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/quicktag.lua

@@ -47,6 +47,12 @@ local dt = require "darktable"
 local du = require "lib/dtutils"
 local debug = require "darktable.debug"
 
+local qt = {}
+qt.module_installed = false
+qt.event_registered = false
+qt.widget_table = {}
+
+
 
 local gettext = dt.gettext
 
@@ -177,6 +183,27 @@ local function update_quicktag_list()
   end
 end
 
+local function install_module()
+  if not qt.module_installed then
+    dt.register_lib(
+      "quicktag",     -- Module name
+      "quicktag",     -- name
+      true,                -- expandable
+      false,               -- resetable
+      {[dt.gui.views.lighttable] = {"DT_UI_CONTAINER_PANEL_RIGHT_CENTER", 490}},
+
+      dt.new_widget("box"){
+        orientation = "vertical",
+        table.unpack(qt.widget_table),
+
+      },
+      nil,-- view_enter
+      nil -- view_leave
+    )
+    qt.module_installed = true
+  end
+end
+
 update_quicktag_list()
 
 local new_quicktag = dt.new_widget("entry"){
@@ -213,33 +240,32 @@ local new_qt_widget = dt.new_widget ("box") {
 
 -- back UI elements in a table
 -- thanks to wpferguson for the hint
-local widget_table = {}
 
 for i=1,qnr do
-  widget_table[#widget_table  + 1] =  button[i]
+  qt.widget_table[#qt.widget_table  + 1] =  button[i]
 end
 
-widget_table[#widget_table  + 1] = dt.new_widget("separator"){}
-widget_table[#widget_table  + 1] = old_quicktag
-widget_table[#widget_table  + 1] = new_qt_widget
+qt.widget_table[#qt.widget_table  + 1] = dt.new_widget("separator"){}
+qt.widget_table[#qt.widget_table  + 1] = old_quicktag
+qt.widget_table[#qt.widget_table  + 1] = new_qt_widget
 
 
 --create module
-dt.register_lib(
-  "quicktag",     -- Module name
-  "quicktag",     -- name
-  true,                -- expandable
-  false,               -- resetable
-  {[dt.gui.views.lighttable] = {"DT_UI_CONTAINER_PANEL_RIGHT_CENTER", 490}},
-
-  dt.new_widget("box"){
-    orientation = "vertical",
-    table.unpack(widget_table),
-
-  },
-  nil,-- view_enter
-  nil -- view_leave
-)
+if dt.gui.current_view().name == "lighttable" then
+  install_module()
+else
+  if not qt.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
+    )
+    qt.event_registered = true
+  end
+end
 
 -- create shortcuts
 for i=1,qnr do