Support commit signing with gpgme

[dnaka91]

Support for creating signed commits with the help of gpgme as discussed in #97.

Currently still WIP, especially many potential corner cases due to manually implementing amend
as the git2 crate doesn't provide a function to amend + re-sign commits easily.

[dnaka91]

Currently builds fail due to the missing gpgme library. made a few adjustments so it should work now on Linux and MacOS, but it's likely to still fail on Windows. I guess we'll have to set env vars accordingly.

Also, what would be the preferred way of linking? I guess only dynamic linking is an option, as static linking against GPLed libs would require to change the license of this project too.

If we link dynamically, the build process becomes more complicated, and distribution as well. We have to ask users to install the gpgme libraries.

• On Linux that's just a apt-get install gpgme (or similar for other package managers.
• On MacOS it's a simple brew install gpgme.
• On Windows that would be either choco install gpg4win or manual installation. Problem here is that the installation target dir can be customized and gitui may not find them every time.

[Kqzz]

would this fix this issue?

[mainrs]

As I already mentioned in sdttttt/gcr#53, gpgme is imo not a good choice for a cross-platform binary. It it inevitabely hard to get to compile on Windows and even if one manages to compile it, it only works in 32bit mode.
And I think that dynamic linking should be a no-go. It requires users to download the binary from their distribution. And on Windows it might not even work 100% of the time since the installation path can be changed by the user.

I think the only viable solution would be to either bite the bullet and actually try to make gpgme work for 32bit Windows on CI. Or to move on to sequoia_openpgp and try to that library.

[dnaka91]

I actually never really started using gitui that much so I don't really find the motivation to complete this.

Compilation on windows doesn't really seem solvable neither so it's better to go another course. As mentioned sequoia-gpg might be one solution or maybe just doing the same as git and shell out to gpg.

Therefore I'm closing this in favor of another way of adding gpg support.