From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CEFC1C61D9C for ; Wed, 22 Nov 2023 12:01:36 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1r5luV-0001mt-2f; Wed, 22 Nov 2023 07:00:52 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r5luT-0001mg-HZ for qemu-devel@nongnu.org; Wed, 22 Nov 2023 07:00:49 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r5luR-0002zn-NG for qemu-devel@nongnu.org; Wed, 22 Nov 2023 07:00:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1700654446; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=z5P/colIC8kFhRSaX0gV5bPJ2zQ9fyXpztbdLpGE1E0=; b=hUByC7YeV3+bzSOVzgVq6V+uaJ/eIMwGxkzaA564eBo48U+aRoZx0ZTo6QyMZfEW+4DRFv 5+4WF0DNVEvqQJmY6LylLUjpvGwHRJXkiDsSahunYktp8LyhOsJG9FJz3Bq8Ka60zQeKGQ sWzj+M9MHJBVwa2MlG1VOmQChxRcbhg= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-26-XZUoWA3gOXeA1LCpmOygmQ-1; Wed, 22 Nov 2023 07:00:42 -0500 X-MC-Unique: XZUoWA3gOXeA1LCpmOygmQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 770BF381A889; Wed, 22 Nov 2023 12:00:42 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.148]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3602A2026D4C; Wed, 22 Nov 2023 12:00:42 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 2FC5221E6A1F; Wed, 22 Nov 2023 13:00:41 +0100 (CET) From: Markus Armbruster To: John Snow Cc: qemu-devel , Peter Maydell , Michael Roth Subject: Re: [PATCH 06/19] qapi/schema: adjust type narrowing for mypy's benefit References: <20231116014350.653792-1-jsnow@redhat.com> <20231116014350.653792-7-jsnow@redhat.com> <87ttpf2o6t.fsf@pond.sub.org> Date: Wed, 22 Nov 2023 13:00:41 +0100 In-Reply-To: (John Snow's message of "Tue, 21 Nov 2023 11:36:19 -0500") Message-ID: <87cyw2uhee.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 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: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.058, 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 Tue, Nov 21, 2023, 9:09 AM Markus Armbruster wrote: > >> John Snow writes: >> >> > We already take care to perform some type narrowing for arg_type and >> > ret_type, but not in a way where mypy can utilize the result. A simple >> > change to use a temporary variable helps the medicine go down. >> > >> > Signed-off-by: John Snow >> > --- >> > scripts/qapi/schema.py | 17 +++++++++-------- >> > 1 file changed, 9 insertions(+), 8 deletions(-) >> > >> > diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py >> > index 4600a566005..a1094283828 100644 >> > --- a/scripts/qapi/schema.py >> > +++ b/scripts/qapi/schema.py >> > @@ -825,13 +825,14 @@ def __init__(self, name, info, doc, ifcond, features, >> > def check(self, schema): >> > super().check(schema) >> > if self._arg_type_name: >> > - self.arg_type = schema.resolve_type( >> > + arg_type = schema.resolve_type( >> > self._arg_type_name, self.info, "command's 'data'") >> > - if not isinstance(self.arg_type, QAPISchemaObjectType): >> > + if not isinstance(arg_type, QAPISchemaObjectType): >> > raise QAPISemError( >> > self.info, >> > "command's 'data' cannot take %s" >> > - % self.arg_type.describe()) >> > + % arg_type.describe()) >> > + self.arg_type = arg_type >> > if self.arg_type.variants and not self.boxed: >> > raise QAPISemError( >> > self.info, Same story as for QAPISchemaEvent.check() below. Correct? >> > @@ -848,8 +849,7 @@ def check(self, schema): >> > if self.name not in self.info.pragma.command_returns_exceptions: >> > typ = self.ret_type >> > if isinstance(typ, QAPISchemaArrayType): >> > - typ = self.ret_type.element_type >> > - assert typ >> > + typ = typ.element_type >> > > In this case, we've narrowed typ but not self.ret_type and mypy is not sure > they're synonymous here (lack of power in mypy's model, maybe?). Work in > terms of the temporary type we've already narrowed so mypy knows we have an > element_type field. The conditional ensures @typ is QAPISchemaArrayType. In mypy's view, @typ is QAPISchemaArrayType, but self.ret_type is only Optional[QAPISchemaType]. Therefore, it chokes on self.ret_type.element_type, but is happy with typ.element_type. Correct? Why delete the assertion? Oh! Hmm, should the deletion go into PATCH 10? >> if not isinstance(typ, QAPISchemaObjectType): >> > raise QAPISemError( >> > self.info, >> > @@ -885,13 +885,14 @@ def __init__(self, name, info, doc, ifcond, features, arg_type, boxed): >> > def check(self, schema): >> > super().check(schema) >> > if self._arg_type_name: >> > - self.arg_type = schema.resolve_type( >> > + typ = schema.resolve_type( >> > self._arg_type_name, self.info, "event's 'data'") >> > - if not isinstance(self.arg_type, QAPISchemaObjectType): >> > + if not isinstance(typ, QAPISchemaObjectType): >> > raise QAPISemError( >> > self.info, >> > "event's 'data' cannot take %s" >> > - % self.arg_type.describe()) >> > + % typ.describe()) >> > + self.arg_type = typ >> > if self.arg_type.variants and not self.boxed: >> > raise QAPISemError( >> > self.info, >> >> Harmless enough. I can't quite see the mypy problem, though. Care to >> elaborate a bit? >> > > self.arg_type has a narrower type- or, it WILL at the end of this series - > so we need to narrow a temporary variable first before assigning it to the > object state. > > We already perform the necessary check/narrowing, so this is really just > pointing out that it's a bad idea to assign the state before the type > check. Now we type check before assigning state. After PATCH 16, .resolve_type() will return QAPISchemaType, and self.arg_type will be Optional[QAPISchemaObjectType]. Correct?