation compilation, SyntaxTree firstSyntaxTree)
    {
      var otherRewriter = new Rewriter(true);
      var otherTree = compilation.SyntaxTrees.Last();
      otherRewriter.Model = compilation.GetSemanticModel(otherTree);
      var otherResultTree = otherRewriter.Visit(otherTree.GetRoot()).SyntaxTree;
      compilation = UpdateIfNecessary(compilation, otherRewriter, otherTree, otherResultTree);
      rewriter.Model = compilation.GetSemanticModel(firstSyntaxTree);
    }

    public class Rewriter : CSharpSyntaxRewriter
    {
      public SemanticModel Model { get; set; }
      private bool _firstRun = true;
      private bool _changeSomething;

      public ITypeSymbol ParameterTypeFirstRun { get; set; }
      public ITypeSymbol ParameterTypeSecondRun { get; set; }

      public Rewriter (bool changeSomething)
      {
        _changeSomething = changeSomething;
      }

      public override SyntaxNode VisitClassDeclaration(ClassDeclarationSyntax node)
      {
        node = (ClassDeclarationSyntax)base.VisitClassDeclaration(node);

        //remember the types of the parameter
        if (_firstRun)
          ParameterTypeFirstRun = GetTypeSymbol (node);
        else
          ParameterTypeSecondRun = GetTypeSymbol (node);

        _firstRun = false;

        //change something and return updated node
        if(_changeSomething)
          node = node.WithMembers(node.Members.Add(GetMethod()));
        return node;
      }

      /// <summary>
      /// Gets the type of the first parameter of the first method
      /// </summary>
      private ITypeSymbol GetTypeSymbol(ClassDeclarationSyntax classDeclaration)
      {
        var members = classDeclaration.Members;
        var methodSymbol = (IMethodSymbol) Model.GetDeclaredSymbol(members[0]);
        return methodSymbol.Parameters[0].Type;
      }

      private MethodDeclarationSyntax GetMethod()
      {
        return (MethodDeclarationSyntax)
          CSharpSyntaxTree.ParseText (@"public void SomeMethod(){ }").GetRoot().ChildNodes().First();
      }
    }

    private static SyntaxTree[] GetTrees()
    {
      var treeList = new List<SyntaxTree>();
      treeList.Add(CSharpSyntaxTree.ParseText(Source.Foo));
      treeList.Add(CSharpSyntaxTree.ParseText(Source.Bar));
      return treeList.ToArray();
    }

    private static Compilation GetTestCompilation()
    {
      var mscorlib = MetadataReference.CreateFromFile(typeof(object).Assembly.Location);
      var refs = new List<PortableExecutableReference> { mscorlib };

      // I used this to test it with a reference to an external assembly
      // var testAssembly = MetadataReference.CreateFromFile(@"../../../Demo.TypeSymbol.TestAssembly/bin/Debug/Demo.TypeSymbol.TestAssembly.dll");
      // refs.Add (testAssembly);

      return CSharpCompilation.Create("dummyAssembly", GetTrees(), refs);
    }
  }

  public static class Source
  {
    public static string Foo => @"

      // for test with external assembly
      //using Demo.TypeSymbol.TestAssembly;

      namespace MyAssembly
      {
        public class Foo
        {
          public Foo(Foo x)
          {
          }
        }
      }
    ";

    public static string Bar => @"
      namespace MyAssembly
      {
        public class Bar
        {
          public Bar(int i)
          {
          }       
        }
      }
    ";
  }
}