CODEWITHSUNDEEP
.netasp.net-mvcasp.net-mvc-5web-configcodedom
MarioDS
MarioDS

Reputation: 13063

What exactly does <system.codedom>/<compilers> do in web.config in MVC 5?

I am about to migrate a bunch of projects from .NET 4.0 + MVC 3 to .NET 4.5.2 + MVC5.

To make this easier, I've created a new blank MVC project to compare DLL references and some other stuff such as web.config.

In the latter, the following entries are generated by Visual Studio:

<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>

But I don't know what this does exactly. The MVC 3 projects don't contain these parts. My understanding is it has something to do with Roslyn?

Upvotes: 42

Views: 28682

Answers (2)

Janis Veinbergs
Janis Veinbergs

Reputation: 6988

These lines are added whenever you install Microsoft.CodeDom.Providers.DotNetCompilerPlatform nuget package.

It is for improved performance whether precompiling or dynamically compiling asp.net app, by using "Roslyn" compilation

In my case precompile went from 34mins to 13mins:

Upvotes: 1

Jochen
Jochen

Reputation: 1488

These settings are used for dynamic compilation. They can be safely removed from the web.config if you do pre-compilation and only put the compiled assemblies on the webserver.

See also The impact of multiple compiler definitions in system.codedom in web.config

Upvotes: 53

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