Roslyn还出现这么低级的错误，不应该呀！

前几天对Dora.Interception作了简单的重构，想提供C#脚本来定义Interception Policy，毫无疑问微软提供的编译平台Roslyn使C#脚本化提供了支持。但是没有想到随便尝试了一个简单的功能就出现了问题，我个人觉得这应该是Roslyn的Bug。但是Roslyn经历了这么多次版本的迭代还出现如此低级的错误，实在有点说不过去。

闲话少说，我们现在通过几行简单的代码来重现这个Bug。我们创建了一个.NET Core 2.1的控制台应用，并添加针对NuGet包”Microsoft.CodeAnalysis.CSharp.Scripting“（版本2.8.2）的依赖。如下所示的是.csproj的完整定义。

<Project Sdk="Microsoft.NET.Sdk">
    <PropertyGroup>
        <OutputType>Exe</OutputType>
        <TargetFramework>netcoreapp2.1</TargetFramework>
        <AssemblyName>App</AssemblyName>
        <RootNamespace>App</RootNamespace>
    </PropertyGroup>
    <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
        <LangVersion>7.3</LangVersion>
    </PropertyGroup>
    <ItemGroup>
        <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Scripting" Version="2.8.2" />
    </ItemGroup>
</Project>

接下来我们编写了一段简单的程序。如下面的代码片段所示，我们只是采用脚本的形式创建了一个Foo对象并利用它创建出Bar对象，然后调用后者的Print方法而已。

namespace Scripting
{
    public class Foo { }
    public class Bar
    {
        public Foo Foo { get; }
        public Bar(Foo foo) => Foo = foo;
        public void Print() => Console.WriteLine(Foo);
    }

    class Program
    {
        static async Task Main(string[] args)
        {
            var options = ScriptOptions.Default
                .AddReferences(typeof(Program).Assembly)
                .AddImports("Scripting");

            //Success
            await CSharpScript
               .Create("var bar = new Bar(new Foo());", options)
               .ContinueWith("bar.Print()")
               .RunAsync();
        }
    }
}

这段代码是没有问题的，运行之后Print方法输出的结果可以正常出现在入下所示的控制台上。

接下来我们将“var bar = new Bar(new Foo());”这行代码按照如下的方式拆分成两行执行。

class Program
{
    static async Task Main(string[] args)
    {
        //Fail
        await CSharpScript
            .Create("var foo = new Foo();", options)
            .ContinueWith("var bar = new Bar(foo);")
            .ContinueWith("bar.Print()")
            .RunAsync();
    }
}

在此运行该程序后出现如下所示的“Microsoft.CodeAnalysis.Scripting.CompilationErrorException”异常，并提示“cannot convert from 'Scripting.Foo [App, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]' to 'Scripting.Foo [c:\users\jinnan\Source\Repos\App\App\bin\Debug\netcoreapp2.1\App.dll]”。

如下所示的是完整的错误信息：

Unhandled Exception: Microsoft.CodeAnalysis.Scripting.CompilationErrorException: (1,19): error CS1503: Argument 1: cannot convert from 'Scripting.Foo [App, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]' to 'Scripting.Foo [c:\users\jinnan\Source\Repos\App\App\bin\Debug\netcoreapp2.1\App.dll]'
   at Microsoft.CodeAnalysis.Scripting.ScriptBuilder.ThrowIfAnyCompilationErrors(DiagnosticBag diagnostics, DiagnosticFormatter formatter) in /_/src/Scripting/Core/ScriptBuilder.cs:line 104
   at Microsoft.CodeAnalysis.Scripting.ScriptBuilder.CreateExecutor[T](ScriptCompiler compiler, Compilation compilation, Boolean emitDebugInformation, CancellationToken cancellationToken) in /_/src/Scripting/Core/ScriptBuilder.cs:line 89
   at Microsoft.CodeAnalysis.Scripting.Script`1.GetExecutor(CancellationToken cancellationToken) in /_/src/Scripting/Core/Script.cs:line 359
   at Microsoft.CodeAnalysis.Scripting.Script`1.CommonGetExecutor(CancellationToken cancellationToken) in /_/src/Scripting/Core/Script.cs:line 343
   at Microsoft.CodeAnalysis.Scripting.Script`1.TryGetPrecedingExecutors(Script lastExecutedScriptInChainOpt, CancellationToken cancellationToken) in /_/src/Scripting/Core/Script.cs:line 407
   at Microsoft.CodeAnalysis.Scripting.Script`1.GetPrecedingExecutors(CancellationToken cancellationToken) in /_/src/Scripting/Core/Script.cs:line 370
   at Microsoft.CodeAnalysis.Scripting.Script`1.RunAsync(Object globals, Func`2 catchException, CancellationToken cancellationToken) in /_/src/Scripting/Core/Script.cs:line 459
   at Scripting.Program.Main(String[] args) in c:\users\jinnan\Source\Repos\App\App\Program.cs:line 31
   at Scripting.Program.<Main>(String[] args)

这是我提交的issue链接：https://github.com/dotnet/roslyn/issues/28803#issuecomment-407894956