The birth of a package manager
ochagavia.nl
ochagavia.nl
> One interesting avenue of future work is to try to replace libsolv by a solver written in Rust, such as PubGrub. That way we could get rid of a bunch of unsafe code we are using to interface with libsolv through Rust’s FFI.
For people who would be interested in learning more, check out this conference presentation: https://youtu.be/XyJpYFnl18U
Using pubgrub in cargo is something we talk about on a regularly basis. Its our equivalent of rustc chalk or polonius: we keep limping along, always finding a new hack to extend the life of the current package resolver due to the large lift to change out the resolver but also knowing how much the current one slows us down and holds us back.
I'm excited for any forward movement on pubgrub in any related project.
And thanks for linking a PackagingCon talk – I am actually the an organizer of that conference and happy to report that it's coming back this year in October (https://packaging-con.org has the details).
https://nex3.medium.com/pubgrub-2fb6470504f
She invented this for Dart's package manager (pub), which is where the name comes from.
I've never looked too deeply into how conda works because I'm not that into Python, but I guess I should. It seems there are some valuable general lessons here— I wish that more package managers, and in particular, Nix, maintained more version combinations in their repos. Searching through Nixpkgs commits to find compatible versions of things because you have to rely on the implicit versioning of the monorepo sucks.
Adding dependency resolution to Nix as it stands would normally add a big performance cost. Something like this would help with that problem a lot, and Nix already usually runs with a persistent daemon. Maybe a similar technique could fit in well here.
We are also quite curious to learn more about the Nix approach. Building packages is still a bit too painful / annoying in the conda ecosystem, which is something we really want to fix, and I think we can learn a lesson or two in the Nix ecosystem.
And by the way, the conda ecosystem is not at all Python specific. It's a common misconception, but they are all general binary packages and can be used for Ruby, R, Rust, C++, Zig, ... whatever – just like Nix. Rattler, mamba and conda all handle them the same nice way.
> Searching through Nixpkgs commits to find compatible versions of things because you have to rely on the implicit versioning of the monorepo sucks.
I get what you're saying, but I gave up on thinking of Nix/Nixpkgs in terms of "package management". It's much closer to a build system, like GNU Make; rather than, say, APT/Yum.
When it comes to versions of things in Nixpkgs: most things are defined as a function of other things; i.e. the arguments to that function are (roughly) its "dependencies". If we want some different version, we can call those functions with different arguments (or use the various `override` helpers included in their return values). Once we've overridden the things we care about, we can usually take the fixed-point/closure of that package set (whether it's the whole of Nixpkgs, or just e.g. python3Packages, or whatever); that way, our changes get propagated through all of the function calls to ensure everything's referencing our versions. Admittedly, this can be quite tedious!
It's a huge limitation for many reasonable ways that people want to use Nix. It's a shortcut that Nix has gotten away with, not a superior approach. Look at the machinery mach-nix implements with a cached database of PyPi and how it has to scan across different Nixpkgs revisions just to automatically choose compatible versions of deps when it does its code generation for a clear illustration.
There are lots of source-based package management systems which rely on a mix of implicit versioning based on what happens to be exist under an unversioned name in the monorepo and explicit versioning, Gentoo Portage for example.
There's no reason that we couldn't have either
a. a complement to Nixpkgs which serves as a record of which build recipes have successfully built what versions, and what versions their deps were at
b. richer metadata in Nixpkgs about versions that can be used to support multiple versions of same-named packages in the repository, and a smarter callPackage that uses those version constraints to choose, when necessary, which versions of dependencies to put into scope when calling a package (yes, I know there is ongoing work to remove callPackage, or at least explicit invocations of it)
Hacking things together with nix-index just to get a little automagical code generation where users can specify package versions rather than Nixpkgs commits is a kludge. It's cumbersome and rightly turns some developers off from using Nix. Nixpkgs should be enriched or complemented in order to obviate that approach, and the Nix ecosystem will need tooling that has an actual dependency resolver to work with it— even if the only maintained combination of versions for distribution is pretty much singular, and implicitly encoded in Nixpkgs just as it is today.
Other than that, this is being worked on :).
Spack essentially is nix with dependency resolution. spack packages can have conditional (nearly) anything: versions, options, compiler choices, dependencies (including virtual deps). The resolver can make choices about all of those.
See here for more details: https://arxiv.org/abs/2210.08404
Any plans to publish a release version to crates.io, or is it mainly intended as an internal tool for prefix.dev?
I put rust down and maybe I'm stupid but, I was following a 'get started with rust' type of tutorial.
I think I will not look again for some years.
https://github.com/rust-lang/rust/issues/27812
i didn't look any futher.