Stop watching hidden and closed views and panels

This prevents exceptions being logged every time a view or a panel is
closed (latter don't seem to trigger on_close).

Author: mheinzler

trailing_spaces.py

@@ -473,7 +473,16 @@ def on_pre_save(self, view):
         if ts_settings.get("trailing_spaces_trim_on_save"):
             view.run_command("delete_trailing_spaces")
 
+    def on_close(self, view):
+        # untrack
+        active_views.pop(view.id(), None)
+
     def update_on_region_change(self, view):
+        # remove views not currently visible
+        if not self.is_view_visible(view):
+            active_views.pop(view.id(), None)
+            return
+
         # compare the currently visible region to the previous (if any) and
         # update if there were changes
         if view.visible_region() != active_views.get(view.id(), view.visible_region()):
@@ -500,6 +509,34 @@ def freeze_last_version(self, view):
             with codecs.open(file_name, "r", "utf-8") as f:
                 on_disk = f.read().splitlines()
 
+    def is_view_visible(self, view):
+        window = view.window()
+        if not window:
+            return False
+
+        # panel views don't trigger on_close but are also not valid anymore
+        # after being hidden, so try to detect these cases here
+        if view.size() == 0 and not view.file_name():
+            return False
+
+        # see if this view is visible in its group
+        group = window.get_view_index(view)[0]
+        if group != -1:
+            return view.id() == window.active_view_in_group(group).id()
+
+        # check if this view is the active panel
+        active_panel = window.active_panel() or ""
+
+        # find_output_panel only works without the "output."" prefix
+        if active_panel.startswith("output."):
+            active_panel = active_panel[len("output."):]
+
+        panel_view = window.find_output_panel(active_panel)
+        if panel_view and view.id() == panel_view.id():
+            return True
+
+        return False
+
 
 # Public: Deletes the trailing spaces.
 class DeleteTrailingSpacesCommand(sublime_plugin.TextCommand):