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

[Markus Armbruster]

John Snow <jsnow@redhat.com> writes:

> 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].

Do you mean "but self.members is declared as
List[QAPISchemaObjectTypeMember]"?

> +        # Cast down to the subtype.
> +        members = cast(List[QAPISchemaObjectTypeMember], list(seen.values()))

Let's break the line after the comma.

>  
>          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):