Bug #1928548: Error opening template functions preference. Part of a fix, ensuring that the exception doesn't leave the ghost dialog.

src/calibre/gui2/preferences/__init__.py

@@ -59,7 +59,8 @@ class ConfigWidgetInterface(object):
     def initialize(self):
         '''
         Should set all config values to their initial values (the values
-        stored in the config files).
+        stored in the config files). A "return" statement is optional. Return
+        False if the dialog is not to be shown.
         '''
         raise NotImplementedError()
 

src/calibre/gui2/preferences/main.py

@@ -310,7 +310,9 @@ class Preferences(QDialog):
     def show_plugin(self, plugin):
         self.showing_widget = plugin.create_widget(self.scroll_area)
         self.showing_widget.genesis(self.gui)
-        self.showing_widget.initialize()
+        x = self.showing_widget.initialize()
+        if isinstance(x, bool) and not x:
+            return
         self.set_tooltips_for_labels()
         self.scroll_area.setWidget(self.showing_widget)
         self.stack.setCurrentIndex(1)

src/calibre/gui2/preferences/template_functions.py

@@ -5,7 +5,7 @@
 import copy, json, traceback
 from qt.core import QDialogButtonBox, QDialog
 
-from calibre.gui2 import error_dialog, warning_dialog
+from calibre.gui2 import error_dialog, warning_dialog, question_dialog
 from calibre.gui2.dialogs.template_dialog import TemplateDialog
 from calibre.gui2.preferences import ConfigWidgetBase, test_widget
 from calibre.gui2.preferences.template_functions_ui import Ui_Form
@@ -149,9 +149,20 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
         self.builtins = formatter_functions().get_builtins_and_aliases()
 
         self.st_funcs = {}
+        try:
             for v in self.db.prefs.get('user_template_functions', []):
                 if not function_pref_is_python(v):
                     self.st_funcs.update({function_pref_name(v):compile_user_function(*v)})
+        except:
+            ans = question_dialog(self, _('Template functions'),
+                    _('The template functions saved in the library are corrupt. '
+                      "Do you want to delete them? Answering 'Yes' will delete all "
+                      "the functions."), det_msg=traceback.format_exc(),
+                    show_copy_button=True)
+            if ans:
+                print('remove the preference')
+                self.db.prefs['user_template_functions'] = []
+            return False
 
         self.build_function_names_box()
         self.function_name.currentIndexChanged[native_string_type].connect(self.function_index_changed)