Re: [PATCH v6 19/19] qapi/introspect.py: add SchemaMetaType enum

[Markus Armbruster <armbru@redhat.com>]

John Snow <jsnow@redhat.com> writes:

> Follows the qapi/introspect.py definition of the same; this adds a more
> precise typing to _gen_tree's mtype parameter.
>
> NB: print(SchemaMetaType.BUILTIN) would produce the string
> "SchemaMetaType.BUILTIN", but when using format strings (.format or f-strings),
> it relies on the __format__ method defined in the Enum class, which uses the
> "value" of the enum instead, producing the string "builtin".
>
> For consistency with old-style format strings (which simply call the
> __str__ method of an object), a __str__ dunder is added, though it is
> not actually used here in this code.
>
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  scripts/qapi/introspect.py | 38 +++++++++++++++++++++++++++++---------
>  1 file changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
> index c6f5cf8d874..008a21f5c4c 100644
> --- a/scripts/qapi/introspect.py
> +++ b/scripts/qapi/introspect.py
> @@ -11,6 +11,7 @@
>  See the COPYING file in the top-level directory.
>  """
>  
> +from enum import Enum
>  from typing import (
>      Any,
>      Dict,
> @@ -79,6 +80,23 @@
>  SchemaInfoCommand = Dict[str, object]
>  
>  
> +class SchemaMetaType(str, Enum):
> +    """
> +    Mimics the SchemaMetaType enum from qapi/introspect.json.
> +    """
> +    BUILTIN = 'builtin'
> +    ENUM = 'enum'
> +    ARRAY = 'array'
> +    OBJECT = 'object'
> +    ALTERNATE = 'alternate'
> +    COMMAND = 'command'
> +    EVENT = 'event'
> +
> +    def __str__(self) -> str:
> +        # Needed for intuitive behavior with old-style format strings.
> +        return str(self.value)
> +
> +

The fanciness compared to plain Enum('SchemaMetaType', 'BUILTIN ...')
avoids extra code to map the enum values to the strings with need.

>  _ValueT = TypeVar('_ValueT', bound=_Value)
>  
>  
> @@ -251,7 +269,8 @@ def _gen_features(features: Sequence[QAPISchemaFeature]
>                        ) -> List[Annotated[str]]:
>          return [Annotated(f.name, f.ifcond) for f in features]
>  
> -    def _gen_tree(self, name: str, mtype: str, obj: Dict[str, object],
> +    def _gen_tree(self, name: str, mtype: SchemaMetaType,
> +                  obj: Dict[str, object],
>                    ifcond: Sequence[str] = (),
>                    features: Sequence[QAPISchemaFeature] = ()) -> None:
>          """
> @@ -299,7 +318,7 @@ def _gen_variant(self, variant: QAPISchemaVariant
>  
>      def visit_builtin_type(self, name: str, info: Optional[QAPISourceInfo],
>                             json_type: str) -> None:
> -        self._gen_tree(name, 'builtin', {'json-type': json_type})
> +        self._gen_tree(name, SchemaMetaType.BUILTIN, {'json-type': json_type})
>  
>      def visit_enum_type(self, name: str, info: Optional[QAPISourceInfo],
>                          ifcond: Sequence[str],
> @@ -307,7 +326,7 @@ def visit_enum_type(self, name: str, info: Optional[QAPISourceInfo],
>                          members: List[QAPISchemaEnumMember],
>                          prefix: Optional[str]) -> None:
>          self._gen_tree(
> -            name, 'enum',
> +            name, SchemaMetaType.ENUM,
>              {'values': [Annotated(m.name, m.ifcond) for m in members]},
>              ifcond, features
>          )
> @@ -316,8 +335,8 @@ def visit_array_type(self, name: str, info: Optional[QAPISourceInfo],
>                           ifcond: Sequence[str],
>                           element_type: QAPISchemaType) -> None:
>          element = self._use_type(element_type)
> -        self._gen_tree('[' + element + ']', 'array', {'element-type': element},
> -                       ifcond)
> +        self._gen_tree('[' + element + ']', SchemaMetaType.ARRAY,
> +                       {'element-type': element}, ifcond)
>  
>      def visit_object_type_flat(self, name: str, info: Optional[QAPISourceInfo],
>                                 ifcond: Sequence[str],
> @@ -330,14 +349,14 @@ def visit_object_type_flat(self, name: str, info: Optional[QAPISourceInfo],
>          if variants:
>              obj['tag'] = variants.tag_member.name
>              obj['variants'] = [self._gen_variant(v) for v in variants.variants]
> -        self._gen_tree(name, 'object', obj, ifcond, features)
> +        self._gen_tree(name, SchemaMetaType.OBJECT, obj, ifcond, features)
>  
>      def visit_alternate_type(self, name: str, info: Optional[QAPISourceInfo],
>                               ifcond: Sequence[str],
>                               features: List[QAPISchemaFeature],
>                               variants: QAPISchemaVariants) -> None:
>          self._gen_tree(
> -            name, 'alternate',
> +            name, SchemaMetaType.ALTERNATE,
>              {'members': [Annotated({'type': self._use_type(m.type)},
>                                     m.ifcond)
>                           for m in variants.variants]},
> @@ -361,7 +380,7 @@ def visit_command(self, name: str, info: Optional[QAPISourceInfo],
>          }
>          if allow_oob:
>              obj['allow-oob'] = allow_oob
> -        self._gen_tree(name, 'command', obj, ifcond, features)
> +        self._gen_tree(name, SchemaMetaType.COMMAND, obj, ifcond, features)
>  
>      def visit_event(self, name: str, info: Optional[QAPISourceInfo],
>                      ifcond: Sequence[str], features: List[QAPISchemaFeature],
> @@ -370,7 +389,8 @@ def visit_event(self, name: str, info: Optional[QAPISourceInfo],
>          assert self._schema is not None
>  
>          arg_type = arg_type or self._schema.the_empty_object_type
> -        self._gen_tree(name, 'event', {'arg-type': self._use_type(arg_type)},
> +        self._gen_tree(name, SchemaMetaType.EVENT,
> +                       {'arg-type': self._use_type(arg_type)},
>                         ifcond, features)

Gain: _gen_tree()'s second argument's type now serves as documentation,
and passing crap to it becomes harder.

Gut feeling: too much notational overhead for too little gain.

Opinions?