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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 D3A74C4CEC7 for ; Fri, 13 Sep 2019 14:50:16 +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 A81472089F for ; Fri, 13 Sep 2019 14:50:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A81472089F 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]:44806 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8mtr-00017s-DH for qemu-devel@archiver.kernel.org; Fri, 13 Sep 2019 10:50:15 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47999) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8mrJ-0007nD-GM for qemu-devel@nongnu.org; Fri, 13 Sep 2019 10:47:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i8mrI-0007G0-DO for qemu-devel@nongnu.org; Fri, 13 Sep 2019 10:47:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41136) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i8mrI-0007Fk-8S for qemu-devel@nongnu.org; Fri, 13 Sep 2019 10:47:36 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8914C10275E2; Fri, 13 Sep 2019 14:47:35 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-117-142.ams2.redhat.com [10.36.117.142]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 15B795B681; Fri, 13 Sep 2019 14:47:33 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 9B2A8113865F; Fri, 13 Sep 2019 16:47:31 +0200 (CEST) From: Markus Armbruster To: Eric Blake References: <20190910063724.28470-1-armbru@redhat.com> <20190910063724.28470-10-armbru@redhat.com> <24172d8b-7504-2641-d15b-277235430c6e@redhat.com> Date: Fri, 13 Sep 2019 16:47:31 +0200 In-Reply-To: <24172d8b-7504-2641-d15b-277235430c6e@redhat.com> (Eric Blake's message of "Tue, 10 Sep 2019 11:30:14 -0500") Message-ID: <87y2ys8d8c.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.64]); Fri, 13 Sep 2019 14:47:35 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 09/16] qapi: Permit alternates with just one branch 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: marcandre.lureau@redhat.com, qemu-devel@nongnu.org, mdroth@linux.vnet.ibm.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eric Blake writes: > On 9/10/19 1:37 AM, Markus Armbruster wrote: >> A union or alternate without branches makes no sense and doesn't work: >> it can't be instantiated. A union or alternate with just one branch >> works, but is degenerate. We accept the former, but reject the >> latter. Weird. docs/devel/qapi-code-gen.txt doesn't mention the >> difference. It claims an alternate definition is "is similar to a >> simple union type". >> >> Permit degenerate alternates to make them consistent with unions. >> >> Signed-off-by: Markus Armbruster >> --- >> scripts/qapi/common.py | 6 ++---- >> tests/qapi-schema/alternate-empty.err | 2 +- >> tests/qapi-schema/alternate-empty.json | 4 ++-- >> tests/qapi-schema/qapi-schema-test.json | 4 +++- >> tests/qapi-schema/qapi-schema-test.out | 6 ++++-- >> 5 files changed, 12 insertions(+), 10 deletions(-) > > Reviewed-by: Eric Blake > > (Might make sense if one of the branches is conditional, where depending > on compile-time options it could be a two-branch or a one-branch alternate) The QAPI generator doesn't even try to reason about conditions. It happily lets you define a union or alternate with branches that are all conditional, and where the conditions are all false for a particular build configuration. Ensuring the QAPI schema is sane for all build configurations is the schema author's problem.