I looked into this once;
I found a Rust compiler written in OCaml on the web.
There should be a path from that compiler to the current version of Rust.
The problem lies in the fact that the entire "1.9 build 1.10 builds 1.11"
spiel only become the official policy of the Rust project recently.

disclaimer: the following is how I interpreted my communications with
the rust community. My apologies to anyone involved for any inaccuracies
and/or misrepresentations.

This means that you could be looking at individual commits, as before this,
I believe nightlies (snapshots) were used to compile the Rust compiler.

So, to ad to Alex' point, we would also need to expend (one-time) effort to
find this 'bootstrap-path' from the OCaml-based compiler to a more recent
rustc.

In my admittedly little amounts of experience, the people working on rust
were not really seeing the problem with the current state of affairs, so
good luck getting support with some arcane issues one might encounter
packaging these ancient versions of rustc.

To quote kibwen from [1]:
"We can determine exactly how many builds you'd need by looking at the
master snapshot file:
https://github.com/rust-lang/rust/blob/master/src/snapshots....
<https://github.com/rust-lang/rust/blob/master/src/snapshots.txt>

According to this, there have been 290 snapshots in total. And keep in mind
that you would also need to rebuild LLVM quite a few times as well during
this process, as Rust has continually upgraded its custom LLVM fork over
the years."

Not sure if all this is worth the effort...

- Jelle


[1]: https://news.ycombinator.com/item?id=8732669


2016-07-29 17:34 GMT+02:00 Alex Griffin <a@ajgrf.com>:

> On Fri, Jul 29, 2016, at 10:16 AM, Ludovic Courtès wrote:
> > Do you know what’s Rust’s bootstrapping story is?  Can we reasonably
> > expect to bootstrap it from source, using a series of previous Rust
> > versions, or using an alternative implementation?
>
> Yes, Rust 1.10 builds with the previous stable release (1.9) for the
> first time. So we will only need one binary to bootstrap Rust. Although
> this will quickly require a long chain of builds because Rust releases
> every 6 weeks and 1.11 is only guaranteed to build with 1.10, etc.
>
> So after only two years we may need to compile like 17 different
> releases to get the current version.
> --
> Alex Griffin
>
>