1) finish JSON-storage of template function source code

2) fix for #8388. This fix was chosen because it emulates the behavior in 0.7.38, where get_metadata returned empty author lists

src/calibre/gui2/preferences/template_functions.py

@@ -5,7 +5,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
-import traceback
+import json, traceback
 
 from calibre.gui2 import error_dialog
 from calibre.gui2.preferences import ConfigWidgetBase, test_widget
@@ -73,6 +73,12 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
         self.textBrowser.setHtml(help_text)
 
     def initialize(self):
+        try:
+            with open(P('template-functions.json'), 'rb') as f:
+                self.builtin_source_dict = json.load(f, encoding='utf-8')
+        except:
+            self.builtin_source_dict = {}
+
         self.funcs = formatter_functions.get_functions()
         self.builtins = formatter_functions.get_builtins()
 
@@ -179,8 +185,13 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
         func = self.funcs[txt]
         self.argument_count.setValue(func.arg_count)
         self.documentation.setText(func.doc)
-        self.program.setPlainText(func.program_text)
         if txt in self.builtins:
+            if hasattr(func, 'program_text'):
+                self.program.setPlainText(func.program_text)
+            elif txt in self.builtin_source_dict:
+                self.program.setPlainText(self.builtin_source_dict[txt])
+            else:
+                self.program.setPlainText(_('function source code not available'))
             self.documentation.setReadOnly(True)
             self.argument_count.setReadOnly(True)
             self.program.setReadOnly(True)

src/calibre/library/database2.py

@@ -690,6 +690,9 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
         mi = Metadata(None)
 
         aut_list = row[fm['au_map']]
+        if not aut_list:
+            aut_list = []
+        else:
             aut_list = [p.split(':::') for p in aut_list.split(':#:')]
         aum = []
         aus = {}

src/calibre/library/sqlite.py

@@ -100,7 +100,7 @@ class AumSortedConcatenate(object):
         keys = self.ans.keys()
         l = len(keys)
         if l == 0:
-            return 'Unknown:::Unknown'
+            return None
         if l == 1:
             return self.ans[keys[0]]
         return ':#:'.join([self.ans[v] for v in sorted(keys)])