[WIP] Support GPG-signing commits

[tommyip]

This is a work in progress, just wanted to publish it early to gather some feedback.

TODO:

• git record (calls git commit directly so signing already works in master, added new flags to override keyid or disable signing)
• git amend
• git move
  • in-memory
  • on-disk
• git sync
• git restack
• git reword
• git test
  git branchless snapshot create

Also looking in ways to write integration tests for this. Generating keys through gpg and using them in tests seems a bit cumbersome.

Fixes #465

[arxanas]

Thanks for looking into it!

git branchless snapshot create

We shouldn't need/want to sign snapshot commits (although you can if it's easier). These are just meant to store the working copy state to either attach to a real commit later (which would be signed at that time) or to restore the working copy state (which doesn't need to be signed).

Also looking in ways to write integration tests for this. Generating keys through gpg and using them in tests seems a bit cumbersome.

Would you be able to generate a single key ahead of time and commit it to the repo? Although I don't know if that would remove the dependency on gpg at test-time.

[arxanas]

Most likely you can ignore the warning about

using a potentially dangerous silent `as` conversion

here. That's meant for numeric types (like u32 <-> u64), but it looks like git2_ext::ops::Sign is not a numeric type, so I don't know why the warning is triggereing here.