bacon: add module

Bacon is a background rust code checker. See
<https://dystroy.org/bacon/>.

modules/programs/bacon.nix

@@ -0,0 +1,37 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.programs.bacon;
+
+  settingsFormat = pkgs.formats.toml { };
+in {
+  meta.maintainers = [ hm.maintainers.shimunn ];
+
+  options.programs.bacon = {
+    enable = mkEnableOption "bacon, a background rust code checker";
+
+    settings = mkOption {
+      type = settingsFormat.type;
+      example = {
+        jobs.default = {
+          command = [ "cargo" "build" "--all-features" "--color" "always" ];
+          need_stdout = true;
+        };
+      };
+      description = ''
+        Bacon configuration.
+        For available settings see <https://dystroy.org/bacon/#global-preferences>.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    home.packages = [ pkgs.bacon ];
+
+    xdg.configFile."bacon/prefs.toml".source =
+      settingsFormat.generate "prefs.toml" cfg.settings;
+  };
+}