[qemu-xen staging] python/qmp.py: add casts to JSON deserialization

[patchbot@xxxxxxx]

commit 2e2d93051753067fc5b888fdc18831127a4a900e
Author:     John Snow <jsnow@xxxxxxxxxx>
AuthorDate: Fri Jul 10 01:22:09 2020 -0400
Commit:     Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
CommitDate: Tue Jul 14 22:22:22 2020 +0200

    python/qmp.py: add casts to JSON deserialization
    
    mypy and python type hints are not powerful enough to properly describe
    JSON messages in Python 3.6. The best we can do, generally, is describe
    them as Dict[str, Any].
    
    Add casts to coerce this type for static analysis; but do NOT enforce
    this type at runtime in any way.
    
    Note: Python 3.8 adds a TypedDict construct which allows for the
    description of more arbitrary Dictionary shapes. There is a third-party
    module, "Pydantic", which is compatible with 3.6 that can be used
    instead of the JSON library that parses JSON messages to fully-typed
    Python objects, and may be preferable in some cases.
    
    (That is well beyond the scope of this commit or series.)
    
    Signed-off-by: John Snow <jsnow@xxxxxxxxxx>
    Reviewed-by: Kevin Wolf <kwolf@xxxxxxxxxx>
    Message-Id: <20200710052220.3306-6-jsnow@xxxxxxxxxx>
    Signed-off-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
---
 python/qemu/qmp.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/python/qemu/qmp.py b/python/qemu/qmp.py
index ef3c919b76..1ae36050a4 100644
--- a/python/qemu/qmp.py
+++ b/python/qemu/qmp.py
@@ -13,6 +13,7 @@ import socket
 import logging
 from typing import (
     Any,
+    cast,
     Dict,
     Optional,
     TextIO,
@@ -130,7 +131,10 @@ class QEMUMonitorProtocol:
             data = self.__sockfile.readline()
             if not data:
                 return None
-            resp = json.loads(data)
+            # By definition, any JSON received from QMP is a QMPMessage,
+            # and we are asserting only at static analysis time that it
+            # has a particular shape.
+            resp: QMPMessage = json.loads(data)
             if 'event' in resp:
                 self.logger.debug("<<< %s", resp)
                 self.__events.append(resp)
@@ -262,7 +266,7 @@ class QEMUMonitorProtocol:
         ret = self.cmd(cmd, kwds)
         if 'error' in ret:
             raise QMPResponseError(ret)
-        return ret['return']
+        return cast(QMPReturnValue, ret['return'])
 
     def pull_event(self, wait=False):
         """
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#staging