Controller was just an example. I remember at one point I wanted to inject a value, and its name was "Foo", but the DI loader (whatever it's called) kept wanting to turn that into "FooProvider". There was no way to say -- no, the name is just Foo! It's not a shorthand for some other thing!
And like I say, no way to check that you've fixed the problem except reloading your whole app and waiting for it to show you an error, or not.
Providers are really the only place where this is likely to happen. A FooProvider is an object that provides Foo to the dependency injector. So you tell Angular to provide Foo, and Angular creates the corresponding FooProvider for you. And what sets providers apart from services and factories, is that you can configure your FooProvider before the Foo gets injected, which is very useful, but you are suddenly talking to an object that you never created; Angular did.
By the way, Ruby on Rails does tons of this sort of thing, and goes a lot further. It automatically matches your Person class with the People table in your DB.
I just think that's a bad way for it to work. It should look for the thing by the name you give it and then find that thing, or not.
edit: This portion of a down thread comment captures my complaint well:
"In a sane framework, errors are meant to direct you to the cause, not simply to announce that something somewhere is written in a way that the framework doesn't like because of complex reason foo."
