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 1CC9BC47077 for ; Tue, 16 Jan 2024 15:56:43 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rPlnA-0004vp-M3; Tue, 16 Jan 2024 10:55:56 -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 1rPln8-0004vL-FC for qemu-devel@nongnu.org; Tue, 16 Jan 2024 10:55:54 -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 1rPln6-0005IH-OF for qemu-devel@nongnu.org; Tue, 16 Jan 2024 10:55:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1705420552; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dfBTUTjv64atHp3NMnHF3PNL8Y6QTayxRi8yILG5HKo=; b=dpHtVyl3jKry7ndsIX37wzARk/S22LMrn4bm9P+sjSTDWs18z8c32SdmWdag32rk96WqCO lWHEsw0EZmjr2RQQYEwkZRDFNzPYtdrwth76J+4pHg7xlE+QacuV85OqhgU6Fdo49LEBAR IMGQsV6c3COp5QBsnjL1jopXOZPftrA= Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-120-Zwzp5PPMMMmzo-XHM_4fXQ-1; Tue, 16 Jan 2024 10:55:50 -0500 X-MC-Unique: Zwzp5PPMMMmzo-XHM_4fXQ-1 Received: by mail-pg1-f199.google.com with SMTP id 41be03b00d2f7-5ce53c43ea1so5922804a12.2 for ; Tue, 16 Jan 2024 07:55:50 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1705420549; x=1706025349; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=dfBTUTjv64atHp3NMnHF3PNL8Y6QTayxRi8yILG5HKo=; b=IsbHVmYvprcIwHBvAbP9dEmvXKp8lKU+gxmrYCBntLvVrnOIxm6lp2lgB4qvjJri87 +AZENeddO0sC7ttzmLdrxVc7ahOXflWaAJWWwumPP4DBQwMzwzm1vVApggOlIhrIquGC uG4ZSWa9m31J7DwDgGgHhcdkbAtGXmHDJQ9Urn7czZ4zK9H//RVBrUrOuttwjRVHthla +hhrBLdTP1rTqKDuzy7hmqSOOnEt5/DqM2l/8eeWjdW2F3Po54jl0G5KpKs+zugA5v+3 sUXrKLJHUBuGsNKX4/T6HNFw2ClRo6qAvGOoQrPIPM9nlyi3HRAMBh/tyCkP9x7LC0H+ xkdA== X-Gm-Message-State: AOJu0YyC9RsWarzRZH9M5E5PPGboyZNPqfCfSdxePc2X7Rj7Q8UxRCUu NPjgQMTpmBguEuwgTYWU86lwAlWZZnD8M6iSDjIjNWYsPXFAFrRfDJ0678TcZe6Xgb/vBCM8xCH SxQOOQhJyEFu03tbM6S24U2rXt+XgLxLUlQFBURQ= X-Received: by 2002:a17:90a:c582:b0:28e:7a18:aa5d with SMTP id l2-20020a17090ac58200b0028e7a18aa5dmr799817pjt.39.1705420549570; Tue, 16 Jan 2024 07:55:49 -0800 (PST) X-Google-Smtp-Source: AGHT+IH7mh+XIbvcFhhmDeDgqGp2dmV92leysBddJ7IUYz/4uLHBisaP5kDvnImK0RtuAC5MgeFrr+VPIVQmmVGjZAs= X-Received: by 2002:a17:90a:c582:b0:28e:7a18:aa5d with SMTP id l2-20020a17090ac58200b0028e7a18aa5dmr799810pjt.39.1705420549291; Tue, 16 Jan 2024 07:55:49 -0800 (PST) MIME-Version: 1.0 References: <20240112222945.3033854-1-jsnow@redhat.com> <20240112222945.3033854-5-jsnow@redhat.com> <8734uyd7ol.fsf@pond.sub.org> In-Reply-To: <8734uyd7ol.fsf@pond.sub.org> From: John Snow Date: Tue, 16 Jan 2024 10:55:38 -0500 Message-ID: Subject: Re: [PATCH v2 04/19] qapi/schema: declare type for QAPISchemaObjectTypeMember.type To: Markus Armbruster Cc: qemu-devel@nongnu.org, Michael Roth , Peter Maydell Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.133.124; envelope-from=jsnow@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -38 X-Spam_score: -3.9 X-Spam_bar: --- X-Spam_report: (-3.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.806, 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 On Mon, Jan 15, 2024 at 8:53=E2=80=AFAM Markus Armbruster wrote: > > John Snow writes: > > > declare, but don't initialize the type of "type" to be QAPISchemaType - > > Declare > > > and allow the value to be initialized during check(). This creates a > > form of delayed initialization for QAPISchemaType objects where the > > static typing only represents the fully-realized object, which occurs > > after check() has been called. > > > > This avoids the need for several "assert type is not None" statements > > littered throughout the code by asserting it "will always be set." > > Uh, I find "will always be set" confusing. > > I think you mean "cannot be None". Yuh > > But "be set" can also be read as "will have a value". ...yuh > > It actually doesn't exist until .check(), and once it exists, it cannot > be None. > > > Note that the static typing information for this object will be > > incorrect prior to check() being called. If this field is accessed > > before it is initialized in check(), you'll be treated to an > > AttributeError exception. > > We could now enter a philosophical debate on whether the static typing > is actually incorrect. Clearly v: T asserts that the value of @v is > always a T, and the type checker proves this. Does it also assert that > @v exists? The type checker doesn't care, and that's a feature. *clutches TAPL and cries* > > Maybe start with the problem, and then develop the solution: > > A QAPISchemaObjectTypeMember's type gets resolved only during .check(). > We have QAPISchemaObjectTypeMember.__init__() initialize self.type =3D > None, and .check() assign the actual type. Using .type before .check() > is wrong, and hopefully crashes due to the value being None. Works. > > However, it makes for awkward typing. With .type: > Optional[QAPISchemaType], mypy is of course unable to see that it's Non= e > before .check(), and a QAPISchemaType after. To help it over the hump, > we'd have to assert self.type is not None before all the (valid) uses. > The assertion catches invalid uses, but only at run time; mypy can't > flag them. > > Instead, declare .type in .__init__() as QAPISchemaType *without* > initializing it. Using .type before .check() now certainly crashes, > which is an improvement. Mypy still can't flag invalid uses, but that'= s > okay. > OK. --js > > Fixes stuff like this: > > > > qapi/schema.py:657: error: "None" has no attribute "alternate_qtype" [= attr-defined] > > qapi/schema.py:662: error: "None" has no attribute "describe" [attr-de= fined] > > > > Signed-off-by: John Snow > > --- > > scripts/qapi/schema.py | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py > > index e39ed972a80..48a51dcd188 100644 > > --- a/scripts/qapi/schema.py > > +++ b/scripts/qapi/schema.py > > @@ -794,7 +794,7 @@ def __init__(self, name, info, typ, optional, ifcon= d=3DNone, features=3DNone): > > assert isinstance(f, QAPISchemaFeature) > > f.set_defined_in(name) > > self._type_name =3D typ > > - self.type =3D None > > + self.type: QAPISchemaType # set during check() > > self.optional =3D optional > > self.features =3D features or [] >