[Libguestfs] Cargo edition problem with Debian 11

[alan somers]

I think we should downgrade predicates-tree to 1.0.5 or older.  I can
submit a PR for that.  What does "rustc --version" show you?

On Fri, Jan 13, 2023 at 2:41 AM Richard W.M. Jones <rjones at redhat.com> wrote:
>
>
> https://gitlab.com/nbdkit/nbdkit/-/jobs/3598390121
>
> ----------------------------------------------------------------------
> cargo build --release --example ramdisk
>  Downloading crates ...
>   Downloaded float-cmp v0.9.0
>   Downloaded downcast v0.11.0
>   Downloaded mockall_derive v0.11.3
>   Downloaded itertools v0.10.5
>   Downloaded aho-corasick v0.7.20
>   Downloaded predicates-tree v1.0.7
> error: failed to parse manifest at `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/predicates-tree-1.0.7/Cargo.toml`
> Caused by:
>   failed to parse the `edition` key
> Caused by:
>   this version of Cargo is older than the `2021` edition, and only supports `2015` and `2018` editions.
> ----------------------------------------------------------------------
>
> nbdkit itself uses edition = 2018, but this seems to affects one of
> the dependencies.
>
> I'm not sure how to solve this, but one ideas I had is in ./configure
> to check if the cargo/rust we're trying to use doesn't support some
> base edition (eg. latest edition supported < 2021) then we would
> disable rust bindings.
>
> Unfortunately actually getting the latest supported edition seems
> hard.  The best I could find is parsing this which doesn't seem ideal:
>
> $ rustc --help |& grep -- --edition
>         --edition 2015|2018|2021|2024
>
> What do you think?
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> libguestfs lets you edit virtual machines.  Supports shell scripting,
> bindings from many languages.  http://libguestfs.org
>