nixos/restic: add exclude parameter

This provides an easy way to specify exclude patterns in config. It was
already possible via extraBackupOptions; this change creates a simpler,
similar to other backup services, way to specify them.

nixos/modules/services/backup/restic.nix

@@ -126,6 +126,21 @@ in
           ];
         };
 
+        exclude = mkOption {
+          type = types.listOf types.str;
+          default = [ ];
+          description = lib.mdDoc ''
+            Patterns to exclude when backing up. See
+            https://restic.readthedocs.io/en/latest/040_backup.html#excluding-files for
+            details on syntax.
+          '';
+          example = [
+            "/var/cache"
+            "/home/*/.cache"
+            ".git"
+          ];
+        };
+
         timerConfig = mkOption {
           type = types.attrsOf unitOption;
           default = {
@@ -249,6 +264,7 @@ in
     example = {
       localbackup = {
         paths = [ "/home" ];
+        exclude = [ "/home/*/.cache" ];
         repository = "/mnt/backup-hdd";
         passwordFile = "/etc/nixos/secrets/restic-password";
         initialize = true;
@@ -280,6 +296,7 @@ in
           let
             extraOptions = concatMapStrings (arg: " -o ${arg}") backup.extraOptions;
             resticCmd = "${backup.package}/bin/restic${extraOptions}";
+            excludeFlags = if (backup.exclude != []) then ["--exclude-file=${pkgs.writeText "exclude-patterns" (concatStringsSep "\n" backup.exclude)}"] else [];
             filesFromTmpFile = "/run/restic-backups-${name}/includes";
             backupPaths =
               if (backup.dynamicFilesFrom == null)
@@ -315,7 +332,7 @@ in
             restartIfChanged = false;
             serviceConfig = {
               Type = "oneshot";
-              ExecStart = (optionals (backupPaths != "") [ "${resticCmd} backup --cache-dir=%C/restic-backups-${name} ${concatStringsSep " " backup.extraBackupArgs} ${backupPaths}" ])
+              ExecStart = (optionals (backupPaths != "") [ "${resticCmd} backup --cache-dir=%C/restic-backups-${name} ${concatStringsSep " " (backup.extraBackupArgs ++ excludeFlags)} ${backupPaths}" ])
                 ++ pruneCmd;
               User = backup.user;
               RuntimeDirectory = "restic-backups-${name}";

nixos/tests/restic.nix

@@ -27,6 +27,7 @@ import ./make-test-python.nix (
 
     passwordFile = "${pkgs.writeText "password" "correcthorsebatterystaple"}";
     paths = [ "/opt" ];
+    exclude = [ "/opt/excluded_file_*" ];
     pruneOpts = [
       "--keep-daily 2"
       "--keep-weekly 1"
@@ -47,17 +48,17 @@ import ./make-test-python.nix (
         {
           services.restic.backups = {
             remotebackup = {
-              inherit passwordFile paths pruneOpts backupPrepareCommand backupCleanupCommand;
+              inherit passwordFile paths exclude pruneOpts backupPrepareCommand backupCleanupCommand;
               repository = remoteRepository;
               initialize = true;
             };
             remote-from-file-backup = {
-              inherit passwordFile paths pruneOpts;
+              inherit passwordFile paths exclude pruneOpts;
               initialize = true;
               repositoryFile = pkgs.writeText "repositoryFile" remoteFromFileRepository;
             };
             rclonebackup = {
-              inherit passwordFile paths pruneOpts;
+              inherit passwordFile paths exclude pruneOpts;
               initialize = true;
               repository = rcloneRepository;
               rcloneConfig = {
@@ -104,6 +105,7 @@ import ./make-test-python.nix (
       server.succeed(
           # set up
           "cp -rT ${testDir} /opt",
+          "touch /opt/excluded_file_1 /opt/excluded_file_2",
           "mkdir -p /tmp/restic-rclone-backup",
 
           # test that remotebackup runs custom commands and produces a snapshot