naughty: Only enable the legacy mode when there is no other handlers.

It was called legacy for a reason, it is meant to be used only when the
rc.lua doesn't have the newer notification section.

lib/naughty/core.lua

@@ -122,6 +122,10 @@ gtable.crush(naughty, require("naughty.constants"))
 -- @property active
 -- @param table
 
+--- True when there is a handler connected to `request::display`.
+-- @property has_display_handler
+-- @param boolean
+
 local properties = {
     suspended         = false,
     expiration_paused = false
@@ -346,6 +350,10 @@ function naughty.get_active()
     return naughty._active
 end
 
+function naughty.get_has_display_handler()
+    return conns["request::display"] and #conns["request::display"] > 0 or false
+end
+
 --- Set new notification timeout.
 --
 -- This function is deprecated, use `notification:reset_timeout(new_timeout)`.
@@ -454,7 +462,7 @@ end
 
 --- Emitted when a notification has to be displayed.
 --
--- To add an handler, use:
+-- To add a handler, use:
 --
 --    naughty.connect_signal("request::display", function(notification, args)
 --        -- do something

lib/naughty/layout/legacy.lua

@@ -279,23 +279,10 @@ end
 
 naughty.connect_signal("destroyed", cleanup)
 
---- The default notification GUI handler.
---
--- To disable this handler, use:
---
---    naughty.disconnect_signal(
---        "request::display", naughty.default_notification_handler
---    )
---
--- It looks like:
---
---@DOC_naughty_actions_EXAMPLE@
---
--- @tparam table notification The `naughty.notification` object.
--- @tparam table args Any arguments passed to the `naughty.notify` function,
---  including, but not limited to all `naughty.notification` properties.
--- @signalhandler naughty.default_notification_handler
 function naughty.default_notification_handler(notification, args)
+    -- This is a fallback for users whose config doesn't have the newer
+    -- `request::display` section.
+    if naughty.has_display_handler then return end
 
     -- If request::display is called more than once, simply make sure the wibox
     -- is visible.
@@ -561,4 +548,4 @@ function naughty.default_notification_handler(notification, args)
     end
 end
 
-naughty.connect_signal("request::display", naughty.default_notification_handler)
+naughty.connect_signal("request::fallback", naughty.default_notification_handler)

lib/naughty/notification.lua

@@ -551,7 +551,8 @@ local function create(args)
 
     -- Let all listeners handle the actual visual aspects
     if (not n.ignore) and (not n.preset.ignore) then
-        naughty.emit_signal("request::display", n, args)
+        naughty.emit_signal("request::display" , n, args)
+        naughty.emit_signal("request::fallback", n, args)
     end
 
     -- Because otherwise the setter logic would not be executed