bug#44090: Packaging a python library that is implemented with rust

[Hamzeh Nasajpour]

Hi,

I'm not expert in rust and python but I need to package a python library, and 
this python library is a wrapper over the rust library. This library is using 
the `setuptools_rust` for build/install. 
* python library: https://github.com/etesync/etebase-py
* rust library: https://github.com/etesync/etebase-rs
* `setup.py`: https://github.com/etesync/etebase-py/blob/master/setup.py

Anyway I need to package this python library. Since guix has two different 
build system for `python` and `rust` I don't know how can I package it. It's a 
python library but it should install some rust library inside the python system 
build.

* This is package definition of `python-setuptools-rust`:
```
(define-public python-setuptools-rust
  (package
    (name "python-setuptools-rust")
    (version "0.11.3")
    (source
      (origin
        (method url-fetch)
        (uri (pypi-uri "setuptools-rust" version))
        (sha256
          (base32
            "1p21sw77197m7pciy8g25bwwaakq1675h0x1lis9sypzr46p2s11"))))
    (build-system python-build-system)
    (native-inputs
     `(("python-setuptools" ,python-setuptools)
       ("python-setuptools-scm" ,python-setuptools-scm)
       ("python-wheel" ,python-wheel)))
    (propagated-inputs
      `(("python-semantic-version"
         ,python-semantic-version)
        ("python-toml" ,python-toml)))
    (home-page
      "https://github.com/PyO3/setuptools-rust";)
    (synopsis "Setuptools rust extension plugin")
    (description "Setuptools rust extension plugin")
    (license license:expat)))
```


* And this is package definition of `python-etebase`. 
```
(define-public python-etebase
  (package
    (name "python-etebase")
    (version "0.30.0")
    (source
      (origin
        (method url-fetch)
        (uri (pypi-uri "etebase" version))
        (sha256
          (base32
            "1py635aqnxx3jy4x6zffriqi0l9gc2gk06h0ms91k4rs68h0gb0i"))))
    (build-system python-build-system)
    (native-inputs
      `(("python-msgpack" ,python-msgpack)
        ("python-setuptools-rust" ,python-setuptools-rust)))
    (inputs
      `(("rust-etebase-rs" ,rust-etebase-rs)))
    (home-page
      "https://github.com/etesync/etebase-py";)
    (synopsis "Python client library for Etebase")
    (description "Python client library for Etebase")
    (license #f)))
```


This is the error in package building:
```
etebase-0.30.0/src/
etebase-0.30.0/src/lib.rs
etebase-0.30.0/src/glue.rs.in
phase `unpack' succeeded after 0.0 seconds
starting phase `ensure-no-mtimes-pre-1980'                                      
                                                                                
                                              
phase `ensure-no-mtimes-pre-1980' succeeded after 0.0 seconds
starting phase `enable-bytecode-determinism'                                    
                                                                                
                                              
phase `enable-bytecode-determinism' succeeded after 0.0 seconds
starting phase `patch-usr-bin-file'                                             
                                                                                
                                              
phase `patch-usr-bin-file' succeeded after 0.0 seconds
starting phase `patch-source-shebangs'                                          
                                                                                
                                              
phase `patch-source-shebangs' succeeded after 0.0 seconds
starting phase `patch-generated-file-shebangs'                                  
                                                                                
                                              
phase `patch-generated-file-shebangs' succeeded after 0.0 seconds
starting phase `build'                                                          
                                                                                
                                              
running "python setup.py" with command "build" and parameters ()
running build
running build_py
creating build
creating build/lib
creating build/lib/etebase
copying etebase/__init__.py -> build/lib/etebase
running build_ext
running build_rust
error: Can not find Rust compiler
command "python" "-c" "import setuptools, 
tokenize;__file__='setup.py';f=getattr(tokenize, 'open', 
open)(__file__);code=f.read().replace('\\r\\n', 
'\\n');f.close();exec(compile(code, __file__, 'exec'))" "build" failed with 
status 1
builder for 
`/gnu/store/45b049cf1k8czxmvwqi3yw6gyk5s7hx5-python-etebase-0.30.0.drv' failed 
with exit code 1
build of /gnu/store/45b049cf1k8czxmvwqi3yw6gyk5s7hx5-python-etebase-0.30.0.drv 
failed
View build log at 
'/var/log/guix/drvs/45/b049cf1k8czxmvwqi3yw6gyk5s7hx5-python-etebase-0.30.0.drv.bz2'.
guix build: error: build of 
`/gnu/store/45b049cf1k8czxmvwqi3yw6gyk5s7hx5-python-etebase-0.30.0.drv' failed

```



Sorry for duplication, I sent this email here too: 
https://lists.gnu.org/archive/html/help-guix/2020-10/msg00092.html
then I thought this mailing list is better for asking this type questions.



Regards,
Hamzeh