xsession: deprecate xsession.windowManager

The intention is for the `xsession.windowManager` option to be
available for full modules in the future. The option
`xsession.windowManager.command` should now be used to specify the
window manager startup command.

modules/misc/news.nix

@@ -232,12 +232,29 @@ in
           tool in that NIX_AUTO_INSTALL is not supported.
         '';
       }
+
       {
         time = "2017-09-28T12:39:36+00:00";
         message = ''
           A new program module is available: 'programs.rofi';
         '';
       }
+
+      {
+        time = "2017-09-28T21:39:45+00:00";
+        condition =
+          config.xsession.enable
+          && config.xsession.windowManager.usesDeprecated;
+        message = ''
+          The 'xsession.windowManager' option is now deprecated,
+          please use 'xsession.windowManager.command' instead.
+
+          This change was made to prepare for window manager modules
+          under the 'xsession.windowManager' namespace. For example,
+          'xsession.windowManager.xmonad' and
+          'xsession.windowManager.i3'.
+        '';
+      }
     ];
   };
 }

modules/xsession.nix

@@ -6,6 +6,32 @@ let
 
   cfg = config.xsession;
 
+  # Hack to support xsession.windowManager.command option.
+  wmBaseModule = {
+    options = {
+      command = mkOption {
+        type = types.str;
+        example = literalExample ''
+          let
+            xmonad = pkgs.xmonad-with-packages.override {
+              packages = self: [ self.xmonad-contrib self.taffybar ];
+            };
+          in
+            "''${xmonad}/bin/xmonad";
+        '';
+        description = ''
+          Window manager start command.
+        '';
+      };
+
+      usesDeprecated = mkOption {
+        internal = true;
+        type = types.bool;
+        default = false;
+      };
+    };
+  };
+
 in
 
 {
@@ -16,16 +42,15 @@ in
       enable = mkEnableOption "X Session";
 
       windowManager = mkOption {
-        type = types.str;
-        example = literalExample ''
-          let
-            xmonad = pkgs.xmonad-with-packages.override {
-              packages = self: [ self.xmonad-contrib self.taffybar ];
-            };
-          in
-            "''${xmonad}/bin/xmonad";
+        type =
+          types.coercedTo
+            types.str
+            (command: { inherit command; usesDeprecated = true; })
+            (types.submodule wmBaseModule);
+        description = ''
+          Window manager start command. DEPRECATED: Use
+          <varname>xsession.windowManager.command</varname> instead.
         '';
-        description = "Path to window manager to exec.";
       };
 
       initExtra = mkOption {
@@ -36,75 +61,84 @@ in
     };
   };
 
-  config = mkIf cfg.enable {
-    systemd.user.services.setxkbmap = {
-      Unit = {
-        Description = "Set up keyboard in X";
-        After = [ "graphical-session-pre.target" ];
-        PartOf = [ "graphical-session.target" ];
+  config = mkIf cfg.enable (mkMerge [
+    (mkIf cfg.windowManager.usesDeprecated {
+      warnings = [
+        ("xsession.windowManager is deprecated, "
+          + "please use xsession.windowManager.command")
+      ];
+    })
+
+    {
+      systemd.user.services.setxkbmap = {
+        Unit = {
+          Description = "Set up keyboard in X";
+          After = [ "graphical-session-pre.target" ];
+          PartOf = [ "graphical-session.target" ];
+        };
+
+        Install = {
+          WantedBy = [ "graphical-session.target" ];
+        };
+
+        Service = {
+          Type = "oneshot";
+          ExecStart =
+            let
+              args = concatStringsSep " " (
+                [
+                  "-layout '${config.home.keyboard.layout}'"
+                  "-variant '${config.home.keyboard.variant}'"
+                ] ++
+                (map (v: "-option '${v}'") config.home.keyboard.options)
+              );
+            in
+              "${pkgs.xorg.setxkbmap}/bin/setxkbmap ${args}";
+        };
       };
 
-      Install = {
-        WantedBy = [ "graphical-session.target" ];
+      # A basic graphical session target for Home Manager.
+      systemd.user.targets.hm-graphical-session = {
+        Unit = {
+          Description = "Home Manager X session";
+          Requires = [ "graphical-session-pre.target" ];
+          BindsTo = [ "graphical-session.target" ];
+        };
       };
 
-      Service = {
-        Type = "oneshot";
-        ExecStart =
-          let
-            args = concatStringsSep " " (
-              [
-                "-layout '${config.home.keyboard.layout}'"
-                "-variant '${config.home.keyboard.variant}'"
-              ] ++
-              (map (v: "-option '${v}'") config.home.keyboard.options)
-            );
-          in
-            "${pkgs.xorg.setxkbmap}/bin/setxkbmap ${args}";
+      home.file.".xsession" = {
+        mode = "555";
+        text = ''
+          if [[ -e "$HOME/.profile" ]]; then
+            . "$HOME/.profile"
+          fi
+
+          # If there are any running services from a previous session.
+          systemctl --user stop graphical-session.target graphical-session-pre.target
+
+          systemctl --user import-environment DBUS_SESSION_BUS_ADDRESS
+          systemctl --user import-environment DISPLAY
+          systemctl --user import-environment SSH_AUTH_SOCK
+          systemctl --user import-environment XAUTHORITY
+          systemctl --user import-environment XDG_DATA_DIRS
+          systemctl --user import-environment XDG_RUNTIME_DIR
+          systemctl --user import-environment XDG_SESSION_ID
+
+          systemctl --user start hm-graphical-session.target
+
+          ${cfg.initExtra}
+
+          ${cfg.windowManager.command}
+
+          systemctl --user stop graphical-session.target
+          systemctl --user stop graphical-session-pre.target
+
+          # Wait until the units actually stop.
+          while [[ -n "$(systemctl --user --no-legend --state=deactivating list-units)" ]]; do
+            sleep 0.5
+          done
+        '';
       };
-    };
-
-    # A basic graphical session target for Home Manager.
-    systemd.user.targets.hm-graphical-session = {
-      Unit = {
-        Description = "Home Manager X session";
-        Requires = [ "graphical-session-pre.target" ];
-        BindsTo = [ "graphical-session.target" ];
-      };
-    };
-
-    home.file.".xsession" = {
-      mode = "555";
-      text = ''
-        if [[ -e "$HOME/.profile" ]]; then
-          . "$HOME/.profile"
-        fi
-
-        # If there are any running services from a previous session.
-        systemctl --user stop graphical-session.target graphical-session-pre.target
-
-        systemctl --user import-environment DBUS_SESSION_BUS_ADDRESS
-        systemctl --user import-environment DISPLAY
-        systemctl --user import-environment SSH_AUTH_SOCK
-        systemctl --user import-environment XAUTHORITY
-        systemctl --user import-environment XDG_DATA_DIRS
-        systemctl --user import-environment XDG_RUNTIME_DIR
-        systemctl --user import-environment XDG_SESSION_ID
-
-        systemctl --user start hm-graphical-session.target
-
-        ${cfg.initExtra}
-
-        ${cfg.windowManager}
-
-        systemctl --user stop graphical-session.target
-        systemctl --user stop graphical-session-pre.target
-
-        # Wait until the units actually stop.
-        while [[ -n "$(systemctl --user --no-legend --state=deactivating list-units)" ]]; do
-          sleep 0.5
-        done
-      '';
-    };
-  };
+    }
+  ]);
 }