Fix ticket #8214 (Detect 'senseless' user input)

src/calibre/gui2/preferences/save_template.py

@@ -8,7 +8,7 @@
 
 from PyQt4.Qt import QWidget, pyqtSignal
 
-from calibre.gui2 import error_dialog
+from calibre.gui2 import error_dialog, question_dialog
 from calibre.gui2.preferences.save_template_ui import Ui_Form
 from calibre.library.save_to_disk import FORMAT_ARG_DESCS, preprocess_template
 from calibre.utils.formatter import validation_formatter
@@ -52,7 +52,11 @@ def validate(self):
         '''
         tmpl = preprocess_template(self.opt_template.text())
         try:
-            validation_formatter.validate(tmpl)
+            t = validation_formatter.validate(tmpl)
+            if t.find(validation_formatter._validation_string) < 0:
+                return question_dialog(self, _('Constant template'),
+                    _('The template contains no {fields}, so all '
+                      'books will have the same name. Is this OK?'))
         except Exception, err:
             error_dialog(self, _('Invalid template'),
                     '<p>'+_('The template %s is invalid:')%tmpl + \

src/calibre/utils/formatter.py

@@ -453,7 +453,7 @@ def safe_format(self, fmt, kwargs, error_value, book):
 
 class ValidateFormatter(TemplateFormatter):
     '''
-    Provides a format function that substitutes '' for any missing value
+    Provides a formatter that substitutes the validation string for every value
     '''
     def get_value(self, key, args, kwargs):
         return self._validation_string