Re: [PATCH v4 07/14] qapi/introspect.py: Introduce preliminary tree typing

[Markus Armbruster <armbru@redhat.com>]

John Snow <jsnow@redhat.com> writes:

> The types will be used in forthcoming patches to add typing. These types
> describe the layout and structure of the objects passed to
> _tree_to_qlit, but lack the power to describe annotations until the next
> commit.
>
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  scripts/qapi/introspect.py | 30 +++++++++++++++++++++++++++++-
>  1 file changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
> index 0aa3b77109f..b82efe16f6e 100644
> --- a/scripts/qapi/introspect.py
> +++ b/scripts/qapi/introspect.py
> @@ -10,7 +10,13 @@
>  See the COPYING file in the top-level directory.
>  """
>  
> -from typing import Optional
> +from typing import (
> +    Any,
> +    Dict,
> +    List,
> +    Optional,
> +    Union,
> +)
>  
>  from .common import (
>      c_name,
> @@ -26,6 +32,28 @@
>  )
>  
>  
> +# This module constructs a tree data structure that is used to
> +# generate the introspection information for QEMU. It behaves similarly
> +# to a JSON value.
> +#
> +# A complexity over JSON is that our values may or may not be annotated.
> +#
> +# Un-annotated values may be:
> +#     Scalar: str, bool, None.
> +#     Non-scalar: List, Dict
> +# _value = Union[str, bool, None, Dict[str, TreeValue], List[TreeValue]]
> +#
> +# With optional annotations, the type of all values is:
> +# TreeValue = Union[_value, Annotated[_value]]
> +#
> +# Sadly, mypy does not support recursive types, so we must approximate this.
> +_stub = Any
> +_scalar = Union[str, bool, None]
> +_nonscalar = Union[Dict[str, _stub], List[_stub]]
> +_value = Union[_scalar, _nonscalar]
> +# TreeValue = Union[_value, 'Annotated[_value]']

Why is TreeValue commented out?  Oh, because Annotated doesn't exist,
yet.

Possibly less confusing:

   # A complexity over JSON is that our values may or may not be annotated.
   #
   # Un-annotated values may be:
   #     Scalar: str, bool, None.
   #     Non-scalar: List, Dict
   # _value = Union[str, bool, None, Dict[str, TreeValue], List[TreeValue]]
   #
   # With optional annotations, the type of all values is:
   # TODO
   #
   # Sadly, mypy does not support recursive types, so we must approximate this.
   _stub = Any
   _scalar = Union[str, bool, None]
   _nonscalar = Union[Dict[str, _stub], List[_stub]]
   _value = Union[_scalar, _nonscalar]

or even just

   # A complexity over JSON is that our values may or may not be annotated.
   #
   # Un-annotated values may be:
   #     Scalar: str, bool, None.
   #     Non-scalar: List, Dict
   # _value = Union[str, bool, None, Dict[str, TreeValue], List[TreeValue]]
   #
   # Sadly, mypy does not support recursive types, so we must approximate this.
   _stub = Any
   _scalar = Union[str, bool, None]
   _nonscalar = Union[Dict[str, _stub], List[_stub]]
   _value = Union[_scalar, _nonscalar]

> +
> +
>  def _make_tree(obj, ifcond, comment=None):
>      extra = {
>          'if': ifcond,