Support GPG-signing commits

[arxanas]

Some resources:

• Using git2's Repository::commit_signed: How to correctly create GPG-signed commits? rust-lang/git2-rs#507. It looks like you still need to sign the commit via GPG yourself.
  • Another example of signing the commit: https://blog.hackeriet.no/signing-git-commits-in-rust/
• An implementation for git-revise: Add support for GPG-signed commits (#46) mystor/git-revise#73

There's a few APIs in git-branchless which are capable of creating commits:

• Repo::create_commit.
• Repo::cherry_pick_commit and Repo::cherry_pick_fast.
• Repo::amend_fast.

These commands are capable of creating commits:

• git move.
  • Note that it can create commits in-memory or on-disk via git rebase, so both cases will have to be handled.
  • The calling code is in core::rewrite::execute. We'll probably want to add some configuration to to indicate that any commits created in this way should be signed. Also CherryPickFastOptions.
• git amend.
• git reword.
• git sync and git restack: these should be handled fairly straightforwardly by whatever changes are made to support git move.
• git record: experimental command, so not a priority at the moment.
• git branchless snapshot create: these commits don't need to be signed since they're not supposed to be really committed/pushed.

These data structures will probably have to be updated to carry GPG information. You should be able to add a field and then follow the compiler errors to see where should be updated to use the new field:

• AmendFastOptions.
• CherryPickFastOptions
• ExecuteRebasePlanOptions
• MoveOptions
• There is no explicit data structure for Repo::create_commit options, but it would be reasonable to add one.

In the long term, it would be best to contribute GPG-signing code to https://github.com/gitext-rs/git2-ext in some capacity. Either we can contribute it directly there, or contribute it to git-branchless first and extract it afterwards.

[lthms]

Awesome, @arxanas. Thanks a lot for this carefully written issue.

This is probably more challenging than what I had anticipated, though I am not surprise. I will take the time to review the various links you have gathered here, and give it a try at some point.

[epage]

FYI I just released git2-ext v0.2 which has some of the basics of signing support implemented

• A Sign trait
• A commit that takes Sign
• Updated reword and amend to take Sign

The only thing I didn't touch is the cherry_pick implementation as that uses git2's rebase mechanism and I don't see a way do to sign those.

[epage]

Also, for full git compatibility, we should try to support what is documented at https://github.com/git/git/blob/4f6db706e6ad145a9bf6b26a1ca0970bed27bb72/Documentation/config/gpg.txt

[epage]

I've done another release of git2-ext that re-implements git's gpg, x509, and ssh signing behavior.

The one problem with it is when the key is in a file, we do not yet correctly handle ~/. Knew that is complex enough that I didn't want to implement it myself and didn't find a crate to do it for me that was cross-platform.

[hauleth]

Yeah, I have just noticed that my signed commits are missing and just found that issue. It is not super urgent for me, but I wanted to know if there is timeline for this feature?

[arxanas]

@hauleth there are no plans to work on this. You might want to try jj instead, which has a draft PR; see the issue at jj-vcs/jj#58

[hauleth]

@arxanas I got used to git-branchless and I do not know if I want to test another implementation. If anything I would probably look how to implement it there. I was just curious if anyone is working on that yet. It is minor issue, but I just wondered if there are any plans for adding support for signing.