naughty: Add a `message` widget.

It tracks the notification message.

lib/naughty/widget/init.lua

@@ -5,6 +5,7 @@
 ---------------------------------------------------------------------------
 
 return {
-    title = require( "naughty.widget.title"     );
-    icon  = require( "naughty.widget.icon"      );
+    title   = require( "naughty.widget.title"   );
+    icon    = require( "naughty.widget.icon"    );
+    message = require( "naughty.widget.message" );
 }

lib/naughty/widget/message.lua

@@ -0,0 +1,86 @@
+----------------------------------------------------------------------------
+--- A notification content message.
+--
+-- This widget is a specialized `wibox.widget.textbox` with the following extra
+-- features:
+--
+-- * Honor the `beautiful` notification variables.
+-- * React to the `naughty.notification` object message changes.
+--
+--@DOC_wibox_nwidget_message_simple_EXAMPLE@
+--
+-- @author Emmanuel Lepage Vallee <elv1313@gmail.com>
+-- @copyright 2017 Emmanuel Lepage Vallee
+-- @widgetmod naughty.widget.message
+-- @see wibox.widget.textbox
+----------------------------------------------------------------------------
+local textbox = require("wibox.widget.textbox")
+local gtable  = require("gears.table")
+local beautiful = require("beautiful")
+
+local message = {}
+
+local function markup(notif, wdg)
+    local ret = notif.message or ""
+    local fg = notif.fg or beautiful.notification_fg
+
+    wdg:set_font(notif.font or beautiful.notification_font)
+
+    if fg then
+        ret = "<span color='" .. fg .. "'>" .. ret .. "</span>"
+    end
+
+    return ret
+end
+
+--- The attached notification.
+-- @property notification
+-- @tparam naughty.notification notification
+
+function message:set_notification(notif)
+    if self._private.notification == notif then return end
+
+    if self._private.notification then
+        self._private.notification:disconnect_signal("poperty::message",
+            self._private.message_changed_callback)
+        self._private.notification:disconnect_signal("poperty::fg",
+            self._private.message_changed_callback)
+    end
+
+    self:set_markup(markup(notif, self))
+
+    self._private.notification = notif
+
+    notif:connect_signal("poperty::message", self._private.message_changed_callback)
+    notif:connect_signal("poperty::fg"     , self._private.message_changed_callback)
+end
+
+--- Create a new naughty.widget.message.
+-- @tparam table args
+-- @tparam naughty.notification args.notification The notification.
+-- @constructorfct naughty.widget.message
+
+local function new(args)
+    args = args or {}
+    local tb = textbox()
+    tb:set_wrap("word")
+    tb:set_font(beautiful.notification_font)
+
+    gtable.crush(tb, message, true)
+
+    function tb._private.message_changed_callback()
+        tb:set_markup(markup(tb._private.notification, tb))
+    end
+
+    if args.notification then
+        tb:set_notification(args.notification)
+    end
+
+    return tb
+end
+
+--@DOC_widget_COMMON@
+
+--@DOC_object_COMMON@
+
+return setmetatable(message, {__call = function(_, ...) return new(...) end})