Re: [PATCH v2 5/7] qapi/parser: [RFC] add QAPIExpression

[Markus Armbruster <armbru@redhat.com>]

John Snow <jsnow@redhat.com> writes:

> The idea here is to combine 'TopLevelExpr' and 'ParsedExpression' into
> one type that accomplishes the purposes of both types;
>
> 1. TopLevelExpr is meant to represent a JSON Object, but only those that
> represent what qapi-schema calls a TOP-LEVEL-EXPR, i.e. definitions,
> pragmas, and includes.
>
> 2. ParsedExpression is meant to represent a container around the above
> type, alongside QAPI-specific metadata -- the QAPISourceInfo and QAPIDoc
> objects.
>
> We can actually just roll these up into one type: A python mapping that
> has the metadata embedded directly inside of it.
>
> NB: This necessitates a change of typing for check_if() and
> check_keys(), because mypy does not believe UserDict[str, object] ⊆
> Dict[str, object]. It will, however, accept Mapping or
> MutableMapping. In this case, the immutable form is preferred as an
> input parameter because we don't actually mutate the input.
>
> Without this change, we will observe:
> qapi/expr.py:631: error: Argument 1 to "check_keys" has incompatible
> type "QAPIExpression"; expected "Dict[str, object]"
>
> Signed-off-by: John Snow <jsnow@redhat.com>

[...]

> diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py
> index f897dffbfd4..88f6fdfa67b 100644
> --- a/scripts/qapi/parser.py
> +++ b/scripts/qapi/parser.py

[...]

> @@ -38,21 +38,32 @@
>      from .schema import QAPISchemaFeature, QAPISchemaMember
>  
>  
> -#: Represents a single Top Level QAPI schema expression.
> -TopLevelExpr = Dict[str, object]
> -
>  # Return value alias for get_expr().
>  _ExprValue = Union[List[object], Dict[str, object], str, bool]
>  
> -# FIXME: Consolidate and centralize definitions for TopLevelExpr,
> -# _ExprValue, _JSONValue, and _JSONObject; currently scattered across
> -# several modules.
>  
> +# FIXME: Consolidate and centralize definitions for _ExprValue,
> +# JSONValue, and _JSONObject; currently scattered across several
> +# modules.
>  
> -class ParsedExpression(NamedTuple):
> -    expr: TopLevelExpr
> -    info: QAPISourceInfo
> -    doc: Optional['QAPIDoc']
> +
> +# 3.6 workaround: can be removed when Python 3.7+ is our required version.
> +if TYPE_CHECKING:
> +    _UserDict = UserDict[str, object]
> +else:
> +    _UserDict = UserDict
> +
> +
> +class QAPIExpression(_UserDict):
> +    def __init__(
> +        self,
> +        initialdata: Mapping[str, object],
> +        info: QAPISourceInfo,
> +        doc: Optional['QAPIDoc'] = None,
> +    ):

Style nitpick:

           doc: Optional['QAPIDoc'] = None):

> +        super().__init__(initialdata)
> +        self.info = info
> +        self.doc: Optional['QAPIDoc'] = doc
>  
>  
>  class QAPIParseError(QAPISourceError):

[...]