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Thu, 25 Feb 2021 13:07:20 +0100 (CET) From: Markus Armbruster To: John Snow Subject: Re: [PATCH v3 07/16] qapi/expr.py: Add casts in a few select cases References: <20210223003408.964543-1-jsnow@redhat.com> <20210223003408.964543-8-jsnow@redhat.com> <87zgzt1w9w.fsf@dusky.pond.sub.org> <9b9b1b1d-1988-2bbd-4f6e-6374ebd3cd88@redhat.com> Date: Thu, 25 Feb 2021 13:07:19 +0100 In-Reply-To: <9b9b1b1d-1988-2bbd-4f6e-6374ebd3cd88@redhat.com> (John Snow's message of "Wed, 24 Feb 2021 17:24:31 -0500") Message-ID: <87czwos64o.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=63.128.21.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=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: Michael Roth , qemu-devel@nongnu.org, Eduardo Habkost , Cleber Rosa Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" John Snow writes: > On 2/24/21 7:32 AM, Markus Armbruster wrote: >> John Snow writes: >> >>> Casts are instructions to the type checker only, they aren't "safe" and >>> should probably be avoided in general. In this case, when we perform >>> type checking on a nested structure, the type of each field does not >>> "stick". >>> >>> We don't need to assert that something is a str if we've already checked >>> that it is -- use a cast instead for these cases. >>> >>> Signed-off-by: John Snow >>> Reviewed-by: Eduardo Habkost >>> Reviewed-by: Cleber Rosa >>> --- >>> scripts/qapi/expr.py | 8 ++++---- >>> 1 file changed, 4 insertions(+), 4 deletions(-) >>> >>> diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py >>> index afa6bd07769..f45d6be1f4c 100644 >>> --- a/scripts/qapi/expr.py >>> +++ b/scripts/qapi/expr.py >>> @@ -15,7 +15,7 @@ >>> # See the COPYING file in the top-level directory. >>> >>> import re >>> -from typing import MutableMapping, Optional >>> +from typing import MutableMapping, Optional, cast >>> >>> from .common import c_name >>> from .error import QAPISemError >>> @@ -232,7 +232,7 @@ def check_enum(expr, info): >>> >>> >>> def check_struct(expr, info): >>> - name = expr['struct'] >>> + name = cast(str, expr['struct']) # Asserted in check_exprs >>> members = expr['data'] >>> >> >> I believe you need this only so you can declare check_type()'s >> allow_dict to be Optional[str]. More busy-work around allow_dict... >> >> I'm tempted to ask for allow_dict: Any and call it a day. >> > > You're right, this is because of the signature for the allow_dict > argument. Ultimately, the pragma is a collection of strings and we need > to prove we are looking up a string somewhere or other. > > (Or tell the type checker to leave us alone.) > > Unfortunately, the "check" in check_exprs falls off almost immediately. What do you mean by "falls off"? > Working with dictly-typed objects is a little annoying for this reason. > > This works for now; but finding a better way to do the pragma checks is > probably the more correct thing. (And not something I really want to try > and get through review until we're done typing, I think.) Yes, there's probably a neater way to do the name case checking (with pragma-directed exceptions), and yes, we should refrain from looking for it right now. >>> check_type(members, info, "'data'", allow_dict=name) >>> @@ -240,7 +240,7 @@ def check_struct(expr, info): >>> >>> >>> def check_union(expr, info): >>> - name = expr['union'] >>> + name = cast(str, expr['union']) # Asserted in check_exprs >>> base = expr.get('base') >>> discriminator = expr.get('discriminator') >>> members = expr['data'] >> >> Likwewise. >> >>> @@ -337,7 +337,7 @@ def check_exprs(exprs): >>> else: >>> raise QAPISemError(info, "expression is missing metatype") >>> >>> - name = expr[meta] >>> + name = cast(str, expr[meta]) # Asserted right below: >> >> "Checked", not "asserted". >> > > Oh, yes. > >>> check_name_is_str(name, info, "'%s'" % meta) >>> info.set_defn(meta, name) >>> check_defn_name_str(name, info, meta) >> >> >> Cast before check gives me a queasy feeling. It's lying to the type >> checker. >> >> Hamfisted way to avoid lying: >> >> check_name_is_str(expr[meta], ...) >> name = cast(str, expr[meta]) >> >> Something like >> >> name = check_name_is_str(name, ...) >> >> might be neater, but then we'd have to find a better function name. >> > > OK, I'll look into re-ordering this. Thanks! To avoid misunderstandings: ham-fisted would do for now.