I am testing Visual Studio 2015 with C# 6.0 but the language features are not working. In an MVC web application, the following code does compile:
if (!string.IsNullOrWhiteSpace(Model.Profile?.TypeName))
{
// More logic here...
}
However, when I run the application via Debug and IIS Express, I get the following error:
CS1525: Invalid expression term '.'
How do I enable these features?
This works in MVC 5 (tested 5.2.3), you just need to add the roslyn code dom Nuget package
Replacement CodeDOM providers that use the new .NET Compiler Platform ("Roslyn") compiler as a service APIs. This provides support for new language features in systems using CodeDOM (e.g. ASP.NET runtime compilation) as well as improving the compilation performance of these systems.
PM> Install-Package Microsoft.CodeDom.Providers.DotNetCompilerPlatform
https://www.nuget.org/packages/Microsoft.CodeDom.Providers.DotNetCompilerPlatform/
Well, I have MVC5 and recently installed VS 2015.
I've installed CodeDOM providers package, but it didn't help... But after that I realized, that package supports framework 4.5 only, while I have target framework set to 4.6 during tests - it works with 4.5 though...
So pay attention also to target framework. If you have 4.5 - just install package Microsoft.CodeDom.Providers.DotNetCompilerPlatform. But if you have 4.5.1-4.6 as a target, you will have to change in web.config section
<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.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=\"Web\" /optionInfer+"/>
</compilers>
</system.codedom>
For C#, just change type to:
type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
I was having this same problem in Visual Studio 2015. Another answer here alluded to the solution I used, but they incorrectly specified the fix and never gave clarification.
On the the Visual Studio menu, select Project and you should see the sub-item Enable C#6 / VB 14 if you are having this problem. Select this menu sub-item. It will download the correct packages from Nuget and install them. After this, restart Visual Studio and reload your solution.
I cannot verify if this will also fix the Project Properties > Build > Advanced > Language Version selection to C# 6, so you might want to check this as well after enabling C# 6 from the menu.
Including following the advice of installing the latest Microsoft.CodeDom.Providers.DotNetCompilerPlatform I also had to set my root Web.config system.codedom to this to finally get all of the errors in Visual Studio 2015 to go away:
<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=\"Web\" /optionInfer+"/>
</compilers>
</system.codedom>
Now restart Visual Studio and that should do it.
Visual Studio 2015 will also show an Enable C#6 / VB 14 in the Project menu with an ASP.NET web site / web application selected.
This will de facto install Microsoft.CodeDom.Providers.DotNetCompilerPlatform and Microsoft.Net.Compilers packages into your project and add appropriate tags into web.config file.
<compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.4.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:7 /nowarn:1659;1699;1701" />
<compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.4.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:15 /nowarn:41008 /define:_MYTYPE=\"Web\" /optionInfer+" />
compilerelement for the roslyn codeprovider msdn.microsoft.com/en-us/library/y9x69bzw(v=vs.110).aspx in the web.config? – rene