Improved Metadata deepcopy recursion fix.

It was possible for the recursion to occur if mi.deepcopy() was called after (un)safe_format(). Change the state save/restore mechanism to ensure all instance variables are restored to base settings.

src/calibre/utils/formatter.py

@@ -1827,29 +1827,12 @@ def evaluate(self, fmt, args, kwargs, global_vars, break_reporter=None):
  # reference can use different parameters when calling safe_format(). Because
  # the parameters are saved as instance variables they can possibly affect
  # the 'calling' template. To avoid this problem, save the current formatter
- # state when recursion is detected. There is no point in saving the level
- # 0 state.
+ # state when recursion is detected. Save state at level zero to be sure that
+ # all class instance variables are restored to their base settings.
 
  def save_state(self):
  self.recursion_level += 1
- if self.recursion_level > 0:
- return (
- (self.strip_results,
- self.column_name,
- self.template_cache,
- self.kwargs,
- self.book,
- self.global_vars,
- self.funcs,
- self.locals,
- self._caller,
- self.python_context_object))
- else:
- return None
-
- def restore_state(self, state):
- self.recursion_level -= 1
- if state is not None:
+ return (
  (self.strip_results,
  self.column_name,
  self.template_cache,
@@ -1859,7 +1842,22 @@ def restore_state(self, state):
  self.funcs,
  self.locals,
  self._caller,
- self.python_context_object) = state
+ self.python_context_object))
+
+ def restore_state(self, state):
+ self.recursion_level -= 1
+ if state is None:
+ raise ValueError(_('Formatter state restored before saved'))
+ (self.strip_results,
+ self.column_name,
+ self.template_cache,
+ self.kwargs,
+ self.book,
+ self.global_vars,
+ self.funcs,
+ self.locals,
+ self._caller,
+ self.python_context_object) = state
 
  # Allocate an interpreter if the formatter encounters a GPM or TPM template.
  # We need to allocate additional interpreters if there is composite recursion