If allow-loopback-pinentry is not in gpg-agent.conf, then loopback pinentry mode
is not enabled. In this case, gpg should either issue a warning or an error if
--pinentry-mode=loopback is specified.
How to recreate:
- Make sure ~/.gnupg/gpg-agent.conf does not include allow-loopback-pinentry
- Run echo | gpg2 --pinentry-mode=loopback -s -a
A normal pinentry (i.e., mode=ask) is shown.
A warning or error that loopback mode is not possible.