nixos/backups/restic: handle cases when both dynamicFileFrom and paths are set

Also, add a test to verify that it works.

This change also removes the part of custom package test that verifies
that the correct paths are provided. This is already tested by restore
tests.

Before this change, setting both paths and dynamicFileFrom would cause
paths to be silently ignored. Making that actually apply the obvious
interpretation seems to me to be strictly better than prohibiting the
two from being set at the same time.

1 files changed, 14 insertions, 11 deletions

diff --git a/nixos/modules/services/backup/restic.nix b/nixos/modules/services/backup/restic.nix
index 1620770e5b564..9c5d3b984a87d 100644
--- a/nixos/modules/services/backup/restic.nix
+++ b/nixos/modules/services/backup/restic.nix
@@ -113,12 +113,15 @@ in
         };
 
         paths = mkOption {
+          # This is nullable for legacy reasons only. We should consider making it a pure listOf
+          # after some time has passed since this comment was added.
           type = types.nullOr (types.listOf types.str);
-          default = null;
+          default = [ ];
           description = lib.mdDoc ''
-            Which paths to backup.  If null or an empty array, no
-            backup command will be run.  This can be used to create a
-            prune-only job.
+            Which paths to backup, in addition to ones specified via
+            `dynamicFilesFrom`.  If null or an empty array and
+            `dynamicFilesFrom` is also null, no backup command will be run.
+             This can be used to create a prune-only job.
           '';
           example = [
             "/var/lib/postgresql"
@@ -231,7 +234,7 @@ in
           description = lib.mdDoc ''
             A script that produces a list of files to back up.  The
             results of this command are given to the '--files-from'
-            option.
+            option. The result is merged with paths specified via `paths`.
           '';
           example = "find /home/matt/git -type d -name .git";
         };
@@ -300,10 +303,7 @@ in
             resticCmd = "${backup.package}/bin/restic${extraOptions}";
             excludeFlags = optional (backup.exclude != []) "--exclude-file=${pkgs.writeText "exclude-patterns" (concatStringsSep "\n" backup.exclude)}";
             filesFromTmpFile = "/run/restic-backups-${name}/includes";
-            backupPaths =
-              if (backup.dynamicFilesFrom == null)
-              then optionalString (backup.paths != null) (concatStringsSep " " backup.paths)
-              else "--files-from ${filesFromTmpFile}";
+            doBackup = (backup.dynamicFilesFrom != null) || (backup.paths != null && backup.paths != []);
             pruneCmd = optionals (builtins.length backup.pruneOpts > 0) [
               (resticCmd + " forget --prune " + (concatStringsSep " " backup.pruneOpts))
               (resticCmd + " check " + (concatStringsSep " " backup.checkOpts))
@@ -335,7 +335,7 @@ in
             restartIfChanged = false;
             serviceConfig = {
               Type = "oneshot";
-              ExecStart = (optionals (backupPaths != "") [ "${resticCmd} backup ${concatStringsSep " " (backup.extraBackupArgs ++ excludeFlags)} ${backupPaths}" ])
+              ExecStart = (optionals doBackup [ "${resticCmd} backup ${concatStringsSep " " (backup.extraBackupArgs ++ excludeFlags)} --files-from=${filesFromTmpFile}" ])
                 ++ pruneCmd;
               User = backup.user;
               RuntimeDirectory = "restic-backups-${name}";
@@ -353,8 +353,11 @@ in
               ${optionalString (backup.initialize) ''
                 ${resticCmd} snapshots || ${resticCmd} init
               ''}
+              ${optionalString (backup.paths != null && backup.paths != []) ''
+                cat ${pkgs.writeText "staticPaths" (concatStringsSep "\n" backup.paths)} >> ${filesFromTmpFile}
+              ''}
               ${optionalString (backup.dynamicFilesFrom != null) ''
-                ${pkgs.writeScript "dynamicFilesFromScript" backup.dynamicFilesFrom} > ${filesFromTmpFile}
+                ${pkgs.writeScript "dynamicFilesFromScript" backup.dynamicFilesFrom} >> ${filesFromTmpFile}
               ''}
             '';
           } // optionalAttrs (backup.dynamicFilesFrom != null || backup.backupCleanupCommand != null) {