[PATCH v10 08/14] iotests: touch up log function signature

[John Snow]

Representing nested, recursive data structures in mypy is notoriously
difficult; the best we can reliably do right now is denote the leaf
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 to a specific type
per-invocation, like a Generic.

log() behaves as log<Msg>() now, where the incoming type informs the
signature it expects for any filter arguments passed in. If Msg is a
str, then filter should take and return a str.

Signed-off-by: John Snow <address@hidden>
Reviewed-by: Max Reitz <address@hidden>
---
 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 010bca526c..e2d3e89574 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