Basic Packagedcode module for handling Rust's cargo crates

[ritiek]

A very basic implementation at the moment. This is still missing tests which I'll add in shortly.

Otherwise, this is ready for review!

[ritiek]

Also see #1424.

[ritiek]

For those looking to quickly test this out. Clone any Rust repository and run scancode on it:

$ git clone https://github.com/jvns/snake.rs
$ scancode --package snake.rs/ --json-pp -

[codecov]

Codecov Report

Merging #1426 into develop will decrease coverage by 0.02%.
The diff coverage is 60.78%.

@@             Coverage Diff             @@
##           develop    #1426      +/-   ##
===========================================
- Coverage    83.84%   83.81%   -0.03%     
===========================================
  Files          119      120       +1     
  Lines        14041    14091      +50     
===========================================
+ Hits         11772    11810      +38     
- Misses        2269     2281      +12

Impacted Files	Coverage Δ
src/packagedcode/npm.py	84.83% <0%> (ø)	⬆️
src/packagedcode/__init__.py	75.86% <100%> (+0.86%)	⬆️
src/packagedcode/cargo.py	61.22% <61.22%> (ø)
src/commoncode/fileutils.py	82.5% <0%> (+1.32%)	⬆️
src/scancode/extract_cli.py	88% <0%> (+3%)	⬆️

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[pombredanne]

Thank you ++ this is looking very good!
🙇‍♂️

[ritiek]

I've added some tests as well.

This should be ready to merge if everything looks good. I think we could extend the subclass for handling more Cargo.toml attributes in an another PR. As it would be a big task in itself.

[pombredanne]

This all looking good.
Thanks ++
Merging now.

[pombredanne]

That's not your making but this is a weird test that I will need to fix.