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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 BE0D6C4361B for ; Thu, 17 Dec 2020 11:57:46 +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 17172238E9 for ; Thu, 17 Dec 2020 11:57:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 17172238E9 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]:39710 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kprui-0006sp-Ee for qemu-devel@archiver.kernel.org; Thu, 17 Dec 2020 06:57:44 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:51392) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kprtv-0006Sq-A7 for qemu-devel@nongnu.org; Thu, 17 Dec 2020 06:56:55 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:41440) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kprtt-00051A-3l for qemu-devel@nongnu.org; Thu, 17 Dec 2020 06:56:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608206212; 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=77vsFjyXEd1xt+mSuaouIZ9xJSMYgCUk+OzG8+d77fg=; b=fBUZ9FyYEX69DhtA/sNeSoUac8foLNxMPBOVb8mWgTQm5Z4OymS3l6ILAT9Kyg4EcT4LRH 0JNPDFu/wqDQfSDjAiIEOJto7VvDlzGw8UGsan9fjB+Z22v/601QJU3/LTfCbnOXJXa3qf 2HuLCBuFkQq8Xj1ELxtk87gIyDqknFo= 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-565-cOTNMW0vMpi0P6ch5mdVdw-1; Thu, 17 Dec 2020 06:56:50 -0500 X-MC-Unique: cOTNMW0vMpi0P6ch5mdVdw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7C28B59 for ; Thu, 17 Dec 2020 11:56:49 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-103.ams2.redhat.com [10.36.112.103]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1D18360CDE; Thu, 17 Dec 2020 11:56:46 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 8FD201130358; Thu, 17 Dec 2020 12:56:44 +0100 (CET) From: Markus Armbruster To: John Snow Subject: Re: [PATCH 06/12] qapi/source: Add builtin null-object sentinel References: <20201214235327.1007124-1-jsnow@redhat.com> <20201214235327.1007124-7-jsnow@redhat.com> <87r1nqrtp7.fsf@dusky.pond.sub.org> <9f25c91a-774d-fbe3-3780-5415e7a54524@redhat.com> Date: Thu, 17 Dec 2020 12:56:44 +0100 In-Reply-To: <9f25c91a-774d-fbe3-3780-5415e7a54524@redhat.com> (John Snow's message of "Wed, 16 Dec 2020 14:11:35 -0500") Message-ID: <87im90k5mr.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 2.79 on 10.5.11.13 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=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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 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: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Cleber Rosa , qemu-devel@nongnu.org, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" John Snow writes: > On 12/16/20 4:22 AM, Markus Armbruster wrote: >> 2. On error with "no source info", don't crash. >> I have my doubts on this one. >> Such an error means the QAPI code generator screwed up, at least >> in >> theory. Crashing is only proper. It gets the screwup fixed. >> > > QAPISemError and friends will also halt the generator and don't > produce output and will fail tests. They aren't less visible or more > ignorable somehow. > >> In practice, errors due to interactions between built-in stuff and >> user-defined stuff could conceivably escape testing. I can't >> remember such a case offhand. >> Will the "no source info" error be more useful than a crash? >> Possibly. Will it get the screwup fixed? Maybe not. > > I don't understand this; if it's an error -- there's no QAPI, there's > no QEMU. It's definitely getting fixed. > > If QAPISourceInfo is primarily used for printing error information, we > are already in a situation where the generator is hosed and has > wandered itself into a problem that can't be ignored. > > There's no additional value in having python crash twice per every > crash because we have bad types in our error reporting functions. Consider the following scenario. The average developer knows just enough about QAPI to be dangerous. That's okay; if you had to be a QAPI expert to modify the QAPI schema, we would have failed. Now meet Joe Average. He's a good guy. Today his job happens to require extending the QAPI schema. In a hurry, as usual. So Joe brings his well-honed voodoo programming skills to bear, and writes something that looks plausible to him. His build fails. He's not surprised; he's voodoo- programming after all. However, the error message is less clear than usual. Something about a '[builtin]' file. There is no '[builtin]' file. What to do? Obvious! If a bit of voodoo doesn't get you over the finish line, use more: twiddle the schema until it works. If his build failed with a Python backtrace instead, Joe would immediately know that he ran into a bug in our tooling he should report. Again, I don't mean to criticize Joe. I've walked in his shoes myself.