Can you give an example of what it simplifies/solves?

The bundle best practices suggest sub-directories for the vendor and category of the bundle. The FOS UserBundle employs this; however, the Doctrine extensions would require the specific vendor/category directory to be defined in the kernel's registerBundleDirs() array. This patch allows you to keep just "Bundle" in that array, and if you have a bundle within "Bundle\FOS", it can still be detected.

I think it's a bit much to require the user to register each vendor/category directory in registerBundleDirs() otherwise, no?

I am not sure this should be in the DI extension, instead if should be in your Kernel. You can write some code to easily dynamically add all the directories. I think it is better to have less code in Symfony2 for us to maintain and to be more explicit in the configuration side.

public function registerBundleDirs()
{
    $dirs = array();
    $bundles = glob(__DIR__.'/../src/Bundle/*');
    foreach ($bundles as $dir) {
        $info = pathinfo($dir);
        $dirs['Bundle\\'.$info['filename']] = $dir;
    }
    return $dirs;
}

If my own bundle needed such a thing, I'd still do it right in the extension. Otherwise, the best solution is just to make in clear in the documentation that any directory path holding a bundle (be it src/Bundle, /src/Bundle/Vendoror even /src/Bundle/Vendor/Category) must be explicitly defined in registerBundleDirs(). That was my alternative solution to get FOS\UserBundle working while this pull request sat in limbo.

I wouldn't encourage anyone to use your snippet above, though. Adding all sub-directories like that will help bundles that are grouped by only a vendor path. It does nothing for categorized, vendor-grouped bundles, and will likely create garbage paths for non-vendor-named bundles (e.g. src/Bundle/FooBundle).

This patch sort of conflicts with pull request 264, i can integrate parts of it but automatic matching will be deprecated in favor of an explicit approach anyways as discussed in the Symfony IRC meeting 3 weeks ago.

I can do more work on it this week and finalize it.

yeah ... 264 seems to be the way to do things down the road.

I wish I had seen 264 before doing this :)

I agree that it's a better approach; closing this one.