unison: add module

modules/misc/news.nix

@@ -1260,6 +1260,14 @@ in
           A new module is available: 'services.password-store-sync'.
         '';
       }
+
+      {
+        time = "2019-11-29T22:46:49+00:00";
+        condition = hostPlatform.isLinux;
+        message = ''
+          A new module is available: 'services.unison'.
+        '';
+      }
     ];
   };
 }

modules/modules.nix

@@ -142,6 +142,7 @@ let
     (loadModule ./services/taskwarrior-sync.nix { condition = hostPlatform.isLinux; })
     (loadModule ./services/udiskie.nix { })
     (loadModule ./services/unclutter.nix { })
+    (loadModule ./services/unison.nix { condition = hostPlatform.isLinux; })
     (loadModule ./services/window-managers/awesome.nix { })
     (loadModule ./services/window-managers/i3.nix { })
     (loadModule ./services/window-managers/xmonad.nix { })

modules/services/unison.nix

@@ -0,0 +1,128 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.services.unison;
+
+  pairOf = t:
+    let
+      list = types.addCheck (types.listOf t) (l: length l == 2);
+    in
+      list // { description = list.description + " of length 2"; };
+
+  pairOptions = {
+    options = {
+      stateDirectory = mkOption {
+        type = types.path;
+        default = "${config.xdg.dataHome}/unison";
+        defaultText = "$XDG_DATA_HOME/unison";
+        description = ''
+          Unison state directory to use.
+        '';
+      };
+
+      commandOptions = mkOption rec {
+        type = with types; attrsOf str;
+        apply = mergeAttrs default;
+        default = {
+          repeat = "watch";
+          sshcmd = "${pkgs.openssh}/bin/ssh";
+          ui = "text";
+          auto = "true";
+          batch = "true";
+          log = "false"; # don't log to file, handled by systemd
+        };
+        description = ''
+          Additional command line options as a dictionary to pass to the
+          <literal>unison</literal> program.
+          </para><para>
+          See
+          <citerefentry>
+            <refentrytitle>unison</refentrytitle>
+            <manvolnum>1</manvolnum>
+          </citerefentry>
+          for a list of available options.
+        '';
+      };
+
+      roots = mkOption {
+        type = pairOf types.str;
+        example = literalExample ''
+          [
+            "/home/user/documents"
+            "ssh://remote/documents"
+          ]
+        '';
+        description = ''
+          Pair of roots to synchronise.
+        '';
+      };
+    };
+  };
+
+  serialiseArg = key: val: "-${key}=${escapeShellArg val}";
+
+  serialiseArgs = args:
+    concatStringsSep " " (mapAttrsToList serialiseArg args);
+
+  makeDefs = gen:
+    mapAttrs'
+      (name: pairCfg: nameValuePair "unison-pair-${name}" (gen name pairCfg))
+      cfg.pairs;
+
+in
+
+{
+  meta.maintainers = with maintainers; [ pacien ];
+
+  options.services.unison = {
+    enable = mkEnableOption "Unison synchronisation";
+
+    pairs = mkOption {
+      type = with types; attrsOf (submodule pairOptions);
+      default = { };
+      example = literalExample ''
+        {
+          roots = [
+            "/home/user/documents"
+            "ssh://remote/documents"
+          ];
+        }
+      '';
+      description = ''
+        Unison root pairs to keep synchronised.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.user.services = makeDefs (name: pairCfg: {
+      Unit = {
+        Description = "Unison pair sync (${name})";
+        # Retry forever, useful in case of network disruption.
+        StartLimitIntervalSec = 0;
+      };
+
+      Service = {
+        Restart = "always";
+        RestartSec = 60;
+
+        CPUSchedulingPolicy = "idle";
+        IOSchedulingClass = "idle";
+
+        Environment = [ "UNISON='${toString pairCfg.stateDirectory}'" ];
+        ExecStart = ''
+          ${pkgs.unison}/bin/unison \
+            ${serialiseArgs pairCfg.commandOptions} \
+            ${strings.concatMapStringsSep " " escapeShellArg pairCfg.roots}
+        '';
+      };
+
+      Install = {
+        WantedBy = [ "default.target" ];
+      };
+    });
+  };
+}