This allows 'match-record' to be more efficient (field offsets are
computed at compilation time) and to report unknown fields at
macro-expansion time.

* guix/records.scm (map-fields): New macro.
(define-record-type*)[rtd-identifier]: New procedure.
Define TYPE as a macro and use a separate identifier for the RTD.
(lookup-field, match-record-inner): New macros.
(match-record): Rewrite in terms of 'match-error-inner'.
* tests/records.scm ("match-record, simple")
("match-record, unknown field"): New tests.
* gnu/services/cuirass.scm (cuirass-shepherd-service): Rename 'log-file'
local variable to 'main-log-file'.
* gnu/services/getmail.scm (serialize-getmail-configuration-file): Move
after <getmail-configuration-file> definition.

Fixes a regression introduced in
44554e7133aa60e1b453436be1e80394189cabd9 whereby the wrong record fields
would be accessed, leading to a <location> record being spliced in the
result.

* gnu/services/getmail.scm (serialize-getmail-configuration-file): Use
'match-record' instead of 'match'.
(getmail-shepherd-services): Likewise.

* gnu/home/services/ssh.scm (serialize-address-family): Use the public API of
the maybe infrastructure.
* gnu/services/file-sharing.scm (serialize-maybe-string): Use maybe-value.
(serialize-maybe-file-object): Use maybe-value-set?.
* gnu/services/getmail.scm (getmail-retriever-configuration): Don't use
internals in unset field declarations.
(getmail-destination-configuration): Ditto.
* gnu/services/messaging.scm (raw-content?): Use maybe-value-set?.
(prosody-configuration): Use %unset-value.
* gnu/services/telephony.scm (jami-shepherd-services): Use maybe-value-set?.
(archive-name->username): Use maybe-value-set?.
* tests/services/configuration.scm ("maybe type, no default"): Use
%unset-value.

Modified-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>

* gnu/services/authentication.scm (fprintd-configuration)
(nslcd-configuration): Substitute file-like objects for package ones.
* gnu/services/cgit.scm (cgit-configuration, opaque-cgit-configuration):
Likewise.
* gnu/services/cups.scm (package-list?, cups-configuration): Likewise.
* gnu/services/dns.scm (verify-knot-configuration)
(ddclient-configuration): Likewise.
* gnu/services/docker.scm (docker-configuration): Likewise.
* gnu/services/file-sharing.scm (transmission-daemon-configuration): Likewise.
* gnu/services/getmail.scm (getmail-configuration): Likewise.
* gnu/services/mail.scm (dovecot-configuration)
(opaque-dovecot-configuration): Likewise.
* gnu/services/messaging.scm (prosody-configuration)
(opaque-prosody-configuration): Likewise.
* gnu/services/monitoring.scm (zabbix-server-configuration)
(zabbix-agent-configuration): Likewise.
* gnu/services/networking.scm (opendht-configuration): Likewise.
* gnu/services/pm.scm (tlp-configuration): Likewise.
* gnu/services/telephony.scm (jami-configuration): Likewise.
* gnu/services/virtualization.scm (libvirt-configuration)
(qemu-guest-agent-configuration): Likewise.
* gnu/services/vpn.scm (openvpn-client-configuration): Likewise.

* gnu/services/getmail (getmail-retriever-configuration): Fix typo.

Change the message-log-syslog and message-log-verbose configuration values to
match the Getmail defaults.

* gnu/services/getmail.scm (getmail-options-configuration): Change defaults
for message-log-syslog and message-log-verbose
* doc/guix.texi (Mail Services): Update the Getmail documentation accordingly.

* gnu/services/getmail.scm (getmail-retriever-configuration): Specify proper
documentation strings for some of the fields.
* doc/guix.texi (Mail Services): Update the documentation accordingly.

* gnu/services/getmail.scm (getmail-shepherd-services): Add a stop component
to the shepherd services.

* doc/guix.texi (Getmail service): Remove the word `not'.
* gnu/services/getmail.scm (getmail-options-configuration): Ditto.

Getmail is a mail retriever written in Python, this commit adds a service-type
to run getmail. I'm looking at this, as it's a convinient way of getting
mailing list messages in to Patchwork.

I initially tried putting this in the (gnu services mail) module, but due to
also trying to use the define-configuration pattern, it conflicted with the
dovecot service.

* gnu/services/getmail.scm: New file.
* gnu/local.mk: Add it.
* gnu/tests/mail.scm (%getmail-os, %test-getmail): New variables.
(run-getmail-test): New procedure.