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 lists1p.gnu.org (lists1p.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 9676EC53219 for ; Mon, 27 Jul 2026 08:48:17 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1woH0G-0003na-82; Mon, 27 Jul 2026 04:48:04 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1woH0E-0003n3-Lz for qemu-devel@nongnu.org; Mon, 27 Jul 2026 04:48:02 -0400 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 1woH0D-0006Gr-9c for qemu-devel@nongnu.org; Mon, 27 Jul 2026 04:48:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1785142079; 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=vrF4VRHtybrXoarfKc7lVgALmoH8Hdj/KPP9O0tx5KY=; b=VxQO3IMYEeXzfI1eSOhjLDJfmFTAAOeYY9kZfp+5eOB/6UkhxZkJYZdJIBuvuQ181d8DFE l7O/MKIsNU2gNVAXhAQJi5wt4C8NeTW7QxNmICs+GNIx11cR2n74GTjKKZeFLED7qflku9 WmHbmref9tOy0Qff34sragSX3xqErTM= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-416-xwQxAvbkMtqtoTvQTiez_w-1; Mon, 27 Jul 2026 04:47:58 -0400 X-MC-Unique: xwQxAvbkMtqtoTvQTiez_w-1 X-Mimecast-MFC-AGG-ID: xwQxAvbkMtqtoTvQTiez_w_1785142077 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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 mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 04C50180063D for ; Mon, 27 Jul 2026 08:47:57 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.4]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B6D9E19560AB for ; Mon, 27 Jul 2026 08:47:56 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 27BF321E6920; Mon, 27 Jul 2026 10:47:54 +0200 (CEST) From: Markus Armbruster To: Paolo Bonzini Cc: qemu-devel@nongnu.org Subject: Re: [PATCH 2/3] scripts/qapi: reject empty enums In-Reply-To: <20260724130044.1369843-3-pbonzini@redhat.com> (Paolo Bonzini's message of "Fri, 24 Jul 2026 15:00:42 +0200") References: <20260724130044.1369843-1-pbonzini@redhat.com> <20260724130044.1369843-3-pbonzini@redhat.com> Date: Mon, 27 Jul 2026 10:47:54 +0200 Message-ID: <87a4rc24zp.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 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: -36 X-Spam_score: -3.7 X-Spam_bar: --- X-Spam_report: (-3.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.58, 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_PASS=-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: 2.1.29 Precedence: list List-Id: qemu development 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 Paolo Bonzini writes: > Raise an error if an enum has no members. Such enums cannot be populated > with a valid value, and therefore they can only be used as optional > members. But QAPI leaves out optional members from the serialization > protocol, and therefore the existence of the enum is completely pointless. > > The same limitation is not extended to an enum whose members are all > compiled out; these can still be useful as optional members. However they > cannot implicitly block usage of parent structures because, by virtue > of having only conditional members, they are "enums with conditional > first item" and must therefore be optional. > > Signed-off-by: Paolo Bonzini This one definitely needs to update docs/devel/qapi-code-gen.rst, because that one has Nothing prevents an empty enumeration, although it is probably not useful.