Show local variables from all possibly relevant frames

This doesn't show the variables for a few specific functions, specifically those which have a '_ignore_locals_' local variable set to a truthy value. For now, those functions are handle_error.__call__ (which is present in every traceback ever, due to its nature), cmd.caller and command.caller (one or the other is present in a large number of tracebacks, again due to their nature).

This makes debugging easier when the error is not in the innermost frame, but rather in one or two frames before, and the locals are lost.

src/decorators.py

@@ -27,7 +27,6 @@ HOOKS = defaultdict(list)
 # Error handler decorators and context managers
 
 class _local(threading.local):
-    frame_locals = None
     handler = None
     level = 0
 
@@ -77,28 +76,37 @@ class print_traceback:
             _local.level -= 1
             return False
 
-        if _local.frame_locals is None:
-            while tb.tb_next is not None:
-                tb = tb.tb_next
-            _local.frame_locals = tb.tb_frame.f_locals
-
         if _local.level > 1:
             _local.level -= 1
             return False # the outermost caller should handle this
 
+        frames = []
+
+        while tb is not None:
+            if tb.tb_frame.f_locals.get("_ignore_locals_") or not tb.tb_frame.f_locals:
+                frames.append(None)
+            else:
+                frames.append(tb.tb_frame)
+            tb = tb.tb_next
+
         if _local.handler is None:
             _local.handler = chain_exceptions(exc_value)
 
-        variables = ["", None, "Local variables from innermost frame:", ""]
+        variables = ["", None, None]
 
         with _local.handler:
-            for name, value in _local.frame_locals.items():
-                variables.append("{0} = {1!r}".format(name, value))
+            for i, frame in enumerate(frames, start=1):
+                if frame is None:
+                    continue
+                variables.append("\nLocal variables from frame #{0} (in {1}):\n".format(i, frame.f_code.co_name))
+                for name, value in frame.f_locals.items():
+                    variables.append("{0} = {1!r}".format(name, value))
 
-        if len(variables) > 4:
+        if len(variables) > 3:
             variables.append("\n")
+            variables[2] = "Local variables in all frames (most recent call last):"
         else:
-            variables[2] = "No local variables found in innermost frame."
+            variables[2] = "No local variables found in all frames."
 
         variables[1] = _local.handler.traceback
 
@@ -176,6 +184,7 @@ class handle_error:
         return self
 
     def __call__(*args, **kwargs):
+        _ignore_locals_ = True
         self, *args = args
         if self.instance is not None:
             args = [self.instance] + args
@@ -226,6 +235,7 @@ class command:
 
     @handle_error
     def caller(self, cli, rawnick, chan, rest):
+        _ignore_locals_ = True
         user = users._add(cli, nick=rawnick) # FIXME
 
         if users.equals(chan, users.Bot.nick): # PM
@@ -339,6 +349,7 @@ class cmd:
 
     @handle_error
     def caller(self, cli, rawnick, chan, rest):
+        _ignore_locals_ = True
         if users.equals(chan, users.Bot.nick):
             chan = users.parse_rawnick_as_dict(rawnick)["nick"]