It took me a while to realize and, to be honest, I ignored the upgrade report when opening Umbraco projects in VS15. They clearly state:

ASP.NET MVC 4 projects have limited functionality in Visual Studio Next. Commands such as Add Controller, Add View, Add Area, and Go to View/Controller are not available. Intellisense for Razor (CSHTML and VBHTML) files is limited to HTML markup.

However, there is a bug in Umbraco currently, if you have a macro that contains a SurfaceController and in the SurfaceController you do ModelState.AddModelError("SomeField", "Some message"); then it will fail. This is fixed in 7.3.0.

I'm about to write a blog post on how to upgrade an Umbraco project to MVC5. If you use NuGet then it should be as "easy" as:

Uninstall-Package Microsoft.AspNet.WebPages.Administration
Uninstall-Package Microsoft-Web-Helpers

these may fail if you don't have these packages installed, so ignore errors from that

Uninstall-Package Microsoft.AspNet.Mvc.FixedDisplayModes -Force

don't forget the -Force

Update-Package Microsoft.AspNet.Mvc
Install-Package ClientDependency-Mvc5
Update-Package Microsoft.AspNet.WebApi

You might also need to install WebHelpers if you currently have it installed:

Install-Package Microsoft.AspNet.WebHelpers

Which then most likely also requires:

Install-Package Microsoft.AspNet.WebPages.Data

Lastly, you will need to go to Views\web.config and replace all instances of 2.0.0.0 with 3.0.0.0 and all instances of 4.0.0.0 with 5.2.3.0.

Yeah "easy", right? ;-)

It's a bit shitty but Microsoft in their infinite wisdom decided that they don't support MVC4 any more in VS15 so either use VS13 or upgrade to MVC5 if you want the squiggles to go away (intellisense still works but everything is marked as being "wrong").

Thanks Sebastiaan, that works! No more squiggles!

Is it not possible to add MVC4 support?

I have a bunch of old projects, that I don't really want to upgrade to MVC5.

@Søren It's simply not supported by MS:

ASP.NET MVC 4 projects have limited functionality in Visual Studio Next. Commands such as Add Controller, Add View, Add Area, and Go to View/Controller are not available. Intellisense for Razor (CSHTML and VBHTML) files is limited to HTML markup.

Related topic here: https://our.umbraco.org/forum/developers/razor/66923-viewswebconfig-namespaces-not-available-in-views-in-visual-studio-2015-text-editor#comment-232554

Posting for convenience.

@Seb, thanks for putting this all together. FWIW though it's not working for me. Still getting red squigglies but it's likely something I didn't do properly.

I'll try again another time :)

After installation of Umraco with MVC selection

1- If the following lines of code give a warning:        Assuming assembly reference 'system.web.mvc version = 5.2.3.0 culture = neutral, publickeytoken = version = 5.2.4.0

   Requirements:

   If the Microsoft.AspNet.Mvc package is version 5.2.4 or higher    Remove the installed package from the Nuget Package Manager by selecting the dependency options,    Then, installing Install.Package Microsoft.AspNet.Mvc -Version 5.2.3 will eliminate the problem.

2- After doing this step, you will need to Clean Solution and then Build it. 3- In the build process, it can give an error message as follows.

   Analyzer 'Microsoft.CodeAnalysis.CSharp.Analyzers.FixAnalyzers.CSharpFixerWithFixAllAnalyzer' threw an exception of type    Solution from Console    From the following URL    https://www.nuget.org/packages/microsoft.codeanalysis.analyzers

   Microsoft.CodeAnalysis.Analyzers 2.6.3 The Nuget Package will be installed to correct the corresponding error.

   Then you will need to Clean the project and then Clean again.

That's all

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