From 82264461e530e55af670c1d92a38eb8a63b5f4fb Mon Sep 17 00:00:00 2001
From: Karl Hallsby <karl@hallsby.com>
Date: Sat, 27 Jun 2020 15:26:11 +0200
Subject: [PATCH] mbsync: only generate group/channel configuration if channels
 present

Typically, when a group is specified, channels will be specified as
well. However, if due to error or mistake, the user forgets to specify
ANY channels for a group, we should not generate that group's
information.

This means that no channels are specified (which maps the remote
master to local slave). In addition, the `Group <gName>` block (which
brings the separate channels together) is also not generated.

Another thing to consider is that a user might specify a group and a
channel, but perform no additional configuration of the channel.
In a configuration, this would be realized by
`accounts.email.accounts.<aName>.mbsync.groups.<gName>.channels.<cName>;`

This creates the channel with the name `<cName>` and the
`masterPattern`, `slavePattern`, and `patterns` fields use their defaults.
By definitions set within mbsync, these defaults actually specify that
the remote master's `INBOX` mail directory is synchronized to the
local slave's `INBOX` directory.

So, if there is a channel that has no fields specified, then we DO
want to generate its configuration. But if there is a group that has
no channels, then we do NOT generate it.
---
 modules/programs/mbsync.nix | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/modules/programs/mbsync.nix b/modules/programs/mbsync.nix
index ba51d90b..7bfc4826 100644
--- a/modules/programs/mbsync.nix
+++ b/modules/programs/mbsync.nix
@@ -99,8 +99,8 @@ let
         + "\n";
       # Given the group name, and a attr set of channels within that group,
       # Generate a list of strings for each channels' configuration.
-      genChannelStrings = groupName: channels:
-        mapAttrsToList (channelName: info: genChannelString groupName info) channels;
+      genChannelStrings = groupName: channels: optionals (channels != { })
+        (mapAttrsToList (channelName: info: genChannelString groupName info) channels);
       # Given a group, return a string that configures all the channels within
       # the group.
       genGroupsChannels = group: concatStrings
@@ -117,11 +117,11 @@ let
       # make "Channel <grpName>-<chnName>" for each channel to list os strings
       genChannelStrings = groupName: channels: mapAttrsToList
         (name: info: "Channel ${groupName}-${name}") channels;
-      # Take in 1 group, construct the "Group <grpName>" header, and construct
-      # each of the channels.
-      genGroupChannelString = group:
-        [("Group " + group.name)] ++
-        (genChannelStrings group.name group.channels);
+      # Take in 1 group, construct the "Group <grpName>" header, and if the group
+      # is NOT empty, construct each of the channels.
+      genGroupChannelString = group: optionals (groups != { })
+        ([("Group " + group.name)] ++
+         (genChannelStrings group.name group.channels));
       # Given set of groups, generates list of strings, where each string is one
       # of the groups and its consituent channels.
       genGroupsStrings = mapAttrsToList (name: info: concatStringsSep "\n"