Fill in `DEPEND=">=virtual/rust-x.y.x"` using `rust-version` from `Cargo.toml`

[vincentdephily]

This is just a paper cut, but I imagine the fix is easy enough.

[gyakovlev]

it's BDEPEND
also note that eclass specifies it's minimal rust version due to reliance on cargo features in particular release.
as even if upstream specifies minimum 1.57.0, if eclass uses 1.65.0 features - we should never go below eclass constraint.
https://github.com/gentoo/gentoo/blob/master/eclass/cargo.eclass#L37
this is current version
it will be bumped to 1.59.0

[gyakovlev]

https://github.com/gyakovlev/gentoo/blob/cad363d50fcbe1f7f84d78660d61a196e61d9b93/eclass/cargo.eclass#L33
this is new eclass version that will land soon

[gyakovlev]

so if it somehow could read eclass's RUST_DEPEND and only set minimum version only if it's above RUST_DEPEND

[vincentdephily]

Good catch re BDEPEND.

We could probably just concatenate the crate and eclass MSRV together, and let portage sort out the resulting minimum.

On that note, when does the eclass evaluate BDEPEND="${RUST_DEPEND}" ? Shouldn't it evaluate BDEPEND="${BDEPEND} ${RUST_DEPEND}" to avoid overwrites ?