[PATCH v9 08/14] iotests: touch up log function signature

[John Snow <jsnow@redhat.com>]

Representing nested, recursive data structures in mypy is notoriously
difficult; the best we can reliably do right now is denote the atom
types as "Any" while describing the general shape of the data.

Regardless, this fully annotates the log() function.

Typing notes:

TypeVar is a Type variable that can optionally be constrained by a
sequence of possible types. This variable is bound per-invocation such
that the signature for filter=() requires that its callables take e.g. a
str and return a str.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 tests/qemu-iotests/iotests.py | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index c93c6b4557..3a049ece5b 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -28,6 +28,7 @@
 import struct
 import subprocess
 import sys
+from typing import (Any, Callable, Dict, Iterable, List, Optional, TypeVar)
 import unittest
 
 # pylint: disable=import-error, wrong-import-position
@@ -353,9 +354,16 @@ def _filter(_key, value):
         return value
     return filter_qmp(qmsg, _filter)
 
-def log(msg, filters=(), indent=None):
-    '''Logs either a string message or a JSON serializable message (like QMP).
-    If indent is provided, JSON serializable messages are pretty-printed.'''
+
+Msg = TypeVar('Msg', Dict[str, Any], List[Any], str)
+
+def log(msg: Msg,
+        filters: Iterable[Callable[[Msg], Msg]] = (),
+        indent: Optional[int] = None) -> None:
+    """
+    Logs either a string message or a JSON serializable message (like QMP).
+    If indent is provided, JSON serializable messages are pretty-printed.
+    """
     for flt in filters:
         msg = flt(msg)
     if isinstance(msg, (dict, list)):
-- 
2.21.1