Some supplemental information:
This is happening on every email delivered into Dovecot
via LMTP. The curious things are that the message is a)
successfully delivered and b) sieved into the correct directory.
Another observation is that:
mail_deliver_ctx_get_log_var_expand_table
is defined globally in core/src/lib-lda/mail-deliver.c (and used
there) but the ONLY external call in the entire dovecot tree is
from pigeonhole/src/plugins/lda-sieve/lda-sieve-log.c.
I am not using lda but it seems to be part of core. So, as I am
only using lmtp, why is pigeonhole using lda-sieve at all?
It's part of lib-lda, which is also used by lmtp.
Can I work around the error message by some config magic (as I did
by calling the correct plugin for imap_sieve) or is this an actual
bug? Could this be fixed simply by including mail-deliver.h in
lda-sieve-log.c?
I think you're not linking lmtp binary correctly somehow. That symbol should be part of it:
% nm /usr/libexec/dovecot/lmtp | grep mail_deliver_ctx_get_log_var_expand_table
0000000000061960 T mail_deliver_ctx_get_log_var_expand_table