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bh=10jS/7Vy2njZo1HGDqR6VGuUPI4J0UkRssAK0rm8EGE=; b=Ux9kIbiLEF/AGBFzAfgyOQCV3EVACHoa4z5oqioAlYP9Q2ckXE6gvFcRrtwvX5ANiXii+M aY7GbXsIITrA1BtUt5RsLiY7Y00y3IMUULG36UiLmP0bEyXRrtOMPJ7g+eRsdSsBNlIWZM M/FKS6O0SlKlzy4j2+yyjNHYw14w+Cc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-130-2gKYEkNWPBqDODh_f92EDA-1; Thu, 24 Sep 2020 19:52:06 -0400 X-MC-Unique: 2gKYEkNWPBqDODh_f92EDA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 033F6344F3; Thu, 24 Sep 2020 23:52:05 +0000 (UTC) Received: from localhost.localdomain (ovpn-119-55.rdu2.redhat.com [10.10.119.55]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DF1BB73684; Thu, 24 Sep 2020 23:52:03 +0000 (UTC) Date: Thu, 24 Sep 2020 19:52:02 -0400 From: Cleber Rosa To: John Snow Subject: Re: [PATCH v2 36/38] qapi/visit.py: assert tag_member contains a QAPISchemaEnumType Message-ID: <20200924235202.GD347918@localhost.localdomain> References: <20200922210101.4081073-1-jsnow@redhat.com> <20200922210101.4081073-37-jsnow@redhat.com> <20200924191047.GH191229@localhost.localdomain> <3f37ab45-fd5b-ad8b-f033-d7887d1d6d93@redhat.com> MIME-Version: 1.0 In-Reply-To: <3f37ab45-fd5b-ad8b-f033-d7887d1d6d93@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=crosa@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="LKTjZJSUETSlgu2t" Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=crosa@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/24 01:10:00 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.199, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Eduardo Habkost , qemu-devel@nongnu.org, Michael Roth , Markus Armbruster , Alex =?iso-8859-1?Q?Benn=E9e?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --LKTjZJSUETSlgu2t Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Sep 24, 2020 at 03:36:23PM -0400, John Snow wrote: > On 9/24/20 3:10 PM, Cleber Rosa wrote: > > On Tue, Sep 22, 2020 at 05:00:59PM -0400, John Snow wrote: > > > Signed-off-by: John Snow > > > --- > > > scripts/qapi/visit.py | 15 ++++++++++----- > > > 1 file changed, 10 insertions(+), 5 deletions(-) > > >=20 > > > diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py > > > index 4edaee33e3..180c140180 100644 > > > --- a/scripts/qapi/visit.py > > > +++ b/scripts/qapi/visit.py > > > @@ -22,7 +22,10 @@ > > > indent, > > > ) > > > from .gen import QAPISchemaModularCVisitor, ifcontext > > > -from .schema import QAPISchemaObjectType > > > +from .schema import ( > > > + QAPISchemaEnumType, > > > + QAPISchemaObjectType, > > > +) > > > def gen_visit_decl(name, scalar=3DFalse): > > > @@ -84,15 +87,17 @@ def gen_visit_object_members(name, base, members,= variants): > > > ret +=3D gen_endif(memb.ifcond) > > > if variants: > > > + tag_member =3D variants.tag_member > > > + assert isinstance(tag_member.type, QAPISchemaEnumType) > > > + > >=20 > > I'd be interested in knowing why this wasn't left to be handled by the > > type checking only. Anyway, > >=20 >=20 > QAPISchemaVariants is a container type that is used to house a number of > QAPISchemaVariant types; but it (can) also take a tag_member to identify = one > of the fields in the variants that can be used to differentiate them. >=20 > Now, we assert that tag_member must be a QAPISchemaObjectTypeMember. > QAPISchemaVariant is also a QAPISchemaObjectTypeMember. >=20 > a QAPISchemaObjectTypeMember is a QAPISchemaMember. a QAPISchemaMember > describes one 'member' of either an enum, a features list, or an object > member. >=20 > Now, the QAPISchemaObjectTypeMember (and not the QAPISchemaMember!) serve= s > as a container for a QAPISchemaType -- this is a wrapper type, effectivel= y. > That contained type can be *anything*, because object members can be > *anything*. >=20 > Oops, but if we zoom back out, we are only able to constrain tag_member t= o > being a QAPISchemaObjectTypeMember, we have no expressive power over its > contained type. >=20 > That's why you need the assertion here; because of a loss of specificity > when we declare tag_member. >=20 >=20 > "Wow, John, it sounds like you should use a Generic type to be able to > describe the inner type of a QAPISchemaObjectTypeMember?" >=20 > Uh, yup, you're right! I should. But it's complicated, because > QAPISchemaMember does not have a contained type. Further, the contained t= ype > of a Member may or may not be known at construction time right now. >=20 > It's fixable, and probably involves adding something like a "string > constant" dummy type to allow QAPISchemaMember to have a contained type. >=20 > "Hey, all of that sounds very messy. What if we just added in a few > assertions for right now while we get the preliminary types in, and then = we > can make adjustments based on what makes the code prettier?" >=20 > Sounds like a plan, hypothetical quote person. >=20 > > Reviewed-by: Cleber Rosa > >=20 I did not attempt to learn the type names by heart (mental sanity first) but I get the big picture. 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