feat: add sha256 feature to gix-commitgraph

[cruessler]

This PR adds the sha256 feature to gix-commitgraph. I opened it as a draft, so we have a space where we can discuss how to best approach testing this new feature.

This PR was triggered by a comment in #2359.

[Byron]

Thanks a lot, I am looking forward to sorting this out!

There is also #2378, hopefully done in the next couple of days (it might conflict).

[Byron]

Thanks a lot for starting this! This crate is special as it's the first one that parses a file-format that changes depending on the hash kind.

It seems like one commit currently in the gix-object PR would be useful here as well, in case you want to bring it up in its own PR.

[cruessler]

Assuming you’re referring to the one adding Kind::all (6d950f0), I’ll extract that addition into its own PR!

Apart from that, my plan is to go through the tests and, for every tests that currently uses sha1, add a corresponding one that uses sha256. Is that the way to go? Are there other things that would need to be done in this PR?

[Byron]

Assuming you’re referring to the one adding Kind::all (6d950f0), I’ll extract that addition into its own PR!

Yes, that's the one, thanks 🙏.

Apart from that, my plan is to go through the tests and, for every tests that currently uses sha1, add a corresponding one that uses sha256. Is that the way to go? Are there other things that would need to be done in this PR?

Sorry for the confusion, that's the way. The only thing tests have to do is to actively set all hashes using feature toggles, and they should just set sha1/sha256 while they are at it. Once a crate has been converted, the tests should automatically test both hashes, and make sure they are compiled in.

[cruessler]

I added fixtures for SHA256 hashes to gix-testtools and changed gix-commitgraph tests to run for all available hash kinds (those depend on the feature flags passed to gix-commitgraph). This seems to have worked on my machine, but I’m not sure I got the logic in gix-testtools right (any pointers would be much appreciated!). I also added gix-commitgraph to unit-test in justfile, and now I want to see what feedback CI has to give. :-)