Using Latest C# Language Features (Roslyn)

The library by default uses the .NET Runtime built in CSharp code provider which supports only C# 5.x. It's possible to use later versions of C# by explicitly adding the new .NET Compiler platform libraries to the host project and explicitly providing the CSharpProvider. We don't provide this in the box because the Roslyn compiler package is very large (17megs) so we provide an opt-in mechanism that lets you decide if you need the newer language features and extra deployment requirements for your host application.

To add C# 7.x support:

• Add Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider Nuget Package to your Project
• Add <system.codedom> section to host app's app.config
• Provide CSharpCodeProvider to RazorEngine or HostContainer

Here are the required app.config settings that ensures that the compiler binaries can be found:

<configuration>
	<appSettings>
		<add key="aspnet:RoslynCompilerLocation" value="roslyn"/>
	</appSettings>
	<system.codedom>
		<compilers>
			<compiler language="c#;cs;csharp" extension=".cs"
				type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
				warningLevel="4" compilerOptions="/langversion:default /nowarn:1659;1699;1701"/>
			<compiler language="vb;vbs;visualbasic;vbscript" extension=".vb"
				type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
				warningLevel="4" compilerOptions="/langversion:default /nowarn:41008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+"/>
		</compilers>
	</system.codedom>
</configuration>

To use the compiler with your Razor code use one of the following approaches to pass the CSharpCodeProvider:

Basic RazorEngine

var cs = new Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider()
var engine = new RazorEngine(cs);

Using a HostContainer

var host = new RazorFolderHostContainer();
host.CodeProvider = new Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider();

Does not work with Out of Process Hosting

This approach of providing the CSharp code provider does not work with AppDomain loading of the Razor engine in host containers. For AppDomain loaded instances only the stock C# 5 provider is used.