rust and rust-bin out of sync?

[Greg Troxel <gdt%lexort.com@localhost>]

We're heading to pre-freeze so I am wondering what is the plan for rust
for 2023Q3.

lang/rust	is at 1.70.0
lang/rust-bin   is at 1.69.0

wip/rust	is at 1.71.1

devel/cargo-c	is at 0.9.23


I have a box which is netbsd-10 amd64, just before the openssl pullup,
with rust-bin installed, and cargo-c is failing to build:

  ===> Building for cargo-c-0.9.23
     Compiling cargo v0.72.2
  error[E0658]: use of unstable library feature 'once_cell'
     --> /tank0/ztmp/work/devel/cargo-c/work/vendor/cargo-0.72.2/src/cargo/util/mod.rs:215:9
      |
  215 |     use std::sync::OnceLock;
      |         ^^^^^^^^^^^^^^^^^^^
      |
      = note: see issue #74465 <https://github.com/rust-lang/rust/issues/74465> for more information

It seems an obvious upstream bug in cargo to use an "unstable library
feature" rather than a year-numbered edition, but this is rust :-(

It seems obvious that anything rust in tree needs to build with rust and
rust-bin both, and that updates to new code shouldn't happen if that
isn't true.  This is especially important for any computers without
gigabytes of extra RAM.  I can certainly see this going unnnoticed very
easily, so this isn't a complaint that it happened (if that is indeed
what happened), just pointing out that we need a get-well plan.

Questions arising:

  Am I confused about that I'm seeing, or is it just me?

  What's up with cargo-c?  It is not declared as needing any particular
  version of rust (and it seems quite unreasonable to need anything
  bleeding edge, so saying it needs 1.70 doesn't really seem ok if
  rust-bin is at 1.69).  1.69 is really not that old.  Is this release
  just broken?  Something else?  (I have a build of the previous version
  in process.)

  Is there a reason rust-bin is behind rust?  Just round tuits?  Is
  someone going to move rust-bin to 1.70.0 before 9/1?

  Is anyone thinking of landing 1.71.1 in lang/rust before 9/1?  I would
  guess not because I haven't been hearing about a call for testing
  already -- but I could be off.