[bug#42179] [PATCH] gnu: Add racer.

[John Soo]

Hi Jakub,

Sorry I am late to respond. 

> How about we use the source of rust itself for the rustc-ap packages?
> That way, updating rustc won't actually ever break because of RUSTC_BOOTSTRAP,
> since the use of the unstable features comes from the same source of
> truth that will actually compile them.

I like the idea of keeping racer up to date with rust. Do you think making 
racer an output of rust would be good or is a separate package depending on 
rust a better option?

Thanks!

John