[PATCH v4 16/23] qapi/schema: Don't initialize "members" with `None`

[John Snow <jsnow@redhat.com>]

Declare, but don't initialize the "members" field with type
List[QAPISchemaObjectTypeMember].

This simplifies the typing from what would otherwise be
Optional[List[T]] to merely List[T]. This removes the need to add
assertions to several callsites that this value is not None - which it
never will be after the delayed initialization in check() anyway.

The type declaration without initialization trick will cause accidental
uses of this field prior to full initialization to raise an
AttributeError.

(Note that it is valid to have an empty members list, see the internal
q_empty object as an example. For this reason, we cannot use the empty
list as a replacement test for full initialization and instead rely on
the _checked/_check_complete fields.)

Signed-off-by: John Snow <jsnow@redhat.com>
---
 scripts/qapi/schema.py | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index 50ebc4f12de..fb30314741a 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -20,7 +20,7 @@
 from collections import OrderedDict
 import os
 import re
-from typing import List, Optional
+from typing import List, Optional, cast
 
 from .common import (
     POINTER_SUFFIX,
@@ -449,7 +449,7 @@ def __init__(self, name, info, doc, ifcond, features,
         self.base = None
         self.local_members = local_members
         self.variants = variants
-        self.members = None
+        self.members: List[QAPISchemaObjectTypeMember]
         self._check_complete = False
 
     def check(self, schema):
@@ -482,7 +482,11 @@ def check(self, schema):
         for m in self.local_members:
             m.check(schema)
             m.check_clash(self.info, seen)
-        members = seen.values()
+
+        # check_clash works in terms of the supertype, but local_members
+        # is asserted to be List[QAPISchemaObjectTypeMember].
+        # Cast down to the subtype.
+        members = cast(List[QAPISchemaObjectTypeMember], list(seen.values()))
 
         if self.variants:
             self.variants.check(schema, seen)
@@ -515,11 +519,9 @@ def is_implicit(self):
         return self.name.startswith('q_')
 
     def is_empty(self):
-        assert self.members is not None
         return not self.members and not self.variants
 
     def has_conditional_members(self):
-        assert self.members is not None
         return any(m.ifcond.is_present() for m in self.members)
 
     def c_name(self):
-- 
2.44.0