Hi Nikolai,

I think the incremental (first) version is the best one since you can see
which bugs are worked around by us and which are fixed per release at a glance.

But really it doesn't matter much which.

> Second solution looks too verbose for me, but with first solution on
> long chain of versions it will be very hard to manage which changes we
> have in newest package.

I hope we won't have a long chain of cumulative Rust versions in Guix.  I know
that Rust upstream likes to do this chain of Rust1 -> Rust2 -> Rust3 -> Rust4
but that's not really scalable - especially since even one Rust takes a day
to compile.  We should try to get mrust [1] to work and use it to compile just
the newest Rust.  If it doesn't work we can still fall back to one of the
other ways later.

(What Mozilla recommends is we compile Rust1, use Rust2 to compile Rust3, use
Rust3 to compile Rust4, likewise for each new release)

[1] https://github.com/thepowersgang/mrustc