Upgrading to Visual Studio 2015 renders intellisense broken for project

Question

I've been through a lot of similar issues, but could not find anything that worked for me.

I'm upgrading my IDE from the VisualStudio for Web (v10) to Visual Studio 2015 (v14, I guess) Community Edition. The main project that I'm trying to use on the new IDE is a MVC 5 (5.2.3), with EF 6.1 (6.1.3) and a bunch of other stuff.

Problem is: When opening the project on the new IDE, everything looks fine (it even compiles and work). I got the MVC context menu working on the project explorer (showing the "Add Controller..." and "Add View..." when appropriate). Only (really annoying) thing is the Razor Intellisense.

When I do open a View file (.cshtml) I receive warnings on several helpers, some of the "using" are greyed out (even though they're supposed to be needed) and the @model myModel is shown like everything after the @model directive is not razor (it's treated like HTML by the intellisense coloring).

What I've already found and tried:

1. • I've already tried to clear the UserData from the vs (devenv /ResetUserData)
2. • I've already tried to run the VS2015 in safe mode
3. • I've already tried to run VS2015 as Administrator
4. • I've already tried to set the Project's target framework to 4.5.1 (used to be 4.5)
5. • I've already tried to open the project on Visual Studio Community 2013 saving it there before trying to use it on VS2015.

When creating another MVC project from the VS2015, everything works fine.

Here's an example of the annoying issue:

Answer 1

Ok, finally got it. Posting what I found out believing it may help someone else:

1. What seems to cause the problem mentioned is the fact that the project was created on an old MVC version (with older Razor, EF, etc).

2. As stated in this answer: Visual Studio 2015 Razor View MVC Types not recognized, VS2015 tools may not work for older MVCs.

3. The solution is to update all your packages to [at least] the minor versions accepted on newer MVC (5?). To do so you can use the list in this website: http://www.asp.net/mvc/overview/releases/how-to-upgrade-an-aspnet-mvc-4-and-web-api-project-to-aspnet-mvc-5-and-web-api-2.

4. Once everything is up-to-date, open the web.config files located on root of your application and on the Views folder. In there, you will probably find some references to the older versions of MVC and Razor. Update those versions values (all of them) to match the updated versions of your packages (you may create a new empty MVC project on the new Visual Studio and check for those values as a hint of what they should be).

   This step is the catch! Since, even if you update you project's packages, some web.config references may still mention the original versions.

5. Clean the solution (Build > Clean Solution) and close the project. Reopen and compile it. Now [hopefully] everything should be working fine.

[Edit]

6. One more thing: If your project was also updated from Framework 4.5 to 4.5.1 during this IDE transition, you should also install a NuGet package called "Microsoft.CodeDom.Providers.DotNetCompilerPlatform" (as stated in https://support.microsoft.com/en-us/kb/3025133).