Re: Specifying rust version

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hello,

Efraim Flashner <efraim@flashner.co.il> writes:

> On Mon, Dec 26, 2022 at 09:00:40AM +0000, phodina wrote:
>> Hi,
>>
>> the documentation for 'cargo-build-system' [1] refers to parameter
>> '#:rust' which allows user to specify the Rust compiler version.
>> However, I've found this commit
>> 9635119a61a9ab1b023558727fcdf1816fdc7fc6 from Maxim which makes all
>> 'rust-.*' definitions private.  Is there a way to specify newer Rust
>> compiler? Something like 'rust-next'?  The package requires version
>> 1.62 but the current is 1.60. Also both version are already defined.
>> What's missing is just way to select them.
>>
>> [1] https://guix.gnu.org/manual/en/html_node/Build-Systems.html
>>
>
> I checked gnu/packages/rust.scm and it looks like the rust packages
> aren't hidden but actually not exported. If they were just hidden then
> you could still do `#:rust ,rust-1.62`. Since they're actually not
> exported you need to use the not-really-supported `@@` to refer to that
> variable, so you'd have to use something like:
> #:rust ,(@@ (gnu packages rust) rust-1.62)

Normally only the newest released Rust version is supported by upstream,
so what we should do is add a newer rust and use it by default.

The reasons previous rust versions are not exported is because they
aren't intended to be used by applications; they are built using
'--stage=1' to speed up compilation, which creates slower binaries and
may expose ABI stability problems (*if I remember the rust people's
explanation correctly).

When adding new version of rust, we move all the tests and final rust
version specifics to the leaf (last) rust version, and keep the
intermediary rusts minimal (no test, no tools, stage=1, etc.)

> Given how it would be useful to have access to newer rust versions I
> think it'd be worthwhile to make a post in guix-devel about making the
> newer versions of rust use define-public but be hidden, so they can be
> used as expected for the #:rust keyword.

It's typical that build system or services expose a way for the user to
use a variant of a package, but in the case of rust, I don't think it
should be advertised as a way to use different rust versions (given only
the last version is supported by upstream, e.g. sometimes fixing CVEs).

-- 
Thanks,
Maxim