Implement support for SPDX-FileContributor

[sgaist]

This patch adds a new parameter that allows to list one or more contributors which will generate the corresponding list of fields in the header.

It refactors SpdxInfo into a dataclass so that it can be used with an optional list of contributors in a simple fashion.

Fixes #615

[carmenbianca]

Hi @sgaist ! Thanks for this PR. It looks awesome. @linozen or me will review this quite soon, because we needed something just like this to implement another feature in #654.

We will also be dropping Python 3.6 support basically now-ish. If Python 3.6 is blocking you, please do ignore it.

[sgaist]

Hi @carmenbianca ! You're welcome. There might be some work to be done on the test side as I only re-implemented two that were obvious good candidate but it might worth refactoring a bit more.

[sisch]

@sgaist For the moment we decided to finish the json PR first and adapt to dataclass in your separate PR. The code locations we needed to change can be found in commit 6b2b3b9ca5fa947a6ced97fa6e7e7fd967f5ccd5. So the best strategy to finish this PR (#669) in my eyes is to merge main after release of PR #654 and add the license_path field to the dataclass.

[sgaist]

@sisch, ok, i'll wait for #654 to be merged and refactor this PR.

One related question: do you prefer that I merge main or rebase my work on it ?

[sisch]

@sgaist I'm afraid I need to pass this question to @linozen: do you know if rebase or merge is preferred?
Personally I think rebase in this specific case is better, but it's not my call, I'm not a maintainer ;)

[mxmehl]

@sisch, ok, i'll wait for #654 to be merged and refactor this PR.

Thank you for your patience!

One related question: do you prefer that I merge main or rebase my work on it ?

In PRs, we usually prefer rebases. In this specific case I personally would also prefer a rebase unless a merge is much easier for you.

[sgaist]

Rebase is perfect, that is my preferred way of working.

I'll keep an eye on #654 to keep things rolling.

[carmenbianca]

I made some small changes and rebased this on top of main. I intend to merge this before #654 because that PR would heavily benefit from the dataclass refactoring.

[nicorikken]

Something to take note of, is that it is not possible to only provide the --contributor parameter:

$ reuse annotate --contributor "A Person" --recusvie myrepo/
 ... (usage info)
reuse annotate: error: option --copyright or --license is required

This can be a design choice, but I can imagine scenario's where a user would like to use a githook to add themselves as contributor, regardless of the copyright or license information. What do you think?

[sgaist]

@nicorikken Good catch ! It's how I thought I had implemented it but did all the tests in the context of making it part of adding either of the other two fields.