[Pkg-rust-maintainers] Rust for Linux and host-only libraries

[Fabian Grünbichler]

On April 19, 2024 8:44:12 PM GMT+02:00, Miguel Ojeda <miguel.ojeda.sandonis at gmail.com> wrote:
>On Fri, Apr 19, 2024 at 8:13 PM Fabian Grünbichler
><debian at fabian.gruenbichler.email> wrote:
>>
>> Yes, all crates packaged by the Rust team (and most packaged for consumption by other packages/as build-deps by people outside of the team) ship their (patched for distro use) sources in a subdir there. The patches (except for wholesale exclusions of bundled C code and similar things, which is done via orig tarball repacking) are also shipped there, so the delta is easily reviewable. The whole directory structure can be used as (partial) drop-in for crates.io by configuring cargo accordingly (in Debian packaging this is done by a cargo wrapper shipped in /usr/share/cargo/bin/cargo, but that one is probably not suitable as-is for kernel stuff - it or rather its output might serve as an example for the needed cargo config runes though ;))
>
>Thanks for the quick reply!
>
>I see -- in principle, we only need the sources, i.e. we would not
>compile the crates using Cargo. Are the patches applied to the sources
>already, or are they applied by that cargo wrapper you mention at
>build time? (Well, assuming users should use the patched versions).

No, the patches are already applied in the source files shipped by librust-xxx-dev, if there are any. The cargo wrapper takes care of other things, like instructing cargo to use the packaged sources and setting rustflags and similar options. You should be able to use the same sources with manual rustc invocations without cargo or our wrapper just fine :) 

There's a bit of peculiarity around the versioning - the librust-.. packages provide all the semver prefixes of their version as well, so you can express "I want crate X in a semver compatible version of at least 2.3" via a versioned dependency (by depending on librust-x-2-dev with a version of at least 2.3), but also the more restricted variants (e.g., X in some 2.3.n version, or a specific 2.3.4 version, by depending on librust-2.3-dev resp. librust-2.3.4-dev). Normally, the actual package providing all of those is librust-X-dev, except when we need to package more than one version of X, then there might be a librust-X-dev in version A (providing all the semver prefixes of A), and another package librust-X-B-dev, where B is the shortest semver-breaking prefix of a semver incompatible version older than A (providing all semver prefixes of that version). A might be 2.3.4 and B 1 (with B's full version being 1.2.0, for example). Most of that won't be relevant for you - except that you want to depend on e.g. librust-syn-1-dev if you want syn 1.x, even if the actual "real" package is called librust-syn-dev, as the latter might also contain syn 0.x or 2.x in other distros/releases. Hope this was not too confusing ;)