mbsync: Adds extraConfig.{local|remote}

... to be able to limit the number of mails to be retrieved.
local refers to the "store" configuration, remote to the "channel".

modules/programs/mbsync-accounts.nix

@@ -2,6 +2,9 @@
 
 with lib;
 
+let
+  extraConfigType = with lib.types; attrsOf (either (either str int) bool);
+in
 {
   options.mbsync = {
     enable = mkEnableOption "synchronization using mbsync";
@@ -53,5 +56,27 @@ with lib;
         Pattern of mailboxes to synchronize.
       '';
     };
+
+    extraConfig.local = mkOption {
+      type = extraConfigType;
+      default = {};
+      description = ''
+        Per store extra config.
+      '';
+    };
+
+    extraConfig.remote = mkOption {
+      type = extraConfigType;
+      default = {};
+      example = literalExample ''
+        {
+          MaxMessages = 10000;
+          MaxSize = 1m;
+        };
+      '';
+      description = ''
+        Per channel extra config.
+      '';
+    };
   };
 }

modules/programs/mbsync.nix

@@ -33,10 +33,13 @@ let
   genSection = header: entries:
     let
       escapeValue = escape [ "\"" ];
+      hasSpace = v: builtins.match ".* .*" v != null;
       genValue = v:
         if isList v
         then concatMapStringsSep " " genValue v
-        else "\"${escapeValue v}\"";
+        else if isInt v then toString v
+        else if (hasSpace v) then "\"${escapeValue v}\""
+        else v;
     in
       ''
         ${header}
@@ -70,11 +73,12 @@ let
           Inbox = "${maildir.absPath}/${folders.inbox}";
           SubFolders = "Verbatim";
         }
-        //
-        optionalAttrs (mbsync.flatten != null) { Flatten = mbsync.flatten; }
+        // optionalAttrs (mbsync.flatten != null) { Flatten = mbsync.flatten; }
+        // mbsync.extraConfig.local
       )
       + "\n"
-      + genSection "Channel ${name}" {
+      + genSection "Channel ${name}" (
+        {
           Master = ":${name}-remote:";
           Slave = ":${name}-local:";
           Patterns = mbsync.patterns;
@@ -83,6 +87,8 @@ let
           Expunge = masterSlaveMapping.${mbsync.expunge};
           SyncState = "*";
         }
+        // mbsync.extraConfig.remote
+      )
       + "\n";
 
   genGroupConfig = name: channels: