After installing the RTM version of VS2012 last week and upgrading my project, I noticed that my web site was broken. The real culprit seemed to be that Microsoft changed how bundling works (the process of combining and minifying resources like js script and css files) between the RC version and the RTM version. For an excellent background on what this feature can do for you, see this tutorial.

It turns out my real problem was with Kendo. They don't provide non-minified files in the trial version, so the new bundling mechanism wasn't including the minified assets, which meant the Kendo minified assets were getting stripped out when I was trying to run under debug. (Reference here). I was able to use the work-around offered on this thread, and things started working again.

However, there are a few wrinkles when using the bundling code, so I thought I'd capture my experiences here. For example:

• For 3rd party components that don't ship with non-minified assets, you need a better way around the default bundling strategy provided in the kendo article above. The solution provided in that thread of removing the min files from the ignore list will end up duplicating other assets that do provide both a minified and regular version of their assets while running in debug mode, e.g. jquery. There is a workaround for this, though: If you specify your bundle file's pattern with the {version} macro, then the bundling framework is smart enough to include just the one copy of the asset. If you use a wildcard in the pattern (as shown in the thread), you will get duplicate min and non-min versions of the asset when you render. Here is what your code should look like:

  
  bundles.Add(new ScriptBundle("~/bundles/jquery").Include(
       "~/Scripts/jquery-{version}.js"));
  

• When specifying a CDN location, right now, you can't use the {version} macro, so you end up with a hardcoded reference for your CDN link (1.7.1 in the sample) and a {version} macro for the non-CDN reference (which could be 1.7.1, 1.7.2, or anything else that exists in your solution). This means that when you update locally, you need to remember to keep those version numbers in sync. The CDN path could take the version you have locally and substitute it in the CDN path that you provide removing this requirement.
• In the tutorial, there is a fallback script that they recommend you write after your Scripts.Render statement so you can gracefully fall back to the local version if the CDN version doesn't load. It would be much better if that fallback code would be emitted for you when you call Scripts.Render.
• Speaking of CDN, it appears that there is a very tight coupling assumed between a bundle and a CDN path. In other words, you cannot include multiple assets in one bundle because the CDN path for the bundle assumes it is a reference to a specific file on the CDN. It would be better to have CDN paths be tied to each individual item in the bundle.
• Also relating to CDN support: The CDN path will only be used if you set bundles.UseCDN to true AND you either have BundleTables.EnableOptimization set to true or compilation debug set to false in your web.config. Granted, you probably only want to use the CDN when you are pushing to production, but while trying to test things out, I was doing it locally and this caught me by surprise. The 2 items should be independent of each other. If not, why even bother having the UseCDN property?

It seems that there is quite a bit of friction in the current version of the bundling framework. Fortunately, it resides in the Optimization assembly which can be upgraded independently of the entire MVC framework. I hope Microsoft releases an update very soon to overcome these obstacles. I have every reason to believe that they will since I'm seeing the author of this assembly answering tons of questions on StackOverflow.