s-linking: always rescan when the default targets change

The "follow" setting was never really meant to disable reacting to
default target changes. It is also not meant to disable moving normal streams
to follow the default target. It is only meant to control whether streams
with a 'target.object' that matches the default target will move or not
to follow the default target changes (PulseAudio compat thing...)

Even if we leave this code here, disabling the "follow" option may disable
reacting to default target changes, but the streams will be moved anyway
when there is some other change in the graph (i.e. in the next rescan)

src/scripts/linking/move-follow.lua

@@ -11,30 +11,6 @@ log = Log.open_topic ("s-linking")
 settings = require ("settings-linking")
 handles = {}
 
-function handleFollowSetting (enable)
-  if (not handles.follow_hook) and (enable == true) then
-    handles.follow_hook = SimpleEventHook {
-      name = "linking/follow",
-      interests = {
-        EventInterest {
-          Constraint { "event.type", "=", "metadata-changed" },
-          Constraint { "metadata.name", "=", "default" },
-          Constraint { "event.subject.key", "c", "default.audio.source",
-              "default.audio.sink", "default.video.source" },
-        },
-      },
-      execute = function (event)
-        local source = event:get_source ()
-        source:call ("schedule-rescan", "linking")
-      end
-    }
-    handles.follow_hook:register ()
-  elseif (handles.follow_hook) and (enable == false) then
-    handles.follow_hook:remove ()
-    handles.follow_hook = nil
-  end
-end
-
 function handleMoveSetting (enable)
   if (not handles.move_hook) and (enable == true) then
     handles.move_hook = SimpleEventHook {
@@ -58,8 +34,5 @@ function handleMoveSetting (enable)
   end
 end
 
-settings:subscribe ("follow", handleFollowSetting)
-handleFollowSetting (settings.follow)
-
 settings:subscribe ("move", handleMoveSetting)
 handleMoveSetting (settings.move)

src/scripts/linking/rescan.lua

@@ -179,6 +179,13 @@ SimpleEventHook {
       Constraint { "event.type", "=", "device-params-changed" },
       Constraint { "event.subject.param-id", "=", "Route" },
     },
+    -- on any "default" target changed
+    EventInterest {
+      Constraint { "event.type", "=", "metadata-changed" },
+      Constraint { "metadata.name", "=", "default" },
+      Constraint { "event.subject.key", "c", "default.audio.source",
+          "default.audio.sink", "default.video.source" },
+    },
   },
   execute = function (event)
     local source = event:get_source ()