Re: [PATCH v5 0/9] Introduce Rust and announce that it will become mandatory

[Sam James <sam@gentoo.org>]

Patrick Steinhardt <ps@pks.im> writes:

> On Mon, Sep 15, 2025 at 08:03:29PM -0600, Ezekiel Newren wrote:
>> I am currently working on a patch series that makes Rust optional and
>> addresses several concerns that this series does not:
>>   * Rust calling C: Makefile has no way to build or run Rust so it
>> would have to call cargo test, but that doesn't work unless build.rs
>> tells cargo where libgit.a is (among other things).
>>   * Build tooling alignment: My build_rust.sh is called by make and
>> meson which eliminates defining how to build Rust in 2 places.
>>   * Cargo vs Meson: Meson is adding support for Rust and it's getting
>> better, but Cargo is the canonical build system for Rust. cargo is
>> released in lockstep with rustc, and we _have_ to use cargo when
>> building with make because Meson won't be available in that case.
>>   * Crates: Patrick's series assumes the Git codebase is _the_ crate
>>     * cbindgen: Cbindgen outputs a single header file for each crate,
>> with only 1 we'll have an unmanageably large auto generated header
>> file.
>>     * Modularity: Using multiple crates makes Git more modular. Elijah
>> told me that there was some desire to make Git more modular.
>>     * Cargo Dependencies: Patrick wrote his series with Meson first in
>> mind which doesn't address how we'll be able to use crates from
>> crates.io
>>   * CI:
>>     * Sparse coverage: I think there's only one target that tests his changes.
>>     * With vs Without Rust: I don't see anywhere that he covers
>> building with vs without Rust in CI
>>   * Build integration: Meson has to have every .rs file specified
>> where as the default layout of a Rust project allows Cargo to just
>> know where to look for .rs files
>
> Yeah, as I mentioned my patch series here really aims at getting an
> minimum viable user of Rust into the Git codebase so that we can focus
> the discussion more on the roadmap towards Rust rather than the actual
> Rust infrastructure. The whole infra is very simplistic because of that,
> but that is intentional for now.
>
> Once we have agreed on the roadmap I very much expect that we will
> iterate on it to allow for more complex use cases. My next step would
> have been to pick patches from your series that make all of this work
> on Windows. But of course I don't have to be the (only) one to iterate
> on the initial simple infrasturcture, this should ideally be an effort
> by the whole community.
>
> And yes, many of the points you mention above are things we'll have to
> address over time to make Rust a viable alternative to implement
> anything more complex than the trivial "varint.c" thing. I think that
> iteration is key here: let's start simple and then gradually build out
> the infrastructure.

I think adding external crates especially will need discussion given the
licencing and "offline" issues (which are solvable but they should be
examined).

>
> Patrick