VS2015 新Web项目(C#6)出现CS1617错误的解决

VS2015新增了对C#6的支持.

在新的Web项目模板中通过引入nuget包Microsoft.CodeDom.PRoviders.DotNetCompilerPlatform:1.0.0并在web.config中添加

  <system.codedom>    <compilers>      <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701" />      <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=/&quot;Web/&quot; /optionInfer+" />    </compilers>  </system.codedom>

来提供Razor的C#6.0支持(旧项目也可以通过自己添加来获得支持)

但是在当你修改了目标框架(例如从4.5升级到4.6)之后, 网站将会无法开启并提示

[没有相关的源行]

C:/Program Files (x86)/IIS Express> "C:/Windows/Microsoft.NET/Framework/v4.0.30319/csc.exe" /t:library /utf8output /R:"C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary asp.net Files/vs/...Microsoft (R) Visual C# Compiler version 4.6.0081.0for C# 5Copyright (C) Microsoft Corporation. All rights reserved.This compiler is provided as part of the Microsoft (R) .NET Framework, but only supports language versions up to C# 5, which is no longer the latest version. For compilers that support newer versions of the C# programming language, see http://go.microsoft.com/fwlink/?LinkID=533240error CS1617: 选项“6”对 /langversion 无效；必须是 ISO-1、ISO-2、3、4、5 或 Default

查看web.config中的配置, 发现已被自动修改为(似乎一般是改cs不改vb, 往低了改会连vb一起改)

  <system.codedom>    <compilers>      <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701">        <providerOption name="CompilerVersion" value="v4.0"/>      </compiler>      <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.VisualBasic.VBCodeProvider, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=/&quot;Web/&quot; /optionInfer+">          <providerOption name="CompilerVersion" value="v4.0"/>      </compiler>    </compilers>  </system.codedom>

而这是无法正常工作的, 需要手动修改为最初的结果

已反馈至https://connect.microsoft.com/VisualStudio/feedback/details/1607466

2015/07/31: 微软已确认