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Comment by oconnor663 | Hacker News Reader

I think it would be pretty natural for a distro to run it's own crates.io/PyPI/NPM mirror to build packages against, and have a unified set of library versions for the entire OS that way. Maybe not even a server, maybe just a giant Git repo or whatever, filtered down to the set of packages they actually use. Have any of them tried this?

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Debian effectively does this. It doesn't actually implement the crates.io API, but when building a Rust package they tell cargo "look in this directory for dependencies, don't talk to the network".

As I understand it, the process goes something like this:

- Debian wants to package a Rust tool

- They examine the tool's Cargo.toml file to determine its immediate dependencies

- Those Rust dependencies are converted into Debian package names

- Generate a Debian package definition that lists those dependencies under "Build-Depends"

- When building the Debian package in an isolated environment, Build-Depends packages are installed, providing things like `rustc` and `cargo` as well as putting the dependencies' source into the "local dependencies" directory

- Cargo runs, configured to only look in the "local dependencies" directory for dependencies

- the resulting binary is scooped up and packaged

Is there some documentation on how to do this yourself? It sounds very useful for building software meant to be binary distributed.

The whole process seems to be compiled in this Readme: https://salsa.debian.org/rust-team/debcargo-conf/blob/master... How to use only local packages can be found in the last paragraph.

Is this documented anywhere?

See https://wiki.debian.org/Teams/RustPackaging/Policy

Is this automated? Does doing this manually do anything for Debian other than create a headache and a mountain of work?

If it were up to me, I’d consider carving off part of the Debian package namespace - like cargo—* for cargo packages, and just auto-create them (recursively) based on the package name in cargo. There are a few things to figure out - like security, and manually patched packages, and integrating with cargo itself. But it seems like it should be possible to make something like this work with minimal human intervention.

Yes, it's heavily automated.

Why not just vendor the source for each Rust tool separately? A lot simpler and more reliable.

The only downside I can see is disk space usage on the builder machines, but it's source code... is it really that big?

Generally distributions want to unify dependencies so that if there’s a security fix, they only need to do it once instead of for every program.

> Debian effectively does this. It doesn't actually implement the crates.io API, but when building a Rust package they tell cargo "look in this directory for dependencies, don't talk to the network".

That sounds close to what I had in mind, but I assume you run into problems with the finer points of Rust's dependency model. Like if I depend on libfoo v1, and you depend on libfoo v2, there are a lot of situations (not all) where Cargo will happily link in both versions of libfoo, and applications that depend on both of us will Just Work. But if libfoo needs to be its own Debian package, does that mean every major version is a different package?

That's the first question that comes to mind, but I'm sure there are others like it. (Optional features? Build vs test dependencies?) In short, dependency models (like Cargo's and Debian/APT's) are actually pretty complicated, and ideally you want to find a way to avoid forcing one to represent all the features of the other. Not that I have any great ideas though :p

Haskell has Stackage[1] which maintains globally consistent sets of Haskell packages that build together. It’s of course a huge pain to maintain, probably exponentially harder wrt <size of package registry> / <size of Hackage>. Also highly depends on whether the language and ecosystem helps and encourages library authors to maintain compatibility; I don’t think Rust does.

[1] https://www.stackage.org/

I’m not aware of any that have; this would require them to become experts in running parallel infra, in many languages and with varied setups, and would mean that they’re not longer self-contained. That feels antithetical to their goals to me at least.

I mean Ubuntu has a bunch of python libs. The problem is that you need to make a universe of mutually compatible libs, so if _any_ of the libs have old-ish dependencies, that holds back so much.

I think what happens in practice is package maintainers do the work to get things up to date, and so only include a subset.

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