On Sat, May 01, 2021 at 11:20:51AM +0200, Hartmut Goebel wrote:
> Hi Ludo,
>
> Am 30.04.21 um 12:45 schrieb Ludovic Courtès:
>
> > Uh. More generally, Rust packages kinda create a “shadow dependency
> > graph” via #:cargo-inputs & co., which breaks all the tools that are
> > unaware of it. It was discussed several times on this list, and
> > apparently it’s unfortunately unavoidable at this time. :-/
>
> Maybe we can get rid of #:cargo-inputs at least:
>
> guix/build-system/cargo.scm says: "Although cargo does not permit cyclic
> dependencies between crates,
> however, it permits cycles to occur via dev-dependencies"
That I don't remember, but it would make it easier.
> So we could change #:cargo-inputs into normal inputs and get at least part
> of the dependencies right.
>
> I'm aware of the "special treatment" of cargo-inputs. Anyhow we could apply
> the following changes to the cargo build-system:
>
> *
>
>The cargo build-system copies the "pre-built crate" (more on this
>below) into a new output called "rlib" or "crate". There already is
>a phase "packaging" which only needs to be changed to use the other
>output.
>
> *
>
>All of today's #:cargo-inputs will be changed into normal inputs
>using the "rlib/crate" output. (To avoid duplicate assoc-rec keys we
>might need to change the name/keys, but this should be a minor issue.)
>
> *
>
>If required, the cargo build-system can easily identify former
>#:cargo-inputs by being inputs from a "rlib/crate" output.
>
> Benefits up to here:
>
> * The dependency graph would be much more complete - although
>"#:cargo-development-inputs" would still be missing.
This is the biggest one IMO.
> * Package transformation options would work -again except for
>"#:cargo-development-inputs".
IIRC they're pulled in as (package-source rust-foo-0.x) so some of the
transformations should work (I would assume).
> * If(!) we actually manage to make cargo pick "pre-built" crates,
>package definition will already be adjusted to use them.
And cut down on some of the big build times.
> |Drawbacks up to here:|
>
> * ||Since the "packaging" phase copies the source, there is not much
>benefit in having a "rlib/crate" output yet. Actually, when a
>"rlib/crate" output needs to be build, the user will end up with two
>copies of the source (one from the git-checkout, one from packaging)
The benefit of copying the source is that in theory you should be able
to set $GUIX_ENVIRONMENT/share/cargo/registry (or whatever) as a cache for
crates.io when developing, so if you want different features from the
crates you won't have to download the source, it would already be cached
locally.
> About "pre-built" crate: Given the many possible ways to build crates (e.g.
> switching on and off "features", different crate types), we might never be
> able to provide pre-built packages for all cases. Thus we might end up
> always providing the source, even if we manage to make cargo pick of
> pre-built artifacts.
Right now we use the 'default' feature set, which seems to be the
default for most crates when they're used.
> About the output name: Rust has a notion of "rlib" (a specialized .a file),
> which seems to be the pre-built artifacts we are seeking. Thus the proposed
> name.
>
> WDYT?
>
> --
> Regards
> Hartmut Goebel
When I last touched it I started from rust-apps.scm (or rust-minisign)
and tried transitioning as much as possible, but doing even just the
cargo-inputs would be a very good start.
--
Efraim Flashner אפרים פלשנר
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