Hi.
A few days ago I found PHPStorm plugin that makes code completion work for services fetched from container: pulyaevskiy/phpstorm-phpdi. It's pretty simple, but does it's job well.
No more _@_var annotations needed, it just works (if you using php5.5 syntax for defining services).

I find it very useful, so maybe it is worth to be added to the documentation?

It is not a PR adding link to the docs cause I'm not sure it is a good idea. Maybe @pulyaevskiy should give his agreement at first? It is published under MIT license, but I'm not good at software license types.