gpgme 1.9.0_1: Bad dependency on gnupg21

[jdswinbank (John Swinbank)]

As of #51650, gnupg21 provides ${prefix}/bin/gpg (not gpg2). This breaks the gpgme dependency on path:bin/gpg2:gnupg2.

[lbschenkel (Leonardo Brondani Schenkel)]

@dbevans: it seems that the current gpg situation became a little bit messy:

• gnupg installs on bin/gpg
• gnupg2 installs on bin/gpg2
• gnupg21 installs on bin/gpg and conflicts with both gnupg and gnupg2

I think that it's probably worth it to open a discussion on the mailing list about how to handle the various GnuPG versions moving forward -- including 2.2 that was just released.

Regarding GPGME, for now I suggest that we introduce a gnupg20 variant which is activated by default and has the current dependency, so no change for existing users. Users using 2.1.x need to select the gnupg21 variant instead that will have a hard dependency on gnupg21 (we cannot rely on path:bin/gpg anymore since it could be satisfied by GnuPG 1.x), giving them an immediate solution. Then we can decide later when it is appropriate to switch defaults. How does that sound?

[lbschenkel (Leonardo Brondani Schenkel)]

I have submitted a tentative fix implementing my proposal above on ​https://github.com/macports/macports-ports/pull/743 for review/discussion.

[lbschenkel (Leonardo Brondani Schenkel)]

In ce3044a66aedbe344e92d20136c1d71175f94bb1/macports-ports:

gpgme: Add +gnupg20 and +gnupg21 variants

GnuPG 2.1.x (port gnupg21) now installs as ${prefix}/bin/gpg instead of
${prefix}/bin/gpg2, which makes it conflict with this port due to the
dependency on path:bin/gnupg2 -- this forces the installation of gnupg2
but that is not satisfiable (gnupg2 conflicts with gnupg21).

This commit addresses this issue by adding two variants, gnupg20 and
gnupg21, which allow the specific version that this port will depend on.
If none is explicitly chosen, gnupg20 is selected to preserve the old
behaviour.

Closes: #54749