John Snow <js...@redhat.com> writes: > On Thu, Nov 23, 2023 at 9:12 AM Markus Armbruster <arm...@redhat.com> wrote: >> >> John Snow <js...@redhat.com> writes: >> >> > Dict[str, object] is a stricter type, but with the way that code is >> > currently arranged, it is infeasible to enforce this strictness. >> > >> > In particular, although expr.py's entire raison d'être is normalization >> > and type-checking of QAPI Expressions, that type information is not >> > "remembered" in any meaningful way by mypy because each individual >> > expression is not downcast to a specific expression type that holds all >> > the details of each expression's unique form. >> > >> > As a result, all of the code in schema.py that deals with actually >> > creating type-safe specialized structures has no guarantee (myopically) >> > that the data it is being passed is correct. >> > >> > There are two ways to solve this: >> > >> > (1) Re-assert that the incoming data is in the shape we expect it to be, or >> > (2) Disable type checking for this data. >> > >> > (1) is appealing to my sense of strictness, but I gotta concede that it >> > is asinine to re-check the shape of a QAPIExpression in schema.py when >> > expr.py has just completed that work at length. The duplication of code >> > and the nightmare thought of needing to update both locations if and >> > when we change the shape of these structures makes me extremely >> > reluctant to go down this route. >> > >> > (2) allows us the chance to miss updating types in the case that types >> > are updated in expr.py, but it *is* an awful lot simpler and, >> > importantly, gets us closer to type checking schema.py *at >> > all*. Something is better than nothing, I'd argue. >> > >> > So, do the simpler dumber thing and worry about future strictness >> > improvements later. >> >> Yes. > > (You were right, again.)
Occasionally happens ;) >> While Dict[str, object] is stricter than Dict[str, Any], both are miles >> away from the actual, recursive type. >> >> > Signed-off-by: John Snow <js...@redhat.com> >> > --- >> > scripts/qapi/parser.py | 3 ++- >> > 1 file changed, 2 insertions(+), 1 deletion(-) >> > >> > diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py >> > index bf31018aef0..b7f08cf36f2 100644 >> > --- a/scripts/qapi/parser.py >> > +++ b/scripts/qapi/parser.py >> > @@ -19,6 +19,7 @@ >> > import re >> > from typing import ( >> > TYPE_CHECKING, >> > + Any, >> > Dict, >> > List, >> > Mapping, >> > @@ -43,7 +44,7 @@ >> > _ExprValue = Union[List[object], Dict[str, object], str, bool] >> > >> > >> > -class QAPIExpression(Dict[str, object]): >> > +class QAPIExpression(Dict[str, Any]): >> > # pylint: disable=too-few-public-methods >> > def __init__(self, >> > data: Mapping[str, object], >> >> There are several occurences of Dict[str, object] elsewhere. Would your >> argument for dumbing down QAPIExpression apply to (some of) them, too? > > When and if they piss me off, sure. I'm just wary of making the types > too permissive because it can obscure typing errors; by using Any, you > really disable any further checks and might lead to false confidence > in the static checker. I still have a weird grudge against Any and > would like to fully eliminate it from any statically checked Python > code, but it's just not always feasible and I have to admit that "good > enough" is good enough. Doesn't have me running to lessen the > strictness in areas that didn't cause me pain, though... > >> Skimming them, I found this in introspect.py: >> >> # These types are based on structures defined in QEMU's schema, so we >> # lack precise types for them here. Python 3.6 does not offer >> # TypedDict constructs, so they are broadly typed here as simple >> # Python Dicts. >> SchemaInfo = Dict[str, object] >> SchemaInfoEnumMember = Dict[str, object] >> SchemaInfoObject = Dict[str, object] >> SchemaInfoObjectVariant = Dict[str, object] >> SchemaInfoObjectMember = Dict[str, object] >> SchemaInfoCommand = Dict[str, object] >> >> Can we do better now we have 3.8? > > A little bit, but it involves reproducing these types -- which are > ultimately meant to represent QAPI types defined in introspect.json -- > with "redundant" type info. i.e. I have to reproduce the existing type > definitions in Python-ese, and then we have the maintenance burden of > making sure they match. > > Maybe too much work to come up with a crazy dynamic definition thing > where we take the QAPI definition and build Python types from them ... > without some pretty interesting work to avoid the Ouroboros that'd > result. introspection.py wants static types based on types defined > dynamically by the schema definition; but we are not guaranteed to > have a suitable schema with these types at all. I'm not sure how to > express this kind of dependency without some interesting re-work. This > is a rare circumstance of the QAPI generator relying on the contents > of the Schema to provide static type assistance. > > Now, I COULD do it statically, since I don't expect these types to > change much, but I'm wary of how quickly it might get out of hand > trying to achieve better type specificity. > > General impression: "Not worth the hassle for this series, but we can > discuss proposals for future improvements" Fair enough. Thanks!
