Re: [PATCH 06/19] qapi/schema: adjust type narrowing for mypy's benefit

[Markus Armbruster]

John Snow <jsnow@redhat.com> writes:

> We already take care to perform some type narrowing for arg_type and
> ret_type, but not in a way where mypy can utilize the result. A simple
> change to use a temporary variable helps the medicine go down.
>
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  scripts/qapi/schema.py | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> index 4600a566005..a1094283828 100644
> --- a/scripts/qapi/schema.py
> +++ b/scripts/qapi/schema.py
> @@ -825,13 +825,14 @@ def __init__(self, name, info, doc, ifcond, features,
>      def check(self, schema):
>          super().check(schema)
>          if self._arg_type_name:
> -            self.arg_type = schema.resolve_type(
> +            arg_type = schema.resolve_type(
>                  self._arg_type_name, self.info, "command's 'data'")
> -            if not isinstance(self.arg_type, QAPISchemaObjectType):
> +            if not isinstance(arg_type, QAPISchemaObjectType):
>                  raise QAPISemError(
>                      self.info,
>                      "command's 'data' cannot take %s"
> -                    % self.arg_type.describe())
> +                    % arg_type.describe())
> +            self.arg_type = arg_type
>              if self.arg_type.variants and not self.boxed:
>                  raise QAPISemError(
>                      self.info,
> @@ -848,8 +849,7 @@ def check(self, schema):
>              if self.name not in self.info.pragma.command_returns_exceptions:
>                  typ = self.ret_type
>                  if isinstance(typ, QAPISchemaArrayType):
> -                    typ = self.ret_type.element_type
> -                    assert typ
> +                    typ = typ.element_type
>                  if not isinstance(typ, QAPISchemaObjectType):
>                      raise QAPISemError(
>                          self.info,
> @@ -885,13 +885,14 @@ def __init__(self, name, info, doc, ifcond, features, 
> arg_type, boxed):
>      def check(self, schema):
>          super().check(schema)
>          if self._arg_type_name:
> -            self.arg_type = schema.resolve_type(
> +            typ = schema.resolve_type(
>                  self._arg_type_name, self.info, "event's 'data'")
> -            if not isinstance(self.arg_type, QAPISchemaObjectType):
> +            if not isinstance(typ, QAPISchemaObjectType):
>                  raise QAPISemError(
>                      self.info,
>                      "event's 'data' cannot take %s"
> -                    % self.arg_type.describe())
> +                    % typ.describe())
> +            self.arg_type = typ
>              if self.arg_type.variants and not self.boxed:
>                  raise QAPISemError(
>                      self.info,

Harmless enough.  I can't quite see the mypy problem, though.  Care to
elaborate a bit?