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Wed, 10 Jan 2024 07:58:08 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.71]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 490751121306; Wed, 10 Jan 2024 07:58:08 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 6142A21E6740; Wed, 10 Jan 2024 08:58:07 +0100 (CET) From: Markus Armbruster To: John Snow Cc: Markus Armbruster , qemu-devel@nongnu.org, Peter Maydell , Michael Roth Subject: Re: [PATCH 15/19] qapi/parser: demote QAPIExpression to Dict[str, Any] In-Reply-To: (John Snow's message of "Tue, 9 Jan 2024 19:14:39 -0500") References: <20231116014350.653792-1-jsnow@redhat.com> <20231116014350.653792-16-jsnow@redhat.com> <8734ww4kz4.fsf@pond.sub.org> Date: Wed, 10 Jan 2024 08:58:07 +0100 Message-ID: <877ckhfwmo.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -45 X-Spam_score: -4.6 X-Spam_bar: ---- X-Spam_report: (-4.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.493, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org John Snow writes: > On Thu, Nov 23, 2023 at 9:12=E2=80=AFAM Markus Armbruster wrote: >> >> John Snow 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'=C3=AAtre is normali= zation >> > 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 b= e, 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 >> > --- >> > 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 =3D Union[List[object], Dict[str, object], str, bool] >> > >> > >> > -class QAPIExpression(Dict[str, object]): >> > +class QAPIExpression(Dict[str, Any]): >> > # pylint: disable=3Dtoo-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 =3D Dict[str, object] >> SchemaInfoEnumMember =3D Dict[str, object] >> SchemaInfoObject =3D Dict[str, object] >> SchemaInfoObjectVariant =3D Dict[str, object] >> SchemaInfoObjectMember =3D Dict[str, object] >> SchemaInfoCommand =3D 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!