Stable GnuPG interface, git should use GPGME

Dear Git-Devs,

git uses an pipe-and-exec approach to running a GnuPG binary as writen in the documentation [1]:

    gpg.program
           Use this custom program instead of "gpg" found on $PATH when making
           or verifying a PGP signature. The program must support the same
           command-line interface as GPG

please consider using libgpgme interfacing to GnuPG, because the gpg command-line interface is not considered an official API to GnuPG by the GnuPG-devs and thus potentially unstable.

== Details

I'm involved in GnuPG development. For most applications using libgpgme is the way what GnuPG-devs would recommend, also see

  https://wiki.gnupg.org/APIs .

GnuPG devs are making a good effort of trying to keep the command-line interface stable, though it is not for sure. Git is only using a small part of the interface, so the risk when keeping the current way is small. Still I believe git's stability and usability would profit when moving to libgpgme, especially with the coming move to GnuPG 2.2, better diagnosing messages and for cross-plattform usage.

== Usability problem with `gpg2` vs `gpg`

My use case today was signing and git by default found the `gpg` binary by default and the command failed. The reason is that I have `gpg2` installed and most applications use it right away. So git failed signing because the .gnupg configuration of the user was not ready for the old `gpg` which is still installed on Debian GNU/Linux for purposes of the operating system. If git would have used libgpgme, gpgme would have choosen the most uptodate version of `gpg` available (or configured) without me intervening via gpg.program. Now because of this problem you could adding a check for `gpg2` and fallback to `gpg`, but even better would be to move to libgpgme. >:)

Best Regards and thanks for maintaining Git as Free Software, Bernhard

== how to respond

ps: Please copy me on replies as I am not on git@vger.kernel.org. pps: I've copied gnupg-devel@ so they can see I've send this report, you don't have to.

[1] https://github.com/git/git/blob/3bc53220cb2dcf709f7a027a3f526befd021d858/Documentation/config.txt search for 'gpg.program'.