Make rust versioning make sense (allow building against older rust versions).

[YellowOnion]

according to this: https://github.com/koverstreet/bcachefs-tools/blob/master/rust-src/Cargo.toml#L6

We use version 1.65, but on nixos-stable I get an error:

 error: package `clap_complete v4.4.4` cannot be built because it requires rustc 1.70.0 or newer, while the currently active rustc version is 1.69.0
       > Either upgrade to rustc 1.70.0 or newer, or use

It's probably a good habit to keep an eye on versions, and not expect everyone to be running the latest rust.

@koverstreet @bczhc

[YellowOnion]

Note that: cargo check will validate.

[bczhc]

Thanks for pointing this. I've fixed it in https://github.com/koverstreet/bcachefs-tools/pull/173/commits/bf81a90343a788056f36b976c95f03912f4b777f.

[YellowOnion]

@koverstreet is your custom repo for bindgen still needed? it's not listed on your git anymore, I'm worried it might end up getting garbage collected.

[YellowOnion]

@bczhc okay after banging my head against the wall for a few hours, the only way to validate with 100% certianity, is to use cargo / rust 1.65, cargo update will just add deps that violate the version policy. and I'm still not sure that actually helps.

[bczhc]

Indeed.. Now cargo update doesn't consider MSRVs. I did a quick search and found https://github.com/rust-lang/cargo/issues/9930.

There's a nightly flag minimal-versions can be used: cargo update -Z minimal-versions

[koverstreet]

Yeah, the custom bindgen is still needed.

Doing a proper fix for that is going to require tracking down someone involved with rustc.

[polarathene]

There's a nightly flag minimal-versions can be used: cargo update -Z minimal-versions

You can use the nightly flag -Z msrv-policy and it'll try to resolve compatible semver releases of all deps by the rust-version in your Cargo.toml.

• It relies on the dependency chain each specifying their compatible rust-version as well, otherwise it will assume compatibility.
• Some crates will specify the lowest supported rust version, but it is not with default features so may be a little bit higher (eg: hashbrown presently claims 1.63 but is 1.64 by default unless you pin a dependency (or opt-out of the equivalent default feature).
• Some crates introduce implicit bumps in their own codebase and forget to bump their rust-version (happened recently with tokio-util)

Another alternative is -Z direct-minimal-versions which resolves your direct deps semver as the minimal version. IIRC you can pair that with -Z msrv-policy for implicit deps.

Eventually you'll either need to raise the MSRV of your own crate or to keep it low start pinning implicit deps with cargo update --package <crate> --precise <semver> when necessary (eg: -Z msrv-policy isn't compatible).

---

For CI you can use Cargo.lock.msrv and rename that to Cargo.lock to verify MSRV support.

BTW, rust 1.56 introduces edition 2021, so you might as well bump that:

https://github.com/koverstreet/bcachefs-tools/blob/a613340b26ad88801666362d2824118396f34c38/rust-src/Cargo.toml#L5

Note that your Cargo.toml has patch versions which are probably not the lowest compatible required to install with (-Z direct-minimal-versions), so these could probably be adjusted too:

https://github.com/koverstreet/bcachefs-tools/blob/a613340b26ad88801666362d2824118396f34c38/rust-src/Cargo.toml#L16

Usually that's either the version resolved at the time of adding the dep, or from automated upgrade tools like dependabot bumping unnecessarily.

[YellowOnion]

@polarathene thanks for the advice, I wonder if there's a variant that checks conformity to be included in a test suit so that it can be automated.

@koverstreet I wrote a version that seems to compile on 1.69 it's on my master https://github.com/YellowOnion/bcachefs-tools/commits/master