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=-7.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 12A37C433DF for ; Mon, 3 Aug 2020 17:26:26 +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 D57122086A for ; Mon, 3 Aug 2020 17:26:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="L+cjliQ3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D57122086A 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]:42456 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k2eED-0001r0-Vw for qemu-devel@archiver.kernel.org; Mon, 03 Aug 2020 13:26:26 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60566) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k2eDW-0001NS-OU for qemu-devel@nongnu.org; Mon, 03 Aug 2020 13:25:42 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:58900 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1k2eDU-00049A-J8 for qemu-devel@nongnu.org; Mon, 03 Aug 2020 13:25:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596475539; 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=UiPcMaM086DcWe/1lFtVqhl4s0VMj9rjjXaA5Ip7NJU=; b=L+cjliQ3NqGUpZVt3LBBYuTn6d8I3lSOYjQ2TMfG0XhVEr4se/cA1dxMSwIq+ptQc9iMsa q3tCYpjcbanabKhwlZQzl/ycBOjqT6mb9EZi04kxNEjFx78juIXFiPcrN4Xv8bHjBPm9XA PS/GifnGB+0T2mCatdEw2SF6JviLAP4= 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-493-IvzovwRjPNeJK59UT7ALuw-1; Mon, 03 Aug 2020 13:25:35 -0400 X-MC-Unique: IvzovwRjPNeJK59UT7ALuw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4A5FB800138 for ; Mon, 3 Aug 2020 17:25:34 +0000 (UTC) Received: from [10.3.113.122] (ovpn-113-122.phx2.redhat.com [10.3.113.122]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0506B60BF4; Mon, 3 Aug 2020 17:25:33 +0000 (UTC) Subject: Re: qapi-schema esotera To: John Snow , Markus Armbruster References: <5bfa3895-304d-8372-c0db-fda4c1a1ba59@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Mon, 3 Aug 2020 12:25:33 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <5bfa3895-304d-8372-c0db-fda4c1a1ba59@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/03 02:37:52 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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: QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/3/20 11:49 AM, John Snow wrote: > UNION is split into two primary forms: > > 1. Simple (No discriminator nor base) > 2. Flat (Discriminator and base) > > In expr.py, I notice that we modify the perceived type of the 'type' > expression based on the two union forms. > > 1a. Simple unions allow Array[T] > 1b. Flat unions disallow Array[T] Rather, branches in a simple unions are syntactic sugar for a wrapper struct that contains a single member 'data'; because of that extra nesting, the type of that single member is unconstrained. In flat unionw, the type MUST be a QAPI struct, because its members will be used inline; as currently coded, this prevents the use of an intrinsic type ('int', 'str') or an array type. If you need to use an array type in a flat union, you can't do: { 'union' ... 'data': { 'foo': [ 'MyBranch' ] } } but you can provide a wrapper type yourself: { 'struct': 'MyBranch', 'data': { 'array': [ 'MyType' ] } } { 'union' ... 'data': { 'foo': 'MyBranch' } } > > From the docs: > > Syntax: >     UNION = { 'union': STRING, >               'data': BRANCHES, >               '*if': COND, >               '*features': FEATURES } >           | { 'union': STRING, >               'data': BRANCHES, >               'base': ( MEMBERS | STRING ), >               'discriminator': STRING, >               '*if': COND, >               '*features': FEATURES } >     BRANCHES = { BRANCH, ... } >     BRANCH = STRING : TYPE-REF >            | STRING : { 'type': TYPE-REF, '*if': COND } > > Both arms use the same "BRANCHES" grammar production, which both use > TYPE-REF. > >     TYPE-REF = STRING | ARRAY-TYPE >     ARRAY-TYPE = [ STRING ] > > Implying that List[T] should be allowed for both productions. > Can I ask for a ruling from the judges? As you found, the docs are a bit misleading; the semantic constraint on flat union branches being a struct (because they will be inlined) prevents the use of type-refs that are valid in simple unions (where those simple types will be wrapped in an implicit struct). A patch to improve the docs would be a reasonable idea. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org