[PATCH v3 13/16] qapi/expr.py: Modify check_keys to accept any Collection

[John Snow]

This is a minor adjustment that allows the 'required' and 'optional'
keys fields to take a default value of an empty, immutable sequence (the
empty tuple).

This reveals a quirk of this function, which is that "a + b" is
list-specific behavior. We can accept a wider variety of types if we
avoid that behavior. Using Collection allows us to accept things like
lists, tuples, sets, and so on.

(Iterable would also have worked, but Iterable also includes things like
generator expressions which are consumed upon iteration, which would
require a rewrite to make sure that each input was only traversed once.)

Signed-off-by: John Snow <jsnow@redhat.com>
---
 scripts/qapi/expr.py | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py
index 2b96bec722f..0b841f292d7 100644
--- a/scripts/qapi/expr.py
+++ b/scripts/qapi/expr.py
@@ -33,6 +33,7 @@
 
 import re
 from typing import (
+    Collection,
     Iterable,
     List,
     MutableMapping,
@@ -133,8 +134,8 @@ def check_defn_name_str(name: str, info: QAPISourceInfo, 
meta: str) -> None:
 def check_keys(value: _JSObject,
                info: QAPISourceInfo,
                source: str,
-               required: List[str],
-               optional: List[str]) -> None:
+               required: Collection[str] = (),
+               optional: Collection[str] = ()) -> None:
     """
     Ensures an object has a specific set of keys. [Const]
 
@@ -155,7 +156,7 @@ def pprint(elems: Iterable[str]) -> str:
             "%s misses key%s %s"
             % (source, 's' if len(missing) > 1 else '',
                pprint(missing)))
-    allowed = set(required + optional)
+    allowed = set(required) | set(optional)
     unknown = set(value) - allowed
     if unknown:
         raise QAPISemError(
-- 
2.29.2