Added check to ensure we are in lighttable view prior to callling darktable.register_lib. If darktable was invoked in single image (darkroom) mode, then an event handler is registered to detect the change from darkroom mode to lighttable mode so that we can then call darktable.register_lib.

contrib/copy_attach_detach_tags.lua

@@ -51,6 +51,11 @@ local function _(msgid)
     return gettext.dgettext("copy_attach_detach_tags", msgid)
 end
 
+local cadt = {}
+cadt.module_installed = false
+cadt.event_registered = false
+cadt.widget_table = {}
+
 
 local image_tags = {}
 
@@ -156,6 +161,26 @@ local function replace_tags()
   dt.print(_('Tags replaced'))
 end
 
+local function install_module()
+  if not cadt.module_installed then
+    dt.register_lib("tagging_addon","Tagging addon",true,true,{
+        [dt.gui.views.lighttable] = {"DT_UI_CONTAINER_PANEL_RIGHT_CENTER",500}
+        },
+        dt.new_widget("box") {
+      --    orientation = "vertical",
+          reset_callback = function()
+                        taglist_label.label = ""
+                        image_tags = {}
+                        end,
+          table.unpack(cadt.widget_table),
+          },
+       nil,
+       nil
+      )
+    cadt.module_installed = true
+  end
+end
+
 -- create modul Tagging addons
 taglist_label.reset_callback = mcopy_tags
 
@@ -190,31 +215,31 @@ local box2 = dt.new_widget("box"){
 local sep = dt.new_widget("separator"){}
 
 -- pack elements into widget table for a nicer layout
-local widget_table = {}
 
-widget_table[1] = box1
-widget_table[#widget_table+1] = box2
+cadt.widget_table[1] = box1
+cadt.widget_table[#cadt.widget_table+1] = box2
 
-widget_table[#widget_table+1] = sep
-widget_table[#widget_table+1] = taglabel
-widget_table[#widget_table+1] = taglist_label
+cadt.widget_table[#cadt.widget_table+1] = sep
+cadt.widget_table[#cadt.widget_table+1] = taglabel
+cadt.widget_table[#cadt.widget_table+1] = taglist_label
 
 
 -- create modul
-dt.register_lib("tagging_addon","Tagging addon",true,true,{
-    [dt.gui.views.lighttable] = {"DT_UI_CONTAINER_PANEL_RIGHT_CENTER",500}
-    },
-    dt.new_widget("box") {
-  --    orientation = "vertical",
-      reset_callback = function()
-                    taglist_label.label = ""
-                    image_tags = {}
-                    end,
-      table.unpack(widget_table),
-      },
-   nil,
-   nil
-  )
+if dt.gui.current_view().name == "lighttable" then
+  install_module()
+else
+  if not cadt.event_registered then
+    dt.register_event(
+      "view-changed",
+      function(event, old_view, new_view)
+        if new_view.name == "lighttable" and old_view.name == "darkroom" then
+          install_module()
+         end
+      end
+    )
+    cadt.event_registered = true
+  end
+end
 
 
 -- shortcut for copy