[Rust] Re: Can we get rid of some Python dependencies in all Rust builds

[Fabio Valentini]

On Mon, Jul 11, 2022 at 6:48 PM Miro Hrončok <mhroncok(a)redhat.com&gt; wrote:
>  Hello Rust folks,
>
>  I see that all Rust crate packages require rust-packaging which in turn
>  requires python3-rust2rpm. That brings in:
>
>    - Python (obviously)
>    - python-jinja2
>    - python-requests
>    - python-tqdm
>
>  I always forget about this when I try to do some impact checks in Copr.
>  Currently, I am rebuilding all (transitive) build-dependents of
>  python-markupsafe in Fedora 35 and 36 due to a requested update. This includes
>  ~2k rust packages that could probably be skipped, becasue markupsafe is
>  required by jinja2.
>
>  Do all rust packages indeed need all 3 listed Python libs on runtime?
>
>  As far as I understand, Python is used in the dependency generators trough the
>  cargo-inspector entry-point. So, let's live with that. jinja2, requests and
>  tqdm all seem to only by imported from the rust2rpm entrypoint (rust2rpm.__main__).
>
>  Can we please get rid of this dependency? It could be done on several levels:
>
>    1) upstream pyp2rpm, either or:
>      a) split the project into inspector, rust2rpm and common
>         -- I consider this tedious
>      b) make rust2rpm CLI a Python extra
>         -- I consider this bad UX, since the upstream project *is rust2rpm*
>
>    2) downstream rust-pacakging, all of the following:
>      - move crate-inspector bits to rust-pacakging
>      - stop requiring python3-rust2rpm from rust-pacakging
>      - use modern Python macros to install the entry_point via pip
>        (this is needed to be able to run ti without the metadata installed)
>
>  I have a proof of concept for (2) but it requires some small adjustment
>  upstream -- the inspector module must not import form __main__ (that is very
>  bad habit): https://src.fedoraproject.org/rpms/rust-packaging/pull-request/3
>
>  WDYT? 
My PR to split core functionality from the things that need
third-party python packages has been merged:
https://pagure.io/fedora-rust/rust2rpm/pull-request/204

Once this is released as part of rust2rpm v22, we can adapt the
packaging so that cargo-inspector will no longer pull in any
third-party python packages, as it now only needs the python3
interpreter and only imports things from the python standard library.

I don't think we can get rid of the python3 interpreter dependency,
unless we rewrite the RPM dependency generator bits (cargo-inspector)
in some other language.
But other than that, does this improve the situation from your POV?

Fabio