Strange automatic namespace imports in my Razor views - asp.net-mvc

Question

Today I noticed that e.g. "System" and "System.Web.Security" are imported in all my razor views, although I did not actively import them. I checked:
#using directive
web.config (EDIT: also global web.config)
AddGlobalImport
EDIT:
It seems these namespace imports are hardwired in the Razor Source Code
https://github.com/ASP-NET-MVC/aspnetwebstack/blob/master/src/System.Web.WebPages.Razor/WebPageRazorHost.cs
private WebPageRazorHost()
{
NamespaceImports.Add("System");
NamespaceImports.Add("System.Collections.Generic");
NamespaceImports.Add("System.IO");
NamespaceImports.Add("System.Linq");
NamespaceImports.Add("System.Net");
NamespaceImports.Add("System.Web");
NamespaceImports.Add("System.Web.Helpers");
NamespaceImports.Add("System.Web.Security");
NamespaceImports.Add("System.Web.UI");
NamespaceImports.Add("System.Web.WebPages");
NamespaceImports.Add("System.Web.WebPages.Html");
// ...
}
It also seems that I can't disable these by setting a "clear" at the beginning of my web.config:
<system.web.webPages.razor>
<host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<pages pageBaseType="System.Web.Mvc.WebViewPage" >
<namespaces>
<clear />
<add namespace="System.Web.Helpers" />
<add namespace="System.Web.Mvc" />
<add namespace="System.Web.Mvc.Ajax" />
<add namespace="System.Web.Mvc.Html" />
<add namespace="System.Web.Routing" />
<add namespace="System.Web.WebPages" />
</namespaces>
</pages>
</system.web.webPages.razor>
So this issue might be unfixable unless Razor source is changed.

Answer 1

it is common , because it is registered in overall web config file at following location :
systemroot\Microsoft.NET\Framework\versionNumber\CONFIG\Web.config
it is registered like this :
<pages>
<namespaces>
<add namespace="System" />
<add namespace="System.Collections" />
<add namespace="System.Collections.Generic" />
<add namespace="System.Collections.Specialized" />
<add namespace="System.ComponentModel.DataAnnotations" />
<add namespace="System.Configuration" />
<add namespace="System.Linq" />
<add namespace="System.Text" />
<add namespace="System.Text.RegularExpressions" />
<add namespace="System.Web" />
<add namespace="System.Web.Caching" />
<add namespace="System.Web.DynamicData" />
<add namespace="System.Web.SessionState" />
<add namespace="System.Web.Security" />
<add namespace="System.Web.Profile" />
<add namespace="System.Xml.Linq" />
</namespaces>
</pages>
EDIT:
following is from an SO answer here:
In Preview 1 Razor used the WebForms namespaces config section. However in the Beta there is a new config section that is seperate from the WebForms one. You will need to add the follwing to your web.config file (or just start with a brand new project from the template):
<configSections>
<sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
<section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
<section name="pages" type="System.Web.WebPages.Razor.Configuration.RazorPagesSection, System.Web.WebPages.Razor, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
</sectionGroup>
</configSections>
<system.web.webPages.razor>
<pages pageBaseType="System.Web.Mvc.WebViewPage">
<namespaces>
<add namespace="MyCustomHelpers" />
</namespaces>
</pages>
</system.web.webPages.razor>

Answer 2

I ran across this question while answering another one (Removing System.Web.UI from a Razor view). Below is a copy of my answer. It may be useful.
I'm not sure if this is what you're after, but I did a quick experiment. I think it works.
I extended the MvcWebRazorHostFactory a bit. The new factory basically passes along the host created by the base class, but removes the namespace first.
This is the class:
namespace TestCode
{
using System.Web.WebPages.Razor;
using System.Web.Mvc;
using System.Web.Mvc.Razor;
public class CustomWebRazorHostFactory : MvcWebRazorHostFactory
{
public override WebPageRazorHost CreateHost(string virtualPath, string physicalPath)
{
WebPageRazorHost host = base.CreateHost(virtualPath, physicalPath);
host.NamespaceImports.Remove("System.Web.UI");
return host;
}
}
}
Then I changed web.config to use my factory instead of the standard one:
<system.web.webPages.razor>
<!--<host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />-->
<host factoryType="TestCode.CustomWebRazorHostFactory" />
Bingo!

Answer 3

So the answer is: In Razor views some namespaces are always imported. This can't be disabled in configuration because it is hardwired in the code. These namespaces are:
System
System.Collections.Generic
System.IO
System.Linq
System.Net
System.Web
System.Web.Helpers
System.Web.Security
System.Web.UI
System.Web.WebPages
System.Web.WebPages.Html
I am not 100% sure that this is the complete answer, but as long as there is no opposing comment I will accept it.