Re: [PATCH 3/3] rust: generate bindings via cbindgen

[Patrick Steinhardt <ps@pks.im>]

On Mon, Oct 27, 2025 at 09:15:51PM -0700, Junio C Hamano wrote:
> "brian m. carlson" <sandals@crustytoothpaste.net> writes:
> 
> > On 2025-10-27 at 20:35:59, Ezekiel Newren wrote:
> >> On Fri, Oct 24, 2025 at 12:37 AM Patrick Steinhardt <ps@pks.im> wrote:
> >> > > cbindgen is a Rust crate and it should be specified in the Cargo.toml
> >> > > under [build-dependencies] block.
> >> >
> >> > What is the benefit for us? The generated code is not a dependency of
> >> > the Rust code, and neither do we use it via "build.rs". And if we use
> >> > cbindgen via "Cargo.toml" we'd be forced to build it first, which slows
> >> > down our CI jobs.
> >> >
> >> > Please let me know in case I miss any reasons to have it in our build
> >> > dependencies instead.
> >> 
> >> You're targeting a very old version of Rust (1.49). I'm not even sure
> >> that cbindgen will work with a version that old, but if it does then
> >> we should use it in build.rs to make sure we're not using any features
> >> of cbindgen that aren't available until later versions.
> > ...
> > For instance, I'm using Debian unstable with a system cbindgen 0.27.0.
> > This requires Rust 1.70 or newer. If I use rustup to test my code on
> > Rust 1.49, then the code won't compile for me.
> 
> Have we even agreed on which Rust version we would aim for?  With
> BreakingChanges.adoc We have agreed to make some version of Rust
> mandatory by the time we hit Git 3.0 but IIRC, there isn't anything
> written down except for an old message from you
> 
>   https://lore.kernel.org/git/ZZ9K1CVBKdij4tG0@tapette.crustytoothpaste.net/
> 
> that expressed your preference to support the version of Rust in the
> latest Debian stable plus the version in Debian's oldstable until
> the latest stable has been out for a year, which nobody responded
> to, so we cannot quite say that is the consensus of the community,
> yet.

For now that Rust version is 1.49, and that's enforced by our CI. The
reason for this specific version is that it's the target version for the
gcc-rs folks, so it may help currently-unsupported platforms to get
support earlier.

But I made clear in past patch series that if we have strong reasons to
use a more recent version of Rust, then we should update. I mostly
wanted us to do this intentionally than picking any random Rust version
and saying that "this is it now".

Patrick