Allow packaging specifiers in packages when auditing on PyPI

[nicholasjng]

Packaging specifiers are implemented as described in https://packaging.python.org/en/latest/specifications/version-specifiers/, although I did not find a specific PEP for them. Everything is done using packaging's own APIs, so there are no egregious hacks brought into the spec parsing logic.

This allows to audit version-specific packages, which makes it easier to pin down regressions in ABI3 compatibility.

Usage: abi3audit cryptography==42.0.7 -v.

Currently lacks support for version ranges, but that is only a regex tweak away thanks to the terrific SpecifierSet API.

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Hello again, I'm on a roll! I was surprised to see that version-specific auditing of a PyPI package was not supported, so I quickly added it. On this branch (please try it out as well), I get:

$ abi3audit -v cryptography==42.0.7
[17:49:56] 💁 cryptography==42.0.7: 23 extensions scanned; 0 ABI version mismatches and 0 ABI violations found

$ abi3audit -v cryptography==lolwat      
[17:50:21] 👎 processing error: 'cryptography==lolwat' does not look like a valid wheel, shared object, or package name 

The error message in the second one could be improved, since packaging throws a good error on a wrong specifier. But that would probably require meddling with the spec parsing routine as a whole, which I skipped for now.

[woodruffw]

Thanks @nicholasjng! This has been on my wishlist for a while 🙂

Everything is done using packaging's own APIs, so there are no egregious hacks brought into the spec parsing logic.

Much appreciated!

[woodruffw]

Thanks @nicholasjng, this is great!

[nicholasjng]

My pleasure. I'll throw you the followup (dep ranges) over the fence either today or tomorrow.