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 X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 84250C433E0 for ; Thu, 14 Jan 2021 13:41:27 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 234CD23A5D for ; Thu, 14 Jan 2021 13:41:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 234CD23A5D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:46196 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l02sQ-0006VO-3w for qemu-devel@archiver.kernel.org; Thu, 14 Jan 2021 08:41:26 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:53022) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l02qn-0004p9-Ll for qemu-devel@nongnu.org; Thu, 14 Jan 2021 08:39:45 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:36696) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l02ql-0006RM-MQ for qemu-devel@nongnu.org; Thu, 14 Jan 2021 08:39:45 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610631582; 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=Vv2jJRbCTwP3iYj5z/79QkMb8nEYttnFPCpTONWPIGc=; b=JQj8vehmzCLTh/3zj3u2ktBbXFnOlGhG2BDg+yI5q/90DibGkA+lbwfvGx6Pc/WX7qTmUb yfqn412dhqmTuN3KABIDtiZyr+qWZp761BfleOo/ag1PZEBFpsNAQy+pKYcKn0K+LxihMR KsR5nIBv0QvTeIJqz4YGZUp/4oH0Ews= 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-420-_WRzgKolMcWdTropBBJdQw-1; Thu, 14 Jan 2021 08:39:38 -0500 X-MC-Unique: _WRzgKolMcWdTropBBJdQw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3B4FC190A7A7; Thu, 14 Jan 2021 13:39:37 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-172.ams2.redhat.com [10.36.112.172]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D480419C78; Thu, 14 Jan 2021 13:39:36 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 68DC511386A7; Thu, 14 Jan 2021 14:39:35 +0100 (CET) From: Markus Armbruster To: John Snow Subject: Re: [PATCH v2 06/12] qapi/source: Add builtin null-object sentinel References: <20201217015927.197287-1-jsnow@redhat.com> <20201217015927.197287-7-jsnow@redhat.com> <878s8wyhgc.fsf@dusky.pond.sub.org> Date: Thu, 14 Jan 2021 14:39:35 +0100 In-Reply-To: (John Snow's message of "Wed, 13 Jan 2021 17:30:49 -0500") Message-ID: <87eeinab8o.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: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.248, 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 , Eduardo Habkost , qemu-devel@nongnu.org, =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Cleber Rosa Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" John Snow writes: > On 1/13/21 10:39 AM, Markus Armbruster wrote: >> Spelling nitpick: s/builtin/built-in/ in the title. >> > > Sure. > >> John Snow writes: >> >>> We use None to represent an object that has no source information >>> because it's a builtin. This complicates interface typing, since many >>> interfaces expect that there is an info object available to print errors >>> with. >>> >>> Introduce a special QAPISourceInfo that represents these built-ins so >>> that if an error should so happen to occur relating to one of these >>> builtins that we will be able to print its information, and interface >>> typing becomes simpler: you will always have a source info object. >>> >>> This object will evaluate as False, so "if info" remains a valid >>> idiomatic construct. >>> >>> NB: It was intentional to not allow empty constructors or similar to >>> create "empty" source info objects; callers must explicitly invoke >>> 'builtin()' to pro-actively opt into using the sentinel. This should >>> prevent use-by-accident. >>> >>> Signed-off-by: John Snow >> >> As I pointed out in review of v1, this patch has two aspects mixed up: >> >> 1. Represent "no source info" as special QAPISourceInfo instead of >> None >> >> 2. On error with "no source info", don't crash. >> >> The first one is what de-complicates interface typing. It's clearly >> serving this patch series' stated purpose: "static typing conversion". >> >> The second one is not. It sidetracks us into a design discussion that >> isn't related to static typing. Maybe it's something we should discuss. >> Maybe the discussion will make us conclude we want to do this. But >> letting the static typing work get delayed by that discussion would be >> stupid, and I'll do what I can to prevent that. >> > > It's not unrelated. It's about finding the most tactical incision to > make the types as we actually use them correct from a static analysis > context. > > Maybe there's another tactical incision to make that's "smaller", for > some perception of "smaller", but it's not unrelated. We don't have to debate, let alone agree on relatedness. >> The stupidest possible solution that preserves the crash is adding an >> assertion right where it crashes before this patch: in >> QAPISourceInfo.__str__(). Yes, crashing in a __str__() method is not >> nice, but it's no worse than before. Making it better than before is a >> good idea, and you're quite welcome to try, but please not in this >> series. Add a TODO comment asking for "make it better", then sit on >> your hands. > > I'm recently back from a fairly long PTO, so forgive me if I am > forgetting something, but I am not really sure I fundamentally > understand the nature of this critique. > > Making functions not "crash" is a side-effect of making the types > correct. I don't see it as scope-creep, it's a solution to a problem > under active consideration. I disagree. The crash you "fix" is *intentional*. I was too lazy to write something like assert self.info and instead relied in self.info.whatever to crash. I don't care how it crashes, as long as it does crash. I *like* qapi-gen to crash on such internal errors. It's easy, and makes "this is a bug, go report it" perfectly clear. I'd also be fine with reporting "internal error, this is a bug, go report it". Not in this series, unless it's utterly trivial, which I doubt. I'm *not* fine with feeding made-up info objects to the user error reporting machinery without proof that it'll actually produce a useful error message. Definitely not trivial, thus not in this series. > In my reply to your earlier critique, I (think) I mentioned that I > didn't understand the difference between: > > 1. An exception handler itself crashes because it received a value of > unexpected type, or > > 2. The exception handler printed a message that indicates a problem with > a built-in source definition. > > In either case, QAPI didn't get built and it printed some kind of error > spaghetti to the screen. In both cases, something much more seriously > wrong has happened and the error message likely does not prepare the > human user to really genuinely understand what that seriously wrong > thing is. > > I think this is an on-mission patch that improves circumstances; with > regards to matters of taste I would see it as a lateral move at worst > (one weird error for another weird error). > > I'm left a little confused by the pushback, so I don't feel equipped to > try and write code that addresses it. > > Let's chat on IRC? Gladly. If we can make out work days intersect...