borgmatic: add option for pattern matching

Borgmatic has support for Borg's pattern matching. It is mutually
exclusive with the existing `sourceDirectories` option, so assertions
have been added to make sure that both are not set at the same
time (but also that at least one of them is). Additionally, tests have
been added to test the following configurations: `patterns` instead of
`sourceDirectories`, both at the same time, and neither.

modules/programs/borgmatic.nix

@@ -76,12 +76,39 @@ let
       (mkAfter [ (toString hmExcludeFile) ]);
     options = {
       location = {
-        sourceDirectories = mkOption {
+        sourceDirectories = mkNullableOption {
           type = types.listOf types.str;
-          description = "Directories to backup.";
+          default = null;
+          description = ''
+            Directories to backup.
+
+            Mutually exclusive with [](#opt-programs.borgmatic.backups._name_.location.patterns).
+          '';
           example = literalExpression "[config.home.homeDirectory]";
         };
 
+        patterns = mkNullableOption {
+          type = types.listOf types.str;
+          default = null;
+          description = ''
+            Patterns to include/exclude.
+
+            See the output of `borg help patterns` for the syntax. Pattern paths
+            are relative to `/` even when a different recursion root is set.
+
+            Mutually exclusive with [](#opt-programs.borgmatic.backups._name_.location.sourceDirectories).
+          '';
+          example = literalExpression ''
+            [
+              "R /home/user"
+              "- home/user/.cache"
+              "- home/user/Downloads"
+              "+ home/user/Videos/Important Video"
+              "- home/user/Videos"
+            ]
+          '';
+        };
+
         repositories = mkOption {
           type = types.listOf (types.either types.str repositoryOption);
           apply = cleanRepositories;
@@ -194,6 +221,7 @@ let
   writeConfig = config:
     generators.toYAML { } (removeNullValues ({
       source_directories = config.location.sourceDirectories;
+      patterns = config.location.patterns;
       repositories = config.location.repositories;
       encryption_passcommand = config.storage.encryptionPasscommand;
       keep_within = config.retention.keepWithin;
@@ -247,7 +275,19 @@ in {
     assertions = [
       (lib.hm.assertions.assertPlatform "programs.borgmatic" pkgs
         lib.platforms.linux)
-    ];
+    ] ++ (mapAttrsToList (backup: opts: {
+      assertion = opts.location.sourceDirectories == null
+        || opts.location.patterns == null;
+      message = ''
+        Borgmatic backup configuration "${backup}" cannot specify both 'location.sourceDirectories' and 'location.patterns'.
+      '';
+    }) cfg.backups) ++ (mapAttrsToList (backup: opts: {
+      assertion = !(opts.location.sourceDirectories == null
+        && opts.location.patterns == null);
+      message = ''
+        Borgmatic backup configuration "${backup}" must specify one of 'location.sourceDirectories' or 'location.patterns'.
+      '';
+    }) cfg.backups);
 
     xdg.configFile = with lib.attrsets;
       mapAttrs' (configName: config:

tests/modules/programs/borgmatic/both-sourcedirectories-and-patterns.nix

@@ -0,0 +1,26 @@
+{ config, pkgs, ... }:
+
+let
+
+  backups = config.programs.borgmatic.backups;
+
+in {
+  programs.borgmatic = {
+    enable = true;
+    backups = {
+      main = {
+        location = {
+          sourceDirectories = [ "/my-stuff-to-backup" ];
+          patterns = [ "R /" "+ my-stuff-to-backup" ];
+          repositories = [ "/mnt/disk1" ];
+        };
+      };
+    };
+  };
+
+  test.stubs.borgmatic = { };
+
+  test.asserts.assertions.expected = [''
+    Borgmatic backup configuration "main" cannot specify both 'location.sourceDirectories' and 'location.patterns'.
+  ''];
+}

tests/modules/programs/borgmatic/default.nix

@@ -1,5 +1,10 @@
 {
   borgmatic-program-basic-configuration = ./basic-configuration.nix;
+  borgmatic-program-patterns-configuration = ./patterns-configuration.nix;
+  borgmatic-program-both-sourcedirectories-and-patterns =
+    ./both-sourcedirectories-and-patterns.nix;
+  borgmatic-program-neither-sourcedirectories-nor-patterns =
+    ./neither-sourcedirectories-nor-patterns.nix;
   borgmatic-program-include-hm-symlinks = ./include-hm-symlinks.nix;
   borgmatic-program-exclude-hm-symlinks = ./exclude-hm-symlinks.nix;
   borgmatic-program-exclude-hm-symlinks-nothing-else =

tests/modules/programs/borgmatic/neither-sourcedirectories-nor-patterns.nix

@@ -0,0 +1,18 @@
+{ config, pkgs, ... }:
+
+let
+
+  backups = config.programs.borgmatic.backups;
+
+in {
+  programs.borgmatic = {
+    enable = true;
+    backups = { main = { location = { repositories = [ "/mnt/disk1" ]; }; }; };
+  };
+
+  test.stubs.borgmatic = { };
+
+  test.asserts.assertions.expected = [''
+    Borgmatic backup configuration "main" must specify one of 'location.sourceDirectories' or 'location.patterns'.
+  ''];
+}

tests/modules/programs/borgmatic/patterns-configuration.nix

@@ -0,0 +1,58 @@
+{ config, pkgs, ... }:
+
+let
+
+  boolToString = bool: if bool then "true" else "false";
+  backups = config.programs.borgmatic.backups;
+
+in {
+  programs.borgmatic = {
+    enable = true;
+    backups = {
+      main = {
+        location = {
+          patterns = [
+            "R /home/user"
+            "+ home/user/stuff-to-backup"
+            "+ home/user/junk/important-file"
+            "- home/user/junk"
+          ];
+          repositories = [ "/mnt/backup-drive" ];
+        };
+      };
+    };
+  };
+
+  test.stubs.borgmatic = { };
+
+  nmt.script = ''
+    config_file=$TESTED/home-files/.config/borgmatic.d/main.yaml
+    assertFileExists $config_file
+
+    declare -A expectations
+
+    expectations[patterns[0]]="${
+      builtins.elemAt backups.main.location.patterns 0
+    }"
+    expectations[patterns[1]]="${
+      builtins.elemAt backups.main.location.patterns 1
+    }"
+    expectations[patterns[2]]="${
+      builtins.elemAt backups.main.location.patterns 2
+    }"
+    expectations[patterns[3]]="${
+      builtins.elemAt backups.main.location.patterns 3
+    }"
+
+    yq=${pkgs.yq-go}/bin/yq
+
+    for filter in "''${!expectations[@]}"; do
+      expected_value="''${expectations[$filter]}"
+      actual_value="$($yq ".$filter" $config_file)"
+
+      if [[ "$actual_value" != "$expected_value" ]]; then
+        fail "Expected '$filter' to be '$expected_value' but was '$actual_value'"
+      fi
+    done
+  '';
+}